Insights into dietary supplements as popular product supporting the diet

Abstract

Changing lifestyles and the rising incidence of lifestyle diseases are causing people to increasingly turn to dietary supplements, often perceived as therapeutic measures aimed at maintaining or improving health. Although supplements cannot be marketed for the treatment or prevention of disease, many people assume they will improve health, alleviate the course of illness, or, for example, delay the aging process. Unfortunately, this is not true. Furthermore, people around the world often choose to treat illnesses with supplements instead of consulting with specialists and undergoing appropriate treatment. Information on supplement safety and some common interactions with drugs and food was gathered based on an analysis of numerous websites, databases, and publications. This analysis presents statistical data, current legal regulations, the advantages and disadvantages of supplementation, and highlights the importance of supplement control. It turns out that manufacturers are generally exempt from conducting costly and lengthy clinical trials by classifying their products as dietary supplements. This misinformation prevents consumers from making informed decisions about their use. Educating the public about the safety, benefits, and risks of dietary supplements is crucial. These topics should serve as a starting point for a broader discussion about the need for quality control and access to safe dietary supplements. Raising public awareness of healthcare in its broadest sense is crucial.

Introduction

The changing lifestyle of society and the increase in the occurrence of civilization diseases (e.g., obesity, depression, neurodegeneration) mean that people are increasingly reaching concentrated sources of minerals, vitamins, and other nutrients. They are handled as a remedy to maintain or strengthen health, which is not always the case (Shahidi 2012; https://food.ec.europa.eu/food-safety/labelling-and-nutrition/food-supplements_en).

Dietary supplements are most commonly defined as foodstuffs intended to supplement the diet in nutrients, which might be missing from a diet, that contain one or more of the following dietary ingredients: vitamin, mineral, herb or other botanical, amino acid; a dietary substance to supplement the diet by increasing the total daily intake, or a concentrate, metabolite, constituent, extract, or combination of these ingredients (www.fda.gov; https://food.ec.europa.eu). They come in a variety of forms (including tablets, powders, capsules, drinks, bars) and can be found in pharmacies, supermarkets, health food shops, and, especially in recent years, on the internet. Dietary supplements may be used to meet dietary needs or supplement nutritional deficiencies, but they are not intended to substitute for a healthy diet (Bellows and Moore 2013).

It is important to remember that they are regulated as a food class and not as drugs (https://crsreports.congress.gov/product/pdf/R/R43062/6). The main difference between supplements and medicines is that supplements are single substances or mixtures found mainly in low concentrations and intended to supplement the diet, whereas pharmaceutical products are targeted compounds that are used to treat diseases and alleviate ailments. Some dietary supplements are formulated under special conditions in controlled laboratories and carefully labeled. In the case of others, shortcomings are found, and sometimes they do not contain any of the substances indicated on the labels. Moreover, some supplements contain other substances that are not labeled on packaging – such as herbs, fillers, or substances known to cause damage. Furthermore, supplements do not undergo any evaluation process or testing before they are sold to customers, unlike pharmaceuticals that are tested during clinical trials (Denham 2011; Harris et al. 2004; Harvie 2014; https://eur-lex.europa.eu). Decision-making authorities in various countries (including the USA and the European Union (EU)) put supplements in a special category. A major change in the control and regulation of supplements took place when the US Congress passed the Dietary Supplement Health and Education Act (DSHEA) of 1994, which modified the 1958 Food Additive Amendments to the Federal Food, Drug, and Cosmetic Act. DSHEA defines a dietary supplement as “a product, other than tobacco, intended to supplement the diet”, a drug is an article used to “diagnose, cure, mitigate, treat, or prevent diseases”. In other words, a dietary supplement aims to complement the diet by increasing the dietary consumption of a certain substance (Camire and Kantor 1999; Mason et al. 2007). The US Food and Drug Administration (FDA) defines dietary supplements as a specific category of product independent of food or food additives (www.fda.gov). In Poland, Sweden, the Netherlands, and other EU countries, a dietary supplement is defined as a foodstuff intended to supplement a normal diet and is not intended to treat or prevent diseases. They are regulated under food law (not pharmaceutical). The European Consumers’ Organization BEUC calls for a clear legal framework to classify these products, which should consider the impact on human health and body, regardless of their physiological, nutritional, or health effects, as well as the safety of the proposed dose (www.beuc.eu). In China, dietary supplements are categorized under “health food” and defined as foods that claim specific health functions or provide vitamins and minerals to supplement the diet for specific groups of people. These products, considered “special foods”, are intended to help regulate body functions or supplement nutrients. They are not intended for therapy or treatment of diseases (https://www.ciprocess.com).

Weight loss, memory boost, easy sleep, stopping the aging process… Those are only a few promising food supplements offered (Fig. 1). According to the 2023 CRN Consumer Survey on Dietary Supplements, around 74% of adult Americans report taking supplements and more than half of the US population is regular supplement users (www.crnusa.org/2023survey). Some consumers use supplements to treat mild discomfort (e.g., echinacea for the cold), while others use them to control serious or chronic diseases (e.g., saw palmetto for benign prostatic hyperplasia, or glucosamine for arthritis) (Manning et al. 2021).

