The use of herbal and dietary supplements for COVID-19 prevention: A survey among the public in a Malaysian suburban town

Abstract

Introduction

The spread of the novel coronavirus disease (COVID-19) may lead people to seek preventative measures. The use of herbal and dietary supplements (HDS) may have become prevalent during the COVID-19 pandemic. This study aims to identify the prevalence, predictors, and patterns of HDS use for COVID-19 prevention in a sample of the general public in a suburban town in Malaysia.

Methods

An online cross-sectional survey was conducted between May and June 2021 involving adults ≥ 18 years old. Data on the self-reported use of HDS for COVID-19 prevention were collected. Logistic regression analysis was conducted to determine the predictors of HDS use.

Results

Overall, 41.9 % (168/401) reported using HDS to prevent COVID-19. Multivariate analysis showed that HDS users were more likely to be individuals ≥ 40 years old (adjusted odds ratio [aOR] = 1.774, 95 % confidence interval [CI] = 1.016 – 3.098), and to have had a history of HDS use prior to the pandemic (aOR = 19.378, 95 % CI = 5.901 – 63.639). Most HDS users referred to social media or websites (66.7 %, 112/168) for HDS information. Approximately half of them had consulted either pharmacists or doctors about their HDS use.

Conclusion

HDS use to prevent COVID-19 was common among the respondents. Several issues - such as the concurrent use of HDS with conventional medications, the use of unreliable sources of information, and the lack of consultation with healthcare providers (HCPs) - indicate that HCPs should be more proactive in their consultative and information-providing roles regarding HDS use.

1. Introduction

In Malaysia, coronavirus disease (COVID-19) was first identified on January 25, 2020, and involved three imported cases from China (Elengoe, 2020). Within less than a month, the first case of COVID-19 among locals was reported, marking the start of community transmission in Malaysia (Shah et al., 2020). Since then, Malaysia has experienced several waves of the pandemic that varied in terms of severity and extent. As of July 2022, approximately 4,600,000 cases of COVID-19 had been reported in Malaysia (Malaysia, 2022). Since January 2020, COVID-19 has caused approximately 36,000 deaths in the country (Malaysia, 2022). To curb the outbreak, the Ministry of Health, Malaysia (MOHM) initiated the national vaccination program in February 2021 with the aim of vaccinating at least 80 % of Malaysian citizens by February 2022 (World Health Organization, 2021).

Recent data has shown that more than 98 % of adults in Malaysia have received at least two doses of a COVID-19 vaccine, and almost 70 % have received a booster dose (Malaysia, 2022). In April 2022, the country transitioned from the COVID-19 pandemic into an endemic phase. However, since the declaration of endemic status, the country has seen occasional fluctuations in the cases of infections and deaths, as well as the emergence of new variants of the virus (Dyer, 2021). To date (July 2022), approximately 3000 daily cases of COVID-19 are being reported in the country (Ministry of Health Malaysia, 2022). Thus, the Malaysian health authorities continuously emphasise the importance of good personal hygiene (e.g. frequent handwashing with soap and water, and the use of hand sanitiser), the use of face masks, the practice of respiratory etiquette, as well as physical distancing (Shah et al., 2020).

In addition to good personal hygiene practices, people may take extra preventative measures to prevent themselves from being infected such as by consuming herbal and dietary supplements (HDS) (Lordan et al., 2021). In Malaysia, the use of HDS was already prevalent before the pandemic. Studies conducted in Malaysia between 2014 and 2019 showed that the use of HDS was common among the general public and patients with chronic diseases such as hypertension, diabetes and dyslipidaemia (Loo et al., 2020, Teow et al., 2021, Wahab et al., 2021, Zaki et al., 2018). Data from a nationally representative sample of the Malaysian Adults Nutrition Survey (MANS) 2014 showed that 28.1 % of the survey participants used vitamin/mineral supplements (Zaki et al., 2018).

