Abstract
Background
Dietary supplement and over-the-counter product use is common among people with a history of cancer and may raise safety concerns, including treatment interactions. We assessed the frequency, patterns, temporal variation and correlates of dietary supplement and over-the-counter product use among adults with a self-reported history of cancer in Poland.
Patients and methods
We performed a repeated cross-sectional analysis of six annual waves (2020–2025) of a nationwide quota-based web survey in Poland. Among 1,271,102 respondents overall, 79,588 reported a history of cancer. Dietary supplement and over-the-counter product use in the previous 12 months was assessed by frequency and reported product category or purpose of use. Correlates of any dietary supplement and over-the-counter product use were examined using multivariable logistic regression.
Results
Any dietary supplement and over-the-counter product use was reported by 61.8% of respondents, including daily use in 26.9%, whereas 38.2% reported no use. The most frequently selected categories were multivitamins, digestive products, hair/skin products and sleep products. Men and older respondents had lower odds of dietary supplement and over-the-counter product use, whereas higher education and coexisting non-cancer comorbidities were associated with greater odds of use.
Conclusions
Dietary supplement and over-the-counter product use was frequently reported among respondents and showed distinct sociodemographic and health-related patterns. Including these products in routine medication histories may help identify potential interactions and other clinically relevant issues.
Supplementary information
The online version contains supplementary material available at https://doi.org/10.1007/s00520-026-11263-z.
Keywords: Dietary supplements, Over-the-counter products, History of cancer, Supportive care, Poland
Introduction
Cancer survivorship has become a major component of oncology, with steadily growing numbers of adults living for years after a cancer diagnosis and treatment. Nutritional status, body weight and lifestyle behaviours are recognized as important determinants of long-term health and quality of life in this population. Current survivorship guidance emphasizes a healthy dietary pattern and regular physical activity and does not recommend routine supplement use for most cancer survivors [1, 2]. Despite these recommendations, dietary supplement use after cancer diagnosis is very common: US data indicate that most adult survivors use vitamin or mineral supplements, with about 70% reporting any supplement and almost half reporting multivitamin–mineral products [3, 4]. Large cohort and registry studies from Europe and Asia similarly describe frequent use among survivors of breast, colorectal and other cancers, with prevalence often exceeding that in the general population [5–7].
Patterns of use are heterogeneous. Survivors most frequently report multivitamin products, single-nutrient supplements such as vitamin D, calcium or antioxidants and products marketed for fatigue, immune support or joint health [8–10]. Motivations include hopes of preventing recurrence, strengthening the immune system, reducing treatment toxicity and gaining a sense of control over health; many users perceive supplements as intrinsically safe or “natural” [11–14]. However, disclosure to treating oncologists is inconsistent and supplement use is more common among women, older survivors, those with higher education or income and individuals with multiple comorbidities or higher symptom burden [3, 5, 8, 15].
Evidence on clinical benefits and harms of supplements in oncology remains uncertain and sometimes conflicting. The lack of robust trial data supporting routine supplementation for cancer control or survival and caution against high-dose antioxidant or phytochemical preparations during active treatment are highlighted [11, 12]. Data show that the use of certain antioxidant supplements before and during treatment was associated with worse invasive disease-free and overall survival, raising concern about interference with cytotoxic mechanisms [16]. Alongside concerns about direct effects on tumour biology or treatment efficacy, herb–drug and supplement–drug interactions have been documented, particularly with products affecting cytochrome P450 or transport proteins, underscoring the need for careful medication review in oncology practice [17, 18].
Most existing studies on supplement use in oncology rely on clinic-based samples, disease-specific cohorts or volunteer panels, often with modest sample sizes and limited information on social position, healthcare access and financial barriers [4, 6, 7, 10, 13, 15]. Large, multi-wave data on dietary supplement and over-the-counter product use among people with a history of cancer in Poland remain limited. Previous Polish research addressed complementary and alternative medicine more broadly, whereas the present study focuses specifically on jointly assessed dietary supplements and over-the-counter products [19].
This study aimed to evaluate the proportion and frequency of dietary supplement and over-the-counter product use among adults with a self-reported history of cancer, and to identify sociodemographic, health-related, behavioural and healthcare access correlates of use and their temporal patterns across six consecutive annual waves of a large nationwide online health survey in Poland.