Fig. 1.

The main reasons why people take supplements (Bailey et al. 2013)

Some supplements can interfere with the effects of drugs or radiation in the body and reduce the effectiveness of treatment (Ambrosone 2019). For example, red clover may interfere with manner in which tamoxifen works in the body (www.cdc.gov). Moreover, St. John’s wort can decrease the effect of birth control pills or drugs for AIDS. It is important to implement an efficient system for monitoring and registering side effects, including interactions between supplements, drugs, and other products (Anadón et al. 2016; Sood et al. 2008). Another problem is androstenedione, which was used as a dietary supplement until it was placed on the federal list of controlled substances along with other steroids and precursor compounds under the Anabolic Steroid Control Act of 2004 (www.congress.gov/bill/108th-congress/senate-bill/2195/all-info).

Although supplements cannot be sold for the treatment or prevention of disease, they are often used as such. People often choose to self-treat illnesses without consulting a specialist, incorporating various dietary supplements into their regimen (Fig. 2). The more supplements people consume, the more serious the consequences can be, both good and bad. One problem is incorrect information about product ingredients on packaging, which can pose a health risk. Furthermore, few commonly used claims about supplements have been confirmed by scientific research (Dateshidze et al. 2023). Most of this information is related to the potential health benefits of consumption.

Fig. 2.

Types of dietary supplements used by US surveyed users based on age (https://stacks.cdc.gov/view/cdc/101131)

Food supplements should contain purely substances of proven safety and only in the recommended harmless doses. However, this rule is not being followed. The dietary supplement market faces several major challenges: a lack of consumer awareness of the regulations governing the sale of supplements, the safety and potential effects of their use, insufficient institutional oversight, and a lack of appropriate regulations to ensure safety. This article provides a pictorial analysis of the regulations and institutional solutions currently in place in the dietary supplement market. Many experts believe that raising public awareness of broadly defined human health and healthy eating is crucial, given the vast market for dietary supplements and the increasing popularity of their consumption. The information provided here is a starting point for discussion on the quality of dietary supplements and their effectiveness in the context of global mass production and uncontrolled consumption.

Statistical data

Many people assume that vitamins and dietary supplements improve health, alleviate diseases, and prevent aging. The estimated size of the supplement market has grown from 4000 in 1994 to more than 55,000 in 2012, and about half of the adults in the USA have used at least one nutritional supplement in the month (Geller et al. 2015). As of 2017–2018, it was reported that more than 57% of US adults used at least one dietary supplement in the past 30 days (https://stacks.cdc.gov/view/cdc/101131). Until the mid-1990s, the most widely used were multivitamin/mineral supplements; however, in recent years, there has been a huge boom in products that were once reserved for specialist stores and have become generally available. Their sales have increased as availability has increased.

It is worth mentioning that the dietary supplements market has developed in recent years because of the COVID-19 pandemic. The Council for Responsible Nutrition (CRN) survey reported increases in the use of some supplements, such as multivitamins and vitamins C and D, of 59%, 44%, and 37% among US citizens aged between 18 and 35 years. In Europe, dietary supplement sales have also grown significantly since 2020. It is estimated that sales of supplements exceeded 1,6 billion Euro in Italy and more than 100 million Euro in other European countries (such as Germany, UK, France, or Poland) (Djaoudene et al. 2023).

It is estimated that the dietary supplement market will grow equally intensively in the coming years (Fig. 3). According to forecasts by Statista.com, the dietary supplement market is expected to be worth more than 300 billion $ by 2028 (www.statista.com/statistics/828514/total-dietary-supplements-market-size-globally).

Fig. 3.

Geographical distribution of dietary supplements market, the level of growth of the supplement sales market worldwide (Djaoudene et al. 2023)

Surveys indicate that the vast majority (93%) of supplement users in the USA reported purchasing their supplements from mass retailers. Of these, only 39% bought supplements in drug stores or pharmacies and 46% bought supplements in mass merchandisers, such as Walmart (Fig. 4). Twenty-five percent of purchasers received their supplements online, mostly from Amazon, which made up 77% of all online purchases. Only 5% of patients decided to buy dietary supplements from medical doctors or other healthcare professionals (Ambrosone et al. 2019; www.statista.com/statistics/308349/top-places-to-purchase-dietary-supplements-among-us-adults).

Fig. 4.

Places to purchase dietary supplements among US adults in 2023 (www.statista.com/statistics/308349/top-places-to-purchase-dietary-supplements-among-us-adults)

With the recent development of social media and the occupation of “influencers”, “influencer” marketing has had a significant impact on customers’ purchasing decisions, including dietary supplements (Fig. 5). Due to the specific relationship between influencers and their followers, there is a noticeable increase in purchasing supplements based on an individual’s opinion. Consumers often decide to trust influencers based on their personal experiences with products, rather than healthcare professionals. A survey performed by Open Evidence for BEUC showed that over half of the respondents reported buying various products recommended by influencers (www.beuc.eu).

Fig. 5.

Percentage of people purchasing supplements recommended online by influencers (www.beuc.eu)

The increase in trust towards influencers when buying products online is noticeable in all age groups (Or et al. 2019). However, it is especially significant among children and teenagers, because they are the target audience of influencers. Children and teenagers are most prone to influence, which can be especially dangerous with products that may affect health, such as dietary supplements that support weight loss or improve concentration (Barretto et al. 2024; www.beuc.eu).