Since the beginning of the pandemic, HDS have been frequently advertised as products that can enhance immunity and protect people from COVID-19 (Günalan et al., 2021). Although there is limited evidence that HDS are effective in preventing COVID-19, an increase in HDS demand has been observed during the pandemic (Hamulka et al., 2021), resulting in skyrocketing sales of these products (Grebow, 2020). In a recent survey among 632 Hong Kong residents, the prevalence of herbal supplements (HS) and dietary supplements (DS) use during the pandemic was 19.3 % and 25.3 %, respectively (Lam et al., 2021). In another study conducted in Saudi Arabia, 22.1 % of the respondents reported using HDS to prevent infection (Alyami et al., 2020). The aggressive marketing of HDS products (especially those claimed to boost immunity) in the media may influence the public to use HDS to protect themselves against COVID-19 (Wagner et al., 2020). Based on data and observations from other countries (Alyami et al., 2020, Hamulka et al., 2021, Lam et al., 2021), the use of HDS for the prevention of COVID-19 among the Malaysian population could be prevalent.

The prevalence and trends of HDS use for COVID-19 prevention are worth investigating. These trends could provide valuable information for healthcare providers (HCPs) which would allow them to remain updated on the common HDS being used or sought by the public for the prevention of COVID-19, thus giving them the confidence to effectively communicate with their patients about the topic. Additionally, due to the abundance of misleading information regarding the use of HDS in preventing COVID-19 (Adams et al., 2020), HCPs with up-to-date awareness and knowledge about the issue can provide critical education and unbiased information about HDS to ensure patient safety and public health (Marwitz, 2021).

Thus, this study aimed to identify the prevalence and predictors of HDS use for COVID-19 prevention, as well as investigate the characteristics of HDS use in a sample of the general public in a suburban town in Malaysia. The findings could help HCPs, researchers, and other relevant stakeholders to enhance their understanding and awareness of the use of HDS for the prevention of COVID-19 among the local population. The data may help in developing strategies to promote the safe use of HDS among the public.

2. Methodology

A cross-sectional study was conducted over four weeks from May 23 to June 19, 2021, in a suburban town in Malaysia. This study was approved by the Research Ethics Committee of Universiti Teknologi MARA (UiTM), Malaysia (REC/04/2021[UG/MR/247]). The study procedures and results are reported according to the Checklist for Reporting Results of Internet E-Surveys (CHERRIES) (Eysenbach, 2004). The CHERRIES includes a checklist of important criteria for conducting online surveys. Adherence to the checklist ensures the complete reporting and descriptions of an online survey. A summary of the reporting of the present study, based on the CHERRIES, is available in Appendix A.

2.1. Study site and sample population

This study was conducted in Puncak Alam, a main suburban township in Kuala Selangor District, State of Selangor, Malaysia. The participants included those who identified themselves as residents of Puncak Alam, were at least 18 years old, and could understand the written Malay language. The sample size was calculated using the Raosoft© sample size calculator (Raosoft, 2014). A sample size of 377 was recommended with a margin of error of 5 %, a confidence interval of 95 %, and a response distribution of 50 % for an approximate total population of 20,000 adults in Puncak Alam.

2.2. Survey instrument

The survey instrument was adapted from a previous study that investigated the use of HDS among the elderly in Puncak Alam (Wahab et al., 2021). For this study, HDS refers to HS and DS that are taken orally in crude form or as pharmaceutical formulations such as pills, capsules, tablets, powder, or liquids. HS refers to plant materials/substances or plant-containing products, whereas DS refers to products containing dietary ingredients such as vitamins, minerals, amino acids, and other dietary substances (e.g. enzymes, organ tissues, glands, metabolites, extracts, and concentrates) (Wahab et al., 2019b, Wahab et al., 2021).

The questionnaire was developed in Malay, the national and official language of Malaysia. The questionnaire consisted of three sections (Appendix B). The first was completed by all the respondents, whereas the second and third were only answered by HDS users and non-HDS users, respectively. The first section of the questionnaire collected demographic data (gender, marital status, ethnicity, age, education level, history of chronic illness, use of prescription and over-the-counter [OTC] medications, etc.). This section also sought information on the respondents’ use of HDS to prevent and/or treat diseases or to maintain health before the pandemic, as well as their current use of HDS to prevent COVID-19.