Materials and methods
Study design and data source
This cross-sectional study pooled six annual waves (2020–2025) of a nationwide, quota-based web survey of adults in Poland, the “National Health Test”, conducted by Medonet, a health-oriented internet platform (1,271,102 total responses). Data were collected using computer-assisted web interviewing (CAWI). Participation was voluntary and anonymous. Respondents were recruited via a large health-oriented internet platform and partner media, with additional outreach aimed at broad coverage across age and educational groups. For each annual wave, quota targets were applied for sex, age, education, place of residence and region to approximate the demographic structure of the adult population. Quota targets were used to improve demographic coverage of the overall survey sample; however, recruitment was non-probability-based and the quotas do not establish representativeness of the subgroup with a self-reported history of cancer. Because no stable personal identifiers were collected and records were not linkable across years, each questionnaire was treated as an independent observation (repeated cross-sectional design). This study followed the Strengthening the Reporting of Observational Studies in Epidemiology statement [20].
Study population
The analytic cohort included respondents aged 18 years or older who reported residence in Poland and self-reported a history of cancer (n = 79,588). Cancer history was derived from the survey item on physician-diagnosed chronic diseases that included cancer as a response option. Observations with missing data for a given analysis were excluded from that analysis (complete-case approach at the analysis level).
Study variables
The exposure of interest was the combined self-reported use of dietary supplements and preparations available without prescription during the preceding 12 months. These two categories were assessed jointly in the questionnaire and could not be distinguished in the present analysis. Frequency of use was recorded using eight response categories: every day; several times a week; once a week; several times a month; once a month; less than once a month; only for a limited period; and no use in the preceding 12 months. For regression analyses, this variable was dichotomized as any use versus no use, with any use comprising all categories other than no use.
Respondents who reported any use were subsequently asked a multiple response question regarding both the type of preparation used and its intended purpose. The response options therefore included both product categories and purposes of use and were not mutually exclusive. Each response category was coded as a separate binary indicator and summarized among respondents reporting any use. These data are described as “reported product categories or purposes of use”; the term “motivations” is not used because motivations were not directly assessed. The exact original Polish wording of both survey items and all response options, together with an English translation, is provided in Supplementary Table S1.
Candidate correlates of any use were prespecified from survey domains covering sociodemographic characteristics, self-rated health, comorbidities, healthcare utilization and access, financial barriers to care, transport-related access to medical appointments and frequency of stressful situations.
Statistical analysis
Categorical variables were summarized as counts and percentages. Age was summarized as mean with standard deviation. Between-wave differences across survey years were evaluated using chi-square tests for categorical variables and parametric or nonparametric tests for continuous variables depending on distributional assumptions. To identify correlates of any dietary supplement and over-the-counter product use (any use versus never), univariable logistic regression models were first fitted for each candidate predictor. Predictors were entered into the multivariable logistic regression model if the corresponding univariable analysis yielded p < 0.30. For categorical predictors with more than two levels, this criterion was considered met if at least one non-reference category had p < 0.30; once selected, the entire predictor, including all categories, was retained in the multivariable model. Effect estimates were reported as adjusted odds ratios (aORs) with 95% confidence intervals (CIs). Age was modeled as a continuous variable (per 1-year increase) and categorical predictors were included using indicator coding with prespecified reference categories. All tests were two-sided, with p < 0.05 considered statistically significant. All analyses were performed using R (version 4.5.1).
Ethical considerations
This study was a secondary analysis of de-identified survey data. Participation in the survey was anonymous and voluntary; respondents were informed about the survey purpose and data use and provided electronic consent before proceeding. The study was conducted in accordance with applicable data protection regulations and the principles of the Declaration of Helsinki. The study protocol was approved by the Ethics Committee of Jagiellonian University Medical College (No. 118.0043.1.495.2025; December 11, 2025).
Results
Participant characteristics
The analysis included 79,588 adults with a self-reported history of cancer, of whom 49,649 (62.4%) were women. The mean (SD) age was 62.05 (12.68) years. Most respondents had secondary education (35,381; 44.5%) or a master’s degree (28,197; 35.4%); 7830 (9.8%) reported vocational education. Residence was distributed across rural areas (15,197; 19.1%) and urban settings, including towns over 500 thousand inhabitants (14,355; 18.0%). Most respondents were married (48,132; 60.5%); 10,126 (12.7%) were single, 10,048 (12.6%) reported an informal relationship and 9396 (11.8%) were widowed. Retired or disabled respondents constituted 46,773 (58.8%), while 26,420 (33.2%) were employed under an employment contract or self-employed. Comorbidities other than cancer were reported by 67,861 respondents (85.3%). Self-rated physical health was most commonly reported as average (34,999; 44.0%) or good (26,670; 33.5%), whereas self-rated mental health was most commonly reported as good (35,038; 44.0%) or very good (16,459; 20.7%).