The data on dietary supplement consumption varied considerably (Fig. 6). The largest market for dietary supplements is North American countries, especially the USA. In 2023, the US dietary supplement market size was estimated at $53,58 billion, and it is expected to grow at a compound annual growth rate of 5,7% from 2024 to 2030. According to forecasts, the US dietary supplement market size will be around $78,94 billion. The largest share of the supplement market was for energy and weight management supplements, accounting 67,5% of the market share. It is estimated that 15% of US adult citizens have used a weight-loss dietary supplement at least once in their lifetime, with usage reported by more women (21%) than men (10%). Americans spend approximately $2,1 billion on weight loss supplements (Blanck et al. 2007; www.grandviewresearch.com/industry-analysis/us-dietary-supplements-market-report).

Fig. 6.

Global dietary supplements market value in 2018 and 2020 with a forecast to 2026 (*) by region (www.statista.com/statistics/1264459/region-global-dietary-supplement-market)

Among cancer patients, it has been reported that the consumption ranges from 5 to 60%. Apart from industry analyses used for marketing purposes, the available data do not allow for an accurate estimate of the number of consumers. A report by the US Centers for Disease Control and Prevention found that about 40% of the US population uses dietary supplements, more often women and whites (www.cdc.gov/nchs/products/databriefs/db399.htm).

According to the US National Health Interview Survey, approximately 25% of 11,643 people were taking vitamin and mineral supplements daily. Of more than 2000 Americans, 12% reported taking herbal products and 5.5% reported taking vitamins. Herbs have been identified as one of the most commonly used remedies for allergies, insomnia, and digestive disorders, whereas vitamins are used for high blood pressure. The parallel use of herbal products and/or large amounts of vitamins is reported by nearly ⅕ of the 44% of adults taking prescription drugs (Fig. 7). In Canada, the supplement industry has quickly grown into a profitable business worth USD 17 billion annually. While manufacturers spend millions of dollars on marketing with the promise of a “miracle cure”, ignorance of the facts and potential risks can be confusing to consumers (Karbownik et al. 2019; McCann 2005).

Fig. 7.

The main categories of natural supplements used by US adults (in %) (Clarke et al. 2015)

China is the world’s second-largest dietary supplement market (https://www.ciprocess.com). This market is estimated to be worth over $30 billion by 2024, and is growing rapidly (by 6–8% annually), driven primarily by an aging population, growing health awareness, and the growth of the middle class. At the same time, the Chinese market serves as a base for many international brands operating through direct imports and local production.

A similar situation of growth in sales of supplements is observed in many other countries, including European ones (Fig. 8).

Fig. 8.

Sales value of dietary supplements and vitamins in Sweden recorded in 2017–2022 by category (www.statista.com/statistics/783512/sales-value-of-dietary-supplements-and-vitamins-in-sweden-by-category)

According to the 2023 CRN consumer survey, 92% of supplement users agreed that dietary supplements are essential for maintaining their health. More women (52%) used supplements than men (48%). Supplement consumption increases with age; 40% of survey participants were over the age of 55 years. Dietary supplements are also frequently used in richer households. When household income is $50 K or more annually, people are more likely to use dietary supplements (66%) than in poorer households (34%). More than 50% of the survey participants lived in suburban areas. The survey shows that most White Americans use supplements (78%) (www.crnusa.org/2023survey).

In 2022, 41% of Dutch adults used dietary supplements, according to the Healthy Lifestyle Monitor report by research firm Multiscope. This group spent a total of €1.6 billion on dietary supplements (www.multiscope.nl).

In 2017, the Polish Supreme Audit Office (NIK) presented a report that indicated that over 26% of respondents buy supplements online, and almost 7% in stores; in some supplements, ingredients harmful to health/life were found (Kowalska-Olczyk 2023; www.nik.gov.pl, www.egospodarka.pl).

In 2021, the supplement market in Poland was worth PLN 6 billion. According to the ARC Rynek survey, 64% of the adult Polish citizens were using supplements in 2020. During 2008–2017, the worth of the dietary supplement market in Poland rose more than three times – from PLN 1,7 billion in 2008 to PLN 4,4 billion in 2017. It is estimated that it will rise by 5% every year (Karbownik et al. 2019; https://pie.net.pl/blisko-%C2%BE-polakow-spozywa-suplementy-diety).

Legal bases and regulations

Consumers expect nutritional supplements to be inexpensive, readily available, and safe for consumption. However, the legislative history of supplements shows that a struggle is underway to strike a balance between these partially conflicting requirements (Łata 2022). Numerous reports of their falsification and contamination with dangerous compounds, toxic metals, drugs, pesticides, and pathogenic organisms have undermined consumer confidence. With many manufacturers producing thousands of products, it is very difficult to ensure their safety by enforcing existing regulations (Gershwin et al. 2010; Tuptuk and Hailes 2018; www.ftc.gov/system/files/documents/plain-language/bus09-dietary-supplements-advertising-guide-industry.pdf). Producers are currently responsible for ensuring high-quality products. Unfortunately, there are also products with few or no ingredients listed on the label (Harris et al. 2004; Starr 2015). An extensive review (including 67 studies and information from more than 232,000 healthy and sick people) assessed the results of tests on the effect of vitamins and bioelements on mortality. Mortality has not been shown to decrease in people taking supplements, and the results for vitamins A and E and beta-carotene suggest that they may increase this risk. Based on these results, there is a need for further research into the potentially harmful effects of consuming supplements that should be urgently formalized (Bjelakovic et al. 2012).