In the second section of the questionnaire, respondents using HDS for COVID-19 prevention were asked to indicate, in relation to these HDS, the type/s used, their perceptions of the reasons for use, their frequency of use, and their source/s of information and obtainment. To understand the respondents’ experience of HDS use for COVID-19 prevention, they were asked to indicate their level of agreement on whether they believed that HDS had enhanced their body immunity system, for which a five-point Likert-type scale was used ranging from 1 = strongly disagree to 5 = strongly agree. They were also asked if they had experienced any adverse effects (AE) from HDS use by indicating “never”, “had mild AE”, “had moderate AE”, or “had severe AE”. Finally, the users were requested to indicate whether they had consulted any HCPs (i.e. doctors or pharmacists) about their HDS use for the prevention of COVID-19. The third section was answered by the respondents who had not used HDS to prevent COVID-19. They were asked to indicate their perceived reasons for their non-use of HDS for COVID-19 prevention.

The questionnaire was reviewed by five senior pharmacy lecturers to ensure that each item was relevant and suitable. Minor amendments were made based on the inputs from the reviewers. Due to the movement control order enforced by the Malaysian authorities during the study period, the survey instrument was generated into an online survey using Google Forms, a free survey administration software. To pilot test the questionnaire, the link to the survey was provided to a conveniently sampled group of 10 adults residing in Puncak Alam. The pilot test revealed that the questionnaire items were clear, and the use of Google Forms as the survey administration tool was feasible. The online survey took approximately 10–20 min to complete. The responses from the pilot testing of the questionnaire were not included in the final data analysis.

2.3. Data collection

The survey was distributed and collected using Google Forms. Google Forms online questionnaires can be shared using other online platforms. The survey uniform resource locator generated by the web link collector allowed respondents to access, answer, and submit the survey. To distribute the questionnaire, a convenient, non-probability sampling method was utilised in which the survey link was sent to the investigators' associates, while it was also shared to local online community groups through social media applications such as Facebook, WhatsApp, and Telegram. Respondents were encouraged to forward the survey link to their contact groups.

The first page of the online questionnaire provided a brief description of the study, including the objectives, the estimated time needed to complete the survey, and the contact details of the researchers. The respondents were asked to provide honest answers and informed that their completion of the questionnaire indicated their consent to participate in the study. Participation in the study was voluntary, and the respondents were offered anonymity and confidentiality. They could respond only once to the survey and were provided with no incentive.

2.4. Statistical analysis

All the statistical analysis was conducted using IBM SPSS version 23. Continuous data were presented as mean and standard deviation (SD), whereas categorical data were presented as frequency and percentage. Univariate and multivariable logistic regression analyses were used to determine the predictors of HDS use for the prevention of COVID-19. Odds ratios (ORs) and 95 % confidence intervals (CI) were reported for the logistic regression analysis. Statistical significance was established if the P-value was < 0.05.

3. Results

At the end of the study period, 565 complete questionnaires had been received. One hundred and sixty-four respondents were not Puncak Alam residents and were therefore excluded from the study. Thus, the valid response rate was 71 % (401/565). The sample size met the recommended minimum size for the study. As shown in Table 1, most of the respondents were female (72.6 %, 291/401), married (66.1 %, 265/401), and currently employed (67.8 %, 272/401), while most had tertiary education (82.5 %, 331/401). Less than 20 % of the respondents had at least one chronic illness (18.7 %, 75/401) or were using any conventional medications (16.5 %, 66/401). Only 13.5 % (54/401) had received at least one dose of a COVID-19 vaccine. The majority (84.3 %, 338/401) had a history of HDS use before the pandemic.

Table 1.

Demographic information of the respondents.