Reported use, frequency and reported product categories
Dietary supplement and over-the-counter product use within the preceding 12 months was reported by 49,165 respondents (61.8%); daily use was reported by 21,446 respondents (26.9%). Among users, the most frequently selected category was multivitamin preparations (25,827; 52.5%) (Table 1).
Table 1.
Patterns of dietary supplement and over-the-counter product use among adults with a self-reported history of cancer, Poland, 2020–2025
| Measure | No. (%) |
|---|---|
| Frequency of use in the prior 12 months (n = 79,588) | |
| Never | 30,423 (38.2) |
| Only for a limited time | 8937 (11.2) |
| Less than once a month | 2465 (3.1) |
| Once a month | 939 (1.2) |
| Several times a month | 3767 (4.7) |
| Once a week | 1483 (1.9) |
| Several times a week | 10,128 (12.7) |
| Every day | 21,446 (26.9) |
| Reported product categories or purposes of use (n = 49,165)a | |
| Multivitamin preparations (prophylactic use, fatigue, infection) | 25,827 (52.5) |
| Preparations to improve digestion or reduce symptoms such as constipation, flatulence or heartburn | 13,379 (27.2) |
| Preparations to improve hair and skin condition | 10,467 (21.3) |
| Preparations to facilitate falling asleep | 7765 (15.8) |
| Preparations to improve memory and concentration | 6004 (12.2) |
| Preparations to improve eyesight and visual comfort | 5449 (11.1) |
| Preparations to improve mood and well-being | 3907 (7.9) |
| Preparations to support weight loss | 3576 (7.3) |
| Preparations to improve potency | 952 (1.9) |
| Other preparations or other purposes | 7812 (15.9) |
aMultiple response item administered only to respondents who reported any dietary supplement/over-the-counter use; categories are not mutually exclusive. Abbreviations: n number of respondents
Temporal patterns across survey waves (2020–2025)
Across survey waves, dietary supplement and over-the-counter product use differed significantly (p < 0.001), with the highest proportion of any use observed in 2021 and the lowest in 2025. Daily use also varied between waves, ranging from 23.6% in 2020 to 30.2% in 2021 and 26.2% in 2025. These between-wave differences are shown in Fig. 1.
Fig. 1.
Temporal variations in dietary supplement and over-the-counter product use in Poland, 2020–2025
Correlates of any dietary supplement and over-the-counter product use
Univariable associations are presented in Supplementary Table S2. In the multivariable model, dietary supplement and over-the-counter product use was associated with several sociodemographic, health-related and psychosocial characteristics (Table 2). Higher educational attainment showed the strongest positive association, with the highest odds among respondents with university-level education. More frequent stressful situations were also associated with higher odds of use, whereas male sex and older age were associated with lower odds. Associations with the remaining sociodemographic, health-related and healthcare access variables were generally smaller or heterogeneous. Dietary supplement and over-the-counter product use was associated with self-rated mental health, although the adjusted estimates did not increase consistently across progressively poorer categories.
Table 2.
Factors associated with any use of dietary supplements and over-the-counter products among adults with a self-reported history of cancer
| Variable | Category | N | n | Multivariable aOR (95% CI) | p |
|---|---|---|---|---|---|
| Sex | Female | 49,649 | 32,893 | 1 | ref |
| Male | 29,939 | 16,272 | 0.675 (0.654–0.698) | < 0.001 | |
| Age | Per 1-year increase | - | - | 0.994 (0.992–0.996) | < 0.001 |
| Education | Primary | 1903 | 919 | 1 | ref |
| Vocational | 7830 | 3843 | 1.128 (1.018–1.250) | 0.021 | |
| Secondary | 35,381 | 20,997 | 1.637 (1.489–1.800) | < 0.001 | |