Dietary supplements as “special foods” are regulated by the Federal Food, Drug and Cosmetic Act (FFDCA). The Federal Trade Commission has the task of enforcing laws that forbid dishonest or deceptive acts or practices. Both institutions work together within a system governing the distribution of responsibilities (Czerwiński and Liebers 2019; www.ftc.gov). The DSHEA was introduced in 1994 as a separate class of foods and has accepted separate regulations for them (Khatcheressian 1999). Under the DSHEA, these products must be labeled as dietary supplements. Unlike medications, they are not intended to treat or prevent disease, even if they are made with similar ingredients. In the US, the supplement market is primarily regulated by the FDA. However, unlike medications, the FDA does not approve supplements for safety or effectiveness. It is the manufacturer’s responsibility to ensure the safety and proper labeling of their products (Harris et al. 2004; http://ods.nih.gov). In 2011, the Food Safety Modernization Act (FSMA) was signed, covering two main areas: supplement companies were exempt from hazard analysis and control requirements when strictly adhering to Good Manufacturing Practice (GMP), and standards for new dietary ingredients were established (Manning et al. 2021).

The FDA has established quality standards for supplements to prevent the wrong ingredient from being added, contamination, over-mixing with too much or too little of the active ingredient, and improper packaging and labeling of the finished product (Harris et al. 2004; http://ods.nih.gov). Post-marketing reporting of irregularities is only required for serious adverse events such as hospitalization, severe disability, or death. Most vitamin and mineral supplements are manufactured in accordance with the United States Pharmacopoeia (USP) guidelines, which control product quality in terms of concentration and purity. However, dietary supplement manufacturers are not legally bound by USP standards (Thakkar et al. 2020). In the case of supplements used by athletes, the International Olympic Committee (IOC) warns against contaminated or incomplete products, especially when it is uncertain whether the product contains a banned substance (Maughan et al. 2018; Kozhuharov et al. 2022; www.olympics.com/ioc/fight-against-doping).

A separate problem was the use of supplements containing plants. Parts of plants that are frequently used as ingredients in dietary supplements have been identified (in the USA regulated by the FFDCA of 1938, modified by the Health and Education Supplements Act of 1994), and the FDA outsourced to manufacturers to assign a specification for each of these components (AOAC 2013; www.fda.gov/food/dietary-supplements). Currently, state and local governments can introduce stricter legal regulations or stop selling harmful supplements. This is what Florida, Texas, and Ohio did after declaring deaths attributable to herbal ephedrine supplements (Charatan 2003; www.fda.gov).

The dietary supplement market in China is strictly regulated by the State Administration for Market Regulation (SAMR) and its delegated agency, the National Medical Products Administration (NMPA). The regulations require product notification or registration before being placed on the market, along with a declaration of the product category (http://samr.saic.gov.cn). Each category is subject to separate registration, and therefore the choice of regulatory framework influences the level of testing requirements, registration, duration, and associated costs.

In EU countries, dietary supplements must be labeled according to both European and national (Acts on Food and Nutrition Safety) regulations. European food market operators are responsible for ensuring that their products are safe and compliant with food law requirements before being placed on the market. Generally, there is no notification procedure for placing dietary supplements on the market, but food market operators are required to register them. The inspection includes determining the level of contaminants, including lead, cadmium, mercury, dioxins, and polycyclic aromatic hydrocarbons (PAHs), in accordance with the guidelines for their content in food.

The European Commission, which cooperates with the European Medicines Agency (EMA) and the European Food Safety Authority (EFSA), is responsible for creating similar regulations in the EU. In the case of products containing plants, the EMA has established a Committee for Herbal Medicinal Products, which deals with herbal medicines (Baraniak and Kania 2015). However, regulations on the safety of supplements in intra-EU trade vary and are mainly concerned with vitamins and minerals (https://food.ec.europa.eu/food-safety). This patchy regulatory framework leads to different safety standards and product evaluation strategies, creating confusion and unacceptable inequalities. The same product can be considered a “botanical food supplement” in one EU country and a “herbal medicine” in another country. The same substance may be sold in the same country as a dietary supplement and herbal medicine; for example, Valeriana officinalis is not on the list of botanicals used in supplements in Germany, whereas there are more than 2,000 products on the market containing valerate, known as herbal medicinal products (Baraniak and Kania 2015; Colombo et al. 2020; www.ema.europa.eu).