Demographic factor		All participants (n = 401) n (%)	HDS users (n = 168) n (%)	Non-HDS users (n = 233) n (%)	Univariate		Multivariate
					Odds ratio (95 % CI)	P	Odds ratio (95 % CI)	P
Gender	Female	291 (72.6)	127 (75.6)	164 (70.4)	1.303 (0.830–2.045)	0.249
	Male	110 (27.4)	41 (24.4)	69 (29.6)	Reference
Marital Status	Single	136 (33.9)	42 (25)	94 (40.3)	Reference		Reference
	Married	265 (66.1)	126 (75)	139 (59.7)	2.029 (1.311–3.139)	0.001	1.473 (0.805–2.693)	0.209
Age	18–39 years	235 (58.6)	84 (50)	151 (64.8)	Reference		Reference
	> 40 years	166 (41.4)	84 (50)	82 (35.2)	1.841 (1.229–2.760)	0.003	1.774 (1.016–3.098)	0.044
Education level	Secondary school or below	70 (17.5)	34 (20.2)	36 (15.5)	Reference
	University education	331 (82.5)	134 (79.8)	197 (84.5)	0.720 (0.429–1.208)	0.214
Employment status	Employed	272 (67.8)	120 (71.4)	152 (65.2)	Reference
	Unemployed	57 (14.2)	25 (14.9)	32 (13.8)	0.990 (0.557–1.759)	0.972
	Students	72 (18)	23 (13.7)	49 (21)	0.595 (0.343–1.031)	0.064
Monthly income	No income	101 (25.2)	33 (19.6)	67 (28.8)	Reference		Reference
	< MYR 2000	51 (12.7)	20 (11.9)	32 (13.7)	1.269 (0.632–2.548)	0.503	0.899 (0.424–1.904)	0.781
	MYR 2000–4000	94 (23.4)	47 (28)	47 (20.2)	2.030 (1.136–3.629)	0.017	1.497 (0.761–2.945)	0.243
	> MYR 4000	155 (38.7)	68 (40.5)	87 (37.3)	1.587 (0.940–2.679)	0.084	0.829 (0.434–1.585)	0.571
Chronic illnesses	Yes	75 (18.7)	34 (20.2)	41 (17.6)	1.188 (0.717–1.969)	0.504
	No	326 (81.3)	134 (79.8)	192 (82.4)	Reference
Use of conventional medication	Yes	135 (33.7)	61 (36.3)	74 (31.8)	1.225 (0.806–1.861)	0.342
	No	226 (66.3)	107 (63.7)	159 (68.2)	Reference
COVID-19 vaccination status	At least 1 dose	54 (13.5)	18 (10.7)	36 (15.5)	0.657 (0.359–1.202)	0.173
	Never	347 (86.5)	150 (89.3)	197 (84.5)	Reference
History of using HDSa	Yes	338 (84.3)	165 (98.2)	173 (74.2)	19.075 (5.867–62.014)	< 0.001	19.378 (5.901–63.639)	< 0.001
	No	63 (15.7)	3 (1.8)	60 (25.8)	Reference		Reference

MYR, Malaysian Ringgit (MYR 1 ≈ USD 0.24); HDS, herbal and dietary supplements; COVID-19, Coronavirus disease 2019.

^aPrior to the COVID-19 pandemic.

3.1. Prevalence and predictors of HDS use for the prevention of COVID-19

As shown in Tables 1, 41.9 % (168/401) of the respondents had used at least one HDS to prevent COVID-19. Of the HDS users, 44.6 % (75/168) had used at least one HS, whilst 95.2 % (160/168) had used at least one DS. Univariate analysis showed that respondents who were married, aged 40 years old or above, had a monthly income of between MYR 2000 and MYR 4000, or had a history of HDS use before the pandemic were significantly associated with the use of HDS for COVID-19 prevention (Table 1). Multivariate analysis showed that respondents who were 40 years old or older were approximately twice as likely to use HDS for COVID-19 prevention (aOR = 1.774, 95 % CI = 1.016–3.098). A history of HDS use before the pandemic was significantly associated with the use of HDS to prevent COVID-19 (aOR = 19.378, 95 % CI = 5.901–63.639).

3.2. Perceived reasons among users and non-users for the decisions on whether to use HDS for COVID-19 prevention

Table 2 shows the perceived reasons for the respondents’ decisions on whether to use HDS for COVID-19 prevention. For the HDS users, the belief that HDS could enhance the body’s immunity (92.9 %, 156/168) was cited as the main reason for their HDS use for COVID-19 prevention. However, only approximately one-fourth of the HDS users cited the availability of evidence that HDS were effective for COVID-19 prevention as a reason for their HDS use.

Table 2.

Perceived reasons behind the decision about HDS use for COVID-19 prevention by users and non-users.^a

HDS users (n = 168) n (%)
HDS can enhance the immunity of the body.	156 (92.9)
HDS are safe to be consumed for COVID-19 prevention.	64 (38.1)
HDS have evidence of effectiveness in preventing COVID-19.	42 (25)
My family members suggested me to use HDS to prevent COVID-19.	41 (24.4)
HDS are easily obtained during the pandemic.	39 (23.2)
Non-HDS users (n = 233) n (%)
There is no evidence for the effectiveness of HDS to prevent COVID-19.	143 (61.4)
Not interested in using HDS for COVID-19 prevention.	74 (31.8)
Not sure how to use HDS for COVID-19 prevention.	54 (23.2)
HDS are not effective to prevent COVID-19.	44 (18.9)
The price of HDS is too expensive.	39 (16.7)

Respondents can provide more than one response and therefore responses do not add up to 100 %.

HDS, herbal and dietary supplements; COVID-19, Coronavirus disease 2019.

^aRespondents can provide more than one response and therefore responses do not add up to 100 %; only the five most cited reasons are presented (refer to Appendix D for the full list of reasons for not using HDS reported in the study).

For the non-HDS users, the majority cited the unavailability of evidence that HDS were effective in preventing COVID-19 (61.4 %, 143/233) as the main reason why they did not use the products. The other common reasons for not using HDS included a lack of interest (31.8 %, 74/233) and uncertainty about how to use HDS for COVID-19 prevention (23.2 %, 54/233).

3.3. Experiences of HDS use for COVID-19 prevention

3.3.1. Types and frequency of HDS use for COVID-19 prevention

Table 3 shows the characteristics of HDS use among the HDS users. The five HS used most frequently to prevent COVID-19 were garlic (16.1 %, 27/168), ginger (15.5 %, 26/168), green tea (13.1 %, 22/168), black seeds (13.1 %, 22/168), and turmeric (12.5 %, 21/168). The five DS used most frequently to prevent COVID-19 were vitamin C (79.8 %, 134/168), honey (44.6 %, 75/168), olive oil (26.8 %, 45/168), fish oil (23.2 %, 39/168), and calcium (17.9 %, 30/168). Almost 50 % (89/168) of the HDS users had used between two and five HDS products. The average number of HDS products used was 3.9 (standard deviation: ± 3.1) and the highest number reported in this study was 20. Of all the users, 60.1 % (101/168) used HDS daily to prevent COVID-19.

Table 3.

Details of HDS use for COVID-19 prevention (n = 168).

Characteristics	n (%)
Type of HDS used for COVID-19 prevention
Uses at least one type of herbal supplement	75 (44.6)
Uses at least one type of dietary supplement	160 (95.2)
Number of HDS used per user
1 product	39 (23.2)
2–5 products	89 (53)
6–10 products	33 (19.6)
> 10 products	7 (4.2)
Average (± SD); range	3.9 (± 3.1); range: 1–20
Herbal supplementsa
Garlic (Allium sativum)	27 (16.1)
Ginger (Zingiber officinale)	26 (15.5)
Green tea (Camellia sinensis)	22 (13.1)
Black seeds/Habbatus sauda (Nigella sativa)	22 (13.1)
Turmeric (Curcuma longa)	21 (12.5)
Cinnamon (Cinnamomum cassia)	10 (6)
Lemon (Citrus limon)	7 (4.2)
Tongkat Ali (Eurycoma longifolia)	7 (4.2)
Cloves (Syzygium aromaticum)	5 (3)
Ginseng (Panax ginseng/notoginseng/quinquefolius)	5 (3)
Dietary supplementsa
Vitamin C	134 (79.8)
Honey	75 (44.6)
Olive oil	45 (26.8)
Fish oil	39 (23.2)
Calcium	30 (17.9)
Vitamin D	19 (11.3)
Magnesium	16 (9.5)
Zinc	16 (9.5)
Vitamin E	13 (7.7)
Vitamin B	13 (7.7)
Perceived effect of HDS in enhancing body immunity
Strongly agree or agree	145 (86.3)
Unsure	23 (13.7)
Strongly disagree or disagree	0 (0)
Experienced AE from HDS use
Never	157 (93.5)
Mild AE	10 (5.9)
Moderate AE	1 (0.6)
Frequency of use
Almost everyday	101 (60.1)
A few times a week	54 (32.1)
About once a week	10 (6)
About once a month	3 (1.8)
Source of HDSb
Pharmacy	84 (50)
Online shopping platform	50 (29.8)
Health food store	36 (21.4)
Friends or family	36 (21.4)
Herbal shop	15 (8.9)
Supermarket	15 (8.9)
Grocery store	10 (6)
Source of information about HDSb
Social media or website	112 (66.7)
Family members	76 (45.2)
Friends	60 (35.7)
Pharmacist	50 (29.8)
Doctor	42 (25)
Nutritionist	30 (17.9)
Television	19 (11.3)
Radio	6 (3.6)
Consulted HCPs (doctors or pharmacists) about HDS use
Yes	88 (52.4)
No	80 (47.6)

HDS, herbal and dietary supplements; COVID-19, Coronavirus disease 2019; HCPs, healthcare providers; AE, adverse effect; SD, standard deviation.