In Poland, products are assessed by the Office for Registration of Medicinal Products, Medical Devices and Biocidal Products, and dietary supplements are supervised by the Chief Sanitary Inspectorate (GIS) (Wojciechowski 2010; www.gov.pl/web/chief-pharmaceutical-inspectorate). To introduce a supplement to the market, it is sufficient to report it to GIS. There is no obligation to inform the package or leaflet regarding interactions with other drugs, food, or side effects. Owning to the lack of detailed regulations on substances found in dietary supplements, some raw materials are used simultaneously in medicines and supplements. However, the raw materials used in the production of supplements do not have to meet strict quality standards. Furthermore, the form and packaging of supplements are often similar to those of drugs. The ubiquitous advertising of these products and their frequent placement on store shelves may falsely suggest that the supplement is a medicinal product. The differences stem from the fact that supplement packaging must include the word “dietary supplement” and a note that the product should be kept out of the reach of children. In addition, information about the recommended dose for a day and warning not to exceed the recommended dose.

In the UK, most products defined as food or dietary supplements are subject to the Trade Descriptions Act of 1968, Food Safety Act of 1990, and Food Information Regulation of December 2014. Foods that are not completely safe, and are not of the demanded quality, or are presented in a false manner are a criminal offense (Jurica et al. 2021). For example, under EU regulations, there is no explicit ban on the use of silver hydrolate or colloidal silver in dietary supplements (that claim to support the immune system). Therefore, each EU member state can decide, authorize, or prohibit the use of a substance in its territory. At the same time, dietary supplements containing silver are legally sold in the USA, with a warning to consumers that the product “may permanently turn the skin color to a bluish-gray” (Hadrup et al. 2018).

Reliable data on the consumption of dietary supplements in the EU is still insufficient. During a 5-year contract with the National Institutes of Health–Office of Dietary Supplements through the FDA, the Association of Official Agricultural Chemists (AOAC) validated methods for analyzing supplement ingredients. The final guidelines were adopted by the AOAC Official Methods Board and Board of Directors in December 2002 (AOAC 2013). New organizations, such as BEUC, are being established to establish rules ensuring the same level of consumer protection in different countries, combat counterfeiting of dietary supplements, set limits to avoid the risk of overdosing and selling useless products, provide consumers with reliable information, and monitor and report side effects of supplements, including those containing plant-based ingredients (Harris et al. 2004; www.beuc.eu).

The Netherlands has introduced a dietary supplement reporting system (BuRO), which aims to reduce the risks associated with their uncontrolled use (https://english.nvwa.nl). In recent years, the BuRO has assessed the risks associated with various dietary supplements, taking into account cases in which their use led to serious health consequences.

Considering the above information, steps should be taken to harmonize regulations and require supplement manufacturers to register products, collect data, and analyze reports on an ongoing basis, as well as report adverse events to designated organizations. Proper education of healthcare professionals and consumers is also crucial, as is international cooperation to develop a common safety program for dietary supplement ingredients, including herbal ones (Mosadeghrad 2014; Stohs and Preuss 2017).

Opinion related to dietary supplements

Growing social awareness means that people pay more attention to caring for their health. In this article, we want to draw attention to the fact that some dietary supplements are not helpful, and some can even be harmful (Chen et al. 2019). The following are the most common formulas associated with taking supplements (Harris et al. 2004; Willett et al. 2013). It must be noted that not all of these are true.

“If little is good, more will be better”. Consumers often assume that they can take supplements without restrictions because they are sold over the counter. However, they should remember that each active ingredient requires a specific daily dose. It is essential to remember that everything can become harmful; the effect of a substance is based on the dose used.

“Natural is safe”. Often, information about supplements says that they are “completely natural”, but some of the most toxic substances in the world are natural (e.g., mushrooms or plants). Supplements containing plant material (ginger, Ginkgo biloba, echinacea, and more) comprise many different chemicals that can be helpful, harmful, or poisonous. Particular parts of plants (roots, stems, flowers, leaves, and juices) may vary; for example, dandelion root is a laxative, and leaves contain a compound that increases urine output.

“It’s been used for hundreds of years, so it must work”. Substances used in traditional or folk medicine for thousands of years are not necessarily safe. No side effects were observed; however, after years of use, it was noticed that, for example, they increase the risk of chronic diseases.

“There is no harm in taking dietary supplements along with your regular medications”. The use of dietary supplements and drugs is not necessarily safe. Most manufacturers of supplements do not test for all possible interactions; therefore, the risks are unknown.

“If it could cause harm, it wouldn’t be sold”. Owning to the regulations in force, the safety of dietary supplements rests only with the manufacturer.

There are several studies on the effects of supplements on disease, but the results are not convincing; for example, studies of cardiovascular diseases concerned the problem of whether taking multivitamins reduces the risk of heart attack, stroke, and death, and the observed effects may be accidental. There are many ideas about supplements for treating cancer and other chronic diseases, but they do not provide reliable information (Willett et al. 2013).