^aOnly the top ten products/substances are presented (refer to Appendix C for the full list of HDS reported in the study).

^bRespondents can provide more than one response and therefore responses do not add up to 100 %.

3.3.2. Perceived COVID-19 prevention effects of HDS

Of all the HDS users, 86.3 % (145/168) self-reported that HDS had enhanced their body’s immunity. In terms of AEs, only a small percentage of the HDS users reported that they had experienced AEs from HDS use (6.5 %, 11/168) and these had mostly been mild (5.9 %, 10/168) (Table 3).

3.3.3. Sources of obtainment of HDS

The main source of HDS among the users was pharmacies, with half of them (50 %, 84/168) obtaining their HDS from such outlets. About one-third of the users obtained HDS from online shopping platforms (29.8 %, 50/168), while approximately one-fourth (21.4 %, 36/168) of the users obtained HDS from health food stores or their friends and family (Table 3).

3.3.4. Sources of information about HDS for COVID-19 prevention and prevalence of consultation with HCPs

When seeking information about HDS as a preventative for COVID-19, the HDS users mostly referred to social media or websites (66.7 %, 112/168), family members (45.2 %, 76/168), and friends (35.7 %, 60/168). HCPs such as pharmacists, doctors, and nutritionists were the source of information about HDS for COVID-19 prevention for less than 30 % of the HDS users (Table 3). Slightly more than half of the HDS users (52.4 %, 88/168) had consulted either pharmacists or doctors about their HDS use (Table 3).

4. Discussion

This study reports the use of HDS for COVID-19 prevention among a sample of the suburban Malaysian population. In the current study, the prevalence of using at least one HDS for COVID-19 prevention was 41.9 %. In Saudi Arabia, the reported prevalence was lower, with approximately 15 % using HDS for this purpose (Alyami et al., 2020). On the other hand, the reported prevalence was higher in Bangladesh, with 57.6 % using HDS to prevent COVID-19 (Ahmed et al., 2020).

In this study, HS were used by 18.7 % of the respondents, whereas 39.9 % used DS to prevent COVID-19. A study in Hong Kong reported a similar prevalence of HS use (19.3 %) but a lower prevalence of DS use (25.3 %) (Lam et al., 2021). In Peru, the prevalence of use of herbals for COVID-19 prevention was high, at 80 % (Villena-Tejada et al., 2021). The discrepancy between the prevalence of HDS use reported in the present study and that reported in previous studies may be attributed to the different socio-demographic profiles and local cultures of the respective study participants, as well as the times at which the surveys took place. Since the pandemic can fluctuate in terms of severity, the HDS use trends may be different at various times. Despite the studies reporting such discrepancies in the prevalence of HDS use, the existing data suggest the widespread use of HDS to prevent COVID-19.

The present study reports that individuals aged 40 and older were more likely to use HDS for COVID-19 prevention. Lam et al. (2021) reported that during the pandemic, Hong Kong residents over 55 were more likely to use traditional, complementary, and integrative medicine, including HDS. The use of HDS among the older population is not uncommon (Wahab et al., 2021). Studies conducted before the pandemic showed that older people were more likely to use HDS than their younger counterparts (Knudsen et al., 2002, Kofoed et al., 2015). Since older individuals are at higher risk of hospitalisation (Garg et al., 2020) and mortality (Ho et al., 2020) due to COVID-19, they may have a higher perceived vulnerability to the infection, which might have influenced them to practise health-promoting behaviours such as HDS use (de Zwart et al., 2010). The current study also showed that a history of pre-pandemic HDS use was an important determinant of HDS use for the prevention of COVID-19. Although not confirmed in this study, people’s familiarity and satisfaction with HDS use may influence their continued use of HDS (Ashraf et al., 2021).

In this study, the HDS used most frequently to prevent COVID-19 were garlic, ginger, black seeds, vitamin C, and honey. A study in Bangladesh also reported that ginger, black seeds and honey were commonly used (Ahmed et al., 2020). In Morocco and Peru, garlic was among the herbs most frequently used for COVID-19 prevention (El Alami et al., 2020, Villena-Tejada et al., 2021). In a survey in Saudi Arabia, almost a third of the respondents believed that consuming garlic could enhance their immunity and prevent COVID-19 (Alyami et al., 2020). The prevalent use of garlic, ginger, black seeds, and honey identified in the present study and research undertaken in other Muslim majority countries (e.g. Bangladesh, Morocco and Saudi Arabia) is unsurprising. These natural products, also known as prophetic medicine, have been used for centuries as medicine and to maintain health in Muslim cultures (Mehmood et al., 2021). Nevertheless, while scientific investigations have shown that these natural products may have the potential to prevent COVID-19 due to their antioxidant, anti-inflammatory, and antiviral activities (Rahman et al., 2021), further preclinical and clinical investigations are required to determine the effectiveness of these natural products in preventing COVID-19 (Payed et al., 2020, Rahman et al., 2022b).

The high prevalence of vitamin C use in this study (79.8 %) corroborated the findings from other studies (Ahmed et al., 2020, Alyami et al., 2020). The prevalent use of this product could be due to its wide availability in the market, good safety profile, and frequent promotion as an immune system booster (Cassa Macedo et al., 2019). Nevertheless, despite the reported potential benefits of vitamin C in enhancing immunity (Abobaker et al., 2020, Islam et al., 2021), no convincing evidence is yet available to support the use of oral supplementation of vitamin C in preventing COVID-19 among healthy individuals (Lordan et al., 2021). Nonetheless, since the intake of vitamin C is part of a healthy diet, its consumption in quantities based on the recommended dietary allowance can be recommended to maintain a healthy immune system (Zabetakis et al., 2020).

In this study, 86.3 % of the HDS users agreed that HDS had enhanced their body’s immune system, indicating high levels of satisfaction with HDS use. Additionally, most users reported that they had never experienced an AE from their HDS use. However, as described by Bahall (2017), a high level of satisfaction with HDS may overshadow or downplay the negative outcomes of HDS use. Therefore, it is common for HDS users to be less wary about suffering AEs due to HDS use or unable to attribute AEs to their use of HDS, resulting in a low reporting of AEs from HDS use.

Despite this high level of satisfaction, several safety concerns are worth highlighting. First, the authors noted that about 40 % of the HDS users in this study were also using at least one type of conventional medication. The concurrent use of HDS and conventional medications may have negative consequences due to HDS-drug interactions (e.g. altered bioavailability or efficacy, or the enhanced toxicity of conventional medications) (Asher et al., 2017). The use of multiple HDS among the users in the present study should also raise concerns about HDS-HDS interactions. In this study, the average number (± SD) of HDS used by the users was 3.9 ± 3.1 (range: 1–20), which was higher than the numbers reported in local studies conducted before the pandemic, such as those by Loo et al. (2020): 1.25 ± 0.59 (range: 1–4); and Wahab et al. (2021): 1.34 ± 0.55 (range: 1–3).

Meanwhile, social media and websites were the most common sources of information about HDS. The HDS information obtained from these sources may be inadequate in quality, commercially biased, and/or misleading (Cassa Macedo et al., 2019, Rachul et al., 2020). Additionally, it has been reported that the nutritional advice given on popular web pages about immune system booster supplements is regularly based on low-level preclinical scientific evidence (Cassa Macedo et al., 2019).

With that being said, many natural compounds have now been extensively studied for their usefulness in preventing COVID-19 (Islam et al., 2021, Payed et al., 2020). Some of the investigations of compounds with potential anti-SARS-CoV-2 effects (such as quercetin, probiotics, and zinc) rapidly progressed into clinical trials (Mrityunjaya et al., 2020). However, before more definitive evidence is available regarding the use of HDS in preventing COVID-19, it is anticipated that conflictive online information may continue to exist, presenting the public with significant challenges when they seek scientifically accurate information. In this study, the HDS users generally held the perception that there is evidence for HDS being effective in preventing COVID-19, while most non-users believed such evidence is lacking, suggesting a difference in the level of uncertainty about these products among the public.