Based on the expert opinions submitted to the FDA, several rules have been identified regarding the risks associated with consuming supplements (www.fda.gov, https://experiencelife.lifetime.life):

• Supplements are not risk-free; for example, reports of serious health problems of people consuming a vitamin preparation produced by Indo Pharma from the Dominican Republic,

• Some supplements contain active ingredients such as drugs; since 2008, over 400 such products have been withdrawn from the market (including sildenafil, tadalafil, or sibutramine),

• too high doses of active ingredients may cause dangerous ailments, for example, fat-soluble vitamins (A, D, E, K),

• It cannot rely on labels. There are no requirements for warning information on supplement packaging, with the exception of iron (potentially fatal overdose in children),

• supplements cannot be advertised to heal ailments,

• Be careful with natural products. Shops selling medicinal plants and various artifacts do not inform the consumer about the potential dangers,

• However, there is no proven protection against serious diseases. For example, research fails to confirm that omega-3 acids and antioxidants reduce the risk of heart disease and cancer,

• pills may irritate the esophagus; choking after taking the pill is a common problem,

• “Natural” products are for everything. Synthetic mixtures corresponding to plants cannot be classified as natural food supplements, and the FDA issued warning letters to manufacturers and distributors of dimethylamylamine (DMAA) products advertising them as natural stimulants, stating that synthetic DMAA is not safe and cannot constitute a dietary form,

• If an individual is following a well-balanced diet, it may not be necessary to take supplements.

Unfortunately, ubiquitous advertisements suggest that dietary supplements have medicinal properties or are essential elements in a person’s daily diet (Harasimiuk 2011; Wirt and Collins 2009). Often, there is a phrase indicating that supplements provide quick improvement in health. The promotion of these products using umbrella branding has become increasingly popular. This process involves making products from different categories similar to each other; for example, introducing a medicinal product under a given brand and then introducing a dietary supplement under a very similar brand, which, as we already know, is not a medicine.

Risks associated with the use of dietary supplements

With the increasing number of dietary supplements consumed, new challenges have arisen in food science and safety. There is a lot of misinformation, and it can be difficult to obtain reliable information regarding safe use and potential dangers. FDA news shows that the number of reports on the side effects of supplements continues to rise (2010: 1009 reports; 2012: 2844 reports) (www.fda.gov/drugs). In 2019 alone, dietary supplements, herbal preparations, and homeopathic treatments caused almost 70 000 calls to US poison control centers (Rao et al. 2017). Of these calls, more than 7000 (which is more than 10% of the cases) people need to undergo treatment at health care facilities (Harris et al. 2004; Camire and Kantor 1999). Of the emergency room visits, 65.9% were for herbal or nutritional supplements and 31.8% were for micronutrients. Weight loss or energy products accounted for 71.8% of side effects. 58% concerned people aged 20 to 34 years, and in adults over 65 years of age, problems after taking supplements occurred in 37.6% (83.1% after consuming micronutrients (Geller et al. 2015; www.govinfo.gov/content/pkg/GOVPUB-HE-PURL-gpo68585/pdf/GOVPUB-HE-PURL-gpo68585.pdf) (Fig. 9).

Fig. 9.

Number of emergency department visits due to adverse events associated with dietary supplement use in the USA in 2004–2013, by gender and product category (Geller et al. 2015)

The health problems linked with dietary supplements fall into three principal categories: direct toxicity (e.g., high doses of vitamin A taken during pregnancy and higher rates of cranial neural crest birth faults), interactions (synergistic effects, intoxication, or inactivation, e.g., St. John’s Wort used to boost mood could reduce the effectiveness of antiviral specifics used to cure HIV infection), and contaminations (e.g., The California Department of Health reported that 32% of 260 Asian herbal products included lead or arsenic) (Or et al. 2019; Mikulski et al. 2017; Washam 2006). Some supplements contain undeclared admixtures; for example, 33% of the analyzed ginseng products did not contain panaxosides (active ingredient) and 67% had variable content (Harris 2000). The bioavailability of the ingredients is an important issue, and sometimes it is sufficient to produce a pharmacological effect of 1% (e.g., curcumin and inflammation) and sometimes not (e.g., curcumin and cancer) (Tabanelli et al. 2021). Therefore, the term “poor bioavailability” in the opinion on supplements may be misleading (Aqil et al. 2013). Toxicity of supplements can occur from over-consumption of minerals, such as iron, magnesium, selenium, or zinc, which can generate digestive problems; too much calcium might prompt kidney stone generation, and high manganese levels can lead to neurotoxicity. Supplements can contain proteins, which, if supplied in excess, may lead to weight gain (Harris et al. 2004; Glicksen et al. 1990). Too high doses of vitamins can also cause more harm than good (Willett et al. 2013; Wooltorton 2003). Research on vitamin A shows that doses of more than 3000 IU/day may cause liver damage, reduced bone strength, headache, and birth defects. Beta-carotene has been found to increase the risk of lung cancer in heavy smokers and in people exposed to asbestos. An overdose of niacin (vitamin B₃) can cause skin flushes or lead to a loss of feeling in the arms and legs, and levels of vitamin C more than 1000 mg/day can induce abdominal ache and diarrhea (www.nhs.uk). A consumer organization checked the composition of 29 multivitamin and multimineral products sold in the USA and Canada, eight of which did not meet the label requirements, and 12 contained overdoses of active substances (Willett et al. 2013). The Medicines and Healthcare Regulatory Agency (MHRA) publishes warnings about certain products sold via the Internet. Many compounds in popular weight-loss products have side effects; for example, sibutramine was found in two Chinese herbal supplements (www.nhs.uk).

The consumption of supplements by children is an additional problem because they are not subjected to proper testing for the presence of undesirable substances, which is not required by law. For example, the use of a sleep aid supplement (containing L-tryptophan) was associated with an epidemic of eosinophilia and muscle pain syndrome (EMS) (the Centers for Disease Control and Prevention reported 1,500 EMS accidents, including 37 deaths). The FDA requires manufacturers to withdraw such products from the market (Glickstein et al. 1990; Kamb et al. 1992; www.health.ny.gov/regulations/index.htm).

Obesity is a major health problem among others in the UK and USA. For this reason, customers often reach for slimming supplements and miracle pills (Lenz and Hamilton 2004; Rios-Hoyo and Gutierrez-Salmean 2016). Studies have shown that of 164 proven weight loss products labeled as 100% natural, more than 40% were contaminated. Another study found that 43% of dietary products used for weight loss contained oxilofrin, a pharmaceutical stimulant used to raise blood pressure, at concentrations five times the maximum daily dose (Cohen et al. 2017).

Another example is synephrine, which is naturally present in citrus fruit. In 2009, the French Food, Environment and Health and Safety Agency reported 13 cases of cardiovascular problems, liver damage, and neurological damage resulting from the use of dietary supplements containing synephrine (www.anses.fr/en/content/dietary-supplements-weight-loss-containing-p-synephrine). Athletes widely use dietary supplements. Some offer the opportunity to improve performance, while others, such as prohormones, are expected to help increase muscle mass or strength, but unfortunately can have negative health effects. Some products may be contaminated with prohibited substances, as demonstrated by drug testing (Maughan et al. 2011). Glucosamine and chondroitin sulfate are native substances that are produced by the body. Research suggests that it is not beneficial to consume them as supplements for osteoarthritis (www.nhs.uk).

The use of supplements can be dangerous, especially in patients with cancer. Some dietary supplements can cause severe skin sensitivity and, therefore, harmful reactions to radiation treatment. Moreover, patients receiving chemotherapy are prone to side effects (Harris et al. 2004; www.cancercouncil.com.aus). Some people believe that it is impossible to overdose on vitamins, and taking high doses may help strengthen the immune system. Apricot kernels (amygdalin) have been promoted as an anti-cancer therapy; however, studies have shown that they are converted into poisonous cyanide in the human body. Shark cartilage has been used as an anti-cancer drug, but studies have not confirmed this effect (Chiou et al. 2011).

As mentioned above, herbal and plant supplements pose a significant problem (Ekor 2014; Hassen et al. 2022; Zakaryan and Martin 2012). Many interactions between herbal products and conventional drugs have been reported. For example, people using anticoagulants should not take “Angelica sinensis” (Dong Quai) supplements, and women using oral contraceptives should avoid “Hypericum perforatum” (St. John’s wort). Plant products are complex mixtures of various chemical compounds that are affected by differences in growth, harvesting and storage conditions, as well as by different extraction procedures (Gershwin et al. 2010). Despite the global history of traditional medicine, the World Health Organization (WHO) claims that “counterfeit, poor quality or falsified herbal products in international markets pose a serious safety risk” (Mullaicharam 2011; www.who.int). The standards of manufacturers and distributors vary widely in terms of product quality. In 2013, researchers in Toronto presented the results of studies on 44 herbal products sold in the USA and Canada, labeled as containing single herbs. Only 48% contained the herb listed on the label, and more than half of the compounds identified in the product were not listed on the label (Harris et al. 2004). In other studies, only 16% contained the right ingredients, more than 30% contained a different plant, one-third contained various “fillers”; e.g., Ginkgo was contaminated with black walnut leaves, which can cause lung or skin cancer (Mei et al. 2017). The Occupational Pension Schemes Survey collects information on the market for products containing geranium extract (DMAA). In 2013, the FDA declared these supplements illegal; however, many are still available (www.opss.org). Researchers in Australia have recognized that heavy metal poisoning from Indian Ayurvedic supplements is a well-known health problem (Gunturu et al. 2011). A few years ago, the FDA warned consumers to immediately stop using products containing aristolochic acid because of permanent kidney damage or urinary tract cancer (Wooltorton 2003; Wheatley and Spink 2013). Some consumers believe that using certain substances for hundreds of years is safe and effective. However, this is problematic as herbal products vary widely and can cause side effects that may appear slowly. The current standards of treatment differ significantly from traditional ones, for example, the use of ephedrine (Cho et al. 2024). There are also genetic differences related to the ability of one population to tolerate a particular substance that poses a risk to another group or the general population (Madian et al. 2012). Plants can interact with medications (prescription, OTC, vitamins, etc.); for example, ginkgo taken with ibuprofen can lead to excessive bleeding, and garlic may enhance the adverse effects of anticoagulant and antiplatelet drugs. Moreover, some supplements can reduce the absorption of others; for example, supplemental iron taken simultaneously with zinc supplements can reduce the absorption of the latter. Herbs are also not advised for people with reduced immunity (the elderly or infected with HIV), with kidney or liver disease, undergoing surgery, pregnant and lactating women, and children under six years (Bellows and Moore 2013).