To ensure that HDS consumers are adequately informed about HDS, especially in the context of preventing COVID-19, HCPs (especially pharmacists) should be more proactive in their consultative and information-providing roles (Rahman et al., 2022a). Additionally, pharmacists could help to prevent HDS-related problems (e.g. HDS-drug and HDS-disease interactions) by reviewing and assessing HDS use among consumers. As reported in this study, the pharmacy was reported to be the users’ most common source of HDS, which represents an opportunity for pharmacists to advise, assess, and monitor HDS use (Wahab et al., 2019a, Wahab et al., 2020). Since HDS users commonly refer to unreliable sources of information about HDS, pharmacists can provide patient education and correct misinformation during encounters with pharmacy clients seeking HDS for COVID-19 prevention.

In this study, approximately half of the HDS users had consulted HCPs about their HDS use, a higher rate than had been reported in pre-pandemic Malaysian studies (Loo et al., 2020, Mitha et al., 2013, Wahab et al., 2021, Zulkipli et al., 2018). Although the current findings suggested greater demand for HCPs’ advice about HDS during the pandemic, HCPs should be aware that the non-disclosure of HDS use remains common. Without the advice of health professionals, HDS may be used inappropriately (e.g. in excessive dosages or being used with interacting products), which may cause health problems (Kim et al., 2017). Therefore, HCPs are advised to be more proactive in initiating inquiries about HDS use during their encounters with patients.

Since the current findings showed that HDS users were more likely to be middle-aged or older individuals, HCPs should be more vigilant of HDS use among this population group. Furthermore, the prevalent use of HDS during the pandemic and the safety concerns over their use mean that increased efforts should be made to continuously provide HCPs with HDS training, education, and information, especially in the context of COVID-19.

4.1. Limitations of the study

This study has several limitations. One such limitation is the cross-sectional design, which means it only provides a snapshot of HDS use for COVID-19 prevention during the study period. Since the pandemic can fluctuate in terms of severity and extent, the trends of HDS use may differ at various times. Additionally, this study utilised an online survey that was distributed to the public mainly through social media. This may have introduced the risk of sampling bias because these platforms may have been infrequently used by certain individuals, such as older people and those in rural areas (Ting et al., 2017). Additionally, the data collected were self-reported, so the under- or over-reporting of data may have occurred. Third, since the study respondents were recruited from only one suburban town, the generalisability of the study findings is limited. Another limitation is the skewness in the distribution of the respondents, based on their socio-demographic characteristics (e.g. gender, ethnicity, and educational level), which resulted in limited representativeness of the Malaysian population and thus further limited the generalisability of the results.

Despite these limitations, the present study provides insights into HDS use for COVID-19 prevention that could enhance the understanding and awareness among key stakeholders such as the Malaysian health authorities, health professional bodies, healthcare providers, and researchers. Since COVID-19 continues to spread despite the high vaccination rate and given the country’s endemic status, the use of HDS as a preventative for COVID-19 could remain prevalent. Future studies should be conducted among a larger sample of the general public and across multiple geographical areas to better understand the use of HDS during the endemic phase of COVID-19.

5. Conclusion

The use of HDS to prevent COVID-19 was found to be common among a sample of the general public of a suburban town in Malaysia. Although HDS use appeared to be safe and highly satisfactory for the users, several safety concerns were raised, such as the concurrent use of HDS with conventional medications, the use of unreliable sources of information, and a lack of consultation with HCPs regarding HDS use. Due to the widespread use of HDS during the pandemic, HCPs (especially pharmacists) should be more proactive in assessing the appropriateness of HDS use among consumers and providing them with education about HDS, which could ensure the safe use of HDS.

CRediT authorship contribution statement

Mohd Shahezwan Abd Wahab: Conceptualization, Data curation, Formal analysis, Methodology, Writing – original draft, Writing – review & editing. Humaira’ Hamdi: Conceptualization, Data curation, Methodology. Mahmathi Karuppannan: Supervision, Writing – review & editing. Aida Azlina Ali: Formal analysis, Methodology. Muhammad Harith Zulkifli: Writing – original draft. Sandra Maniam: Writing – original draft, Writing – review & editing. Carolina Oi Lam Ung: Supervision, Writing – review & editing.

Declaration of Competing Interest

The authors declare that they have no competing interests.

Appendix A. Supplementary material

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