Most individuals who experience side effects, diseases, or interactions while taking supplements do not report such cases (Budnitz et al. 2006; Nahin et al. 2009). This means that the available reports have very low estimates of real cases (Geller et al. 2015; Ross et al. 2012).

To eat or not to eat?

People want a positive and healthy sense of self-worth, which is a strong motivation for healthy behavior. There are many benefits of using dietary supplements, and therefore there are many reasons why people decide to use them daily (Table 1). However, the belief in the effectiveness of supplements cannot be the strongest. Consumers should be made aware of the risks associated with their consumption (Ang et al. 2023; Lenssen et al. 2020; www.health.harvard.edu) especially people taking medications on a regular basis, women taking birth control pills, people with kidney, liver or heart problems, people infected with HIV, people after organ transplants, etc. (Harris et al. 2004; Diekman et al. 2023; Khubchandani and Batra 2024).

Table 1.

Percentage of most important reasons for using dietary supplements among US adults by gender (2007–2010) (Bailey et al. 2013)

Reason	All adults (n = 5514)	Men (n = 2450)	Women (n = 3064)
To improve overall health	45.0	46.4	43.9
To stay healthy	32.8	32.8	32.8
For bone health	25.2	11.3	35.8
To supplement the diet	22.0	20.8	23.0
To prevent health problems	20.4	20.6	20.2
For heart health	15.1	17.6	13.2
To boost immunity	14.5	15.8	13.4
To prevent arthritis	12.4	12.2	12.5
Enhanced energy	10.8	9.9	11.4
Skin health	5.1	3.8	6.0

The British Nutrition Foundation recommends that people interested in healthy eating speak to competent healthcare professionals (such as doctors, pharmacists, and dieticians). This also applies to people before starting the use of a new product (drug or supplement) or planned treatments (Harris et al. 2004; www.nhs.uk).

The information presented in the article clearly indicates excessive interest (sometimes even mindless fascination) in dietary supplements that offer a “long and healthy life” (striving for longevity without effort) in a simple and uncomplicated way. However, it should be noted that the production of dietary supplements is aimed at quick profit. It is not the responsibility of the producers to generate costs for quality testing of the raw materials used, as well as testing for potential multiple interactions with other foods and/or drugs. Therefore, the decision to consume a specific supplement should be made with full awareness of the client/patient.

Conclusions

There are many reasons a person decides to start taking supplements. A product may be recommended by friends or family, and someone can rely on opinions published in the media. However, the information obtained is not always reliable. Consumers may not understand that scientific results should be considered more reliable than, for example, surveys. Unfortunately, only a few legal regulations govern the production and distribution of supplements. This situation leaves many unknowns regarding its safety, composition, contamination, and effectiveness. Dietary supplements should undergo a control process similar to each drug, assessing possible side effects or interactions such as allergies, various diseases, interactions, and likely duplication of treatments. When thinking about using a supplement, consumers should be used to asking professional questions and conducting a health check before making a purchase. They should be made aware of the risk of interactions of dietary supplements with drugs and/or other substancespresent in food and/or other supplements, and the possibility of adverse effects, including toxic effects, constituting a threat to health or life. The growing popularity of dietary supplements should force the necessary research on optimal doses and interactions, and lead to the identification of links between supplementation of healthy people and the prevention of certain diseases in people of different sexes and ages. In summary, the best recipe for health is not supplements, but a healthy lifestyle that includes a balanced diet and the right amount of physical activity. It is therefore necessary to develop standards for verifying the quality of dietary supplements, taking into account not only the content of ingredients in the product but also the ability to release the active substance from the finished form. Only comprehensive actions can ensure the occurrence of the product’s effect, which is very important for the good of the consumer.

Future studies

This manuscript aims to present the scale of the problem related to the quantity, quality, and availability of consumed supplements, without focusing on one selected market of these products. We believe that this topic should be discussed in every possible way to reach (even by repeating certain information) the widest possible group of potential clients and professionals who can explain the problem to their patients. Due to the increasing information that we consume too much and often thoughtlessly, supplements can significantly and uncontrollably affect, for example, ongoing therapies.

In virtually all countries, there are reasons to be concerned about the safety of dietary supplements. Their composition is often unknown, and distribution regulations are very limited. In reality, national authorities have little power to enforce existing regulations. Therefore, our study includes information from several countries where such analyses were conducted, and the obtained data is available.

Future research should aim to verify the quality of dietary supplements available on the market, both in pharmacies, stores, and online. Thorough quality control should also apply to food, especially supplements, and document their potential interactions with medications, beverages, or food. Analyzing the presentation of dietary supplements on social media and new legal regulations introduced in virtually all countries and by international organizations will also be crucial. Further research is equally necessary to identify potential contaminants and identify additional ingredients, which are often missing from the ingredients declared on packaging. Identifying these compounds is crucial for product quality and consumer protection.

Author contributions

All authors wrote the main manuscript, text and table. M.S. and M.B. overviewed the selection of the literature. M.D. prepared figures. The authors confirm that no paper mill and artificial intelligence was used.

Funding

No funding was received.

Data availability

All data needed to evaluate the conclusions in this article are included in the article. Additional data related to this article may be requested from the authors.

Declarations

Competing interests

The authors declare no competing interests.