| Bachelor | 6277 | 4030 | 2.117 (1.902–2.356) | < 0.001 | |
| MSc | 28,197 | 19,376 | 2.444 (2.218–2.693) | < 0.001 | |
| Place of residence | Rural area | 15,197 | 9211 | 1 | ref |
| Town up to 19,000 inhabitants | 9715 | 6032 | 1.094 (1.036–1.155) | 0.001 | |
| Town 20,000–49,000 inhabitants | 12,713 | 7799 | 1.066 (1.014–1.121) | 0.012 | |
| Town 50,000–99,000 inhabitants | 9536 | 5953 | 1.100 (1.041–1.161) | 0.001 | |
| Town 100,000–199,000 inhabitants | 8840 | 5483 | 1.085 (1.026–1.148) | 0.004 | |
| Town 200,000–499,000 inhabitants | 9232 | 5770 | 1.077 (1.019–1.139) | 0.008 | |
| City over 500,000 inhabitants | 14,355 | 8917 | 1.042 (0.992–1.094) | 0.102 | |
| Marital status | Single | 10,126 | 6654 | 1 | ref |
| Married | 48,132 | 29,240 | 0.937 (0.894–0.983) | 0.007 | |
| Informal relationship | 10,048 | 6426 | 1.004 (0.946–1.066) | 0.898 | |
| Widowed | 9396 | 5638 | 0.935 (0.879–0.994) | 0.032 | |
| Other | 1886 | 1207 | 0.991 (0.892–1.101) | 0.870 | |
| Professional status | Employed under an employment contract or self-employed | 26,420 | 17,790 | 1 | ref |
| Employed under another contract | 2473 | 1583 | 0.970 (0.888–1.060) | 0.503 | |
| Running a farm | 626 | 377 | 0.947 (0.801–1.119) | 0.520 | |
| Unemployed with entitlement to benefits | 655 | 385 | 0.823 (0.700–0.969) | 0.019 | |
| Unemployed without entitlement to benefits | 2066 | 1263 | 0.858 (0.779–0.945) | 0.002 | |
| Retired or disabled | 46,773 | 27,395 | 0.925 (0.884–0.967) | 0.001 | |
| Not working/student | 575 | 372 | 0.866 (0.724–1.035) | 0.114 | |
| Self-assessment of physical health | Very good | 5740 | 3418 | 1 | ref |
| Good | 26,670 | 16,152 | 0.931 (0.874–0.990) | 0.023 | |
| Average | 34,999 | 21,975 | 0.916 (0.858–0.977) | 0.008 | |
| Poor | 10,790 | 6781 | 0.867 (0.804–0.936) | < 0.001 | |
| Very poor | 1389 | 839 | 0.802 (0.704–0.915) | 0.001 | |
| Self-assessment of mental health | Very good | 16,459 | 9259 | 1 | ref |
| Good | 35,038 | 21,352 | 1.163 (1.117–1.212) | < 0.001 | |
| Average | 21,077 | 13,833 | 1.283 (1.222–1.347) | < 0.001 | |
| Poor | 6211 | 4203 | 1.275 (1.188–1.368) | < 0.001 | |
| Very poor | 803 | 518 | 1.191 (1.015–1.397) | 0.032 | |
| Chronic health problems | No | 13,514 | 7981 | 1 | ref |
| Yes | 66,074 | 41,184 | 1.108 (1.061–1.156) | < 0.001 | |
| Chronic diseases other than cancer | No comorbidities | 11,727 | 7120 | 1 | ref |
| Comorbidities present | 67,861 | 42,045 | 1.103 (1.055–1.153) | < 0.001 | |
| Cancer in the family | No | 18,664 | 11,222 | 1 | ref |
| I do not know | 6313 | 3730 | 1.031 (0.971–1.095) | 0.318 | |
| Yes | 54,611 | 34,213 | 1.030 (0.995–1.067) | 0.098 | |
| Last visit to a primary care physician | Less than 6 months ago | 58,033 | 35,877 | 1 | ref |
| 6–12 months ago | 11,264 | 7029 | 1.010 (0.966–1.056) | 0.656 | |
| More than 1 year ago | 7618 | 4723 | 1.010 (0.957–1.066) | 0.723 | |
| I do not remember/long time ago | 2472 | 1416 | 0.860 (0.787–0.940) | 0.001 | |
| Never | 201 | 120 | 0.879 (0.658–1.174) | 0.381 | |
| Last visit to a specialist | Less than 6 months ago | 61,958 | 38,663 | 1 | ref |
| 6–12 months ago | 9902 | 6113 | 0.978 (0.933–1.024) | 0.339 | |
| More than 1 year ago | 5789 | 3396 | 0.882 (0.831–0.937) | < 0.001 | |
| I do not remember/long time ago | 1769 | 907 | 0.690 (0.623–0.764) | < 0.001 | |
| Never | 170 | 86 | 0.811 (0.595–1.107) | 0.187 | |
| Ever skipped a doctor's appointment for financial reasons | No | 38,540 | 23,621 | 1 | ref |
| Yes | 17,271 | 11,321 | 1.038 (0.986–1.093) | 0.159 | |
| I have never been in such a situation | 23,777 | 14,223 | 0.950 (0.900–1.001) | 0.056 | |
| Ever skipped a dentist appointment for financial reasons | No | 37,947 | 23,309 | 1 | ref |
| Yes | 19,015 | 12,398 | 0.995 (0.949–1.044) | 0.853 | |
| I have never been in such a situation | 22,626 | 13,458 | 0.946 (0.898–0.996) | 0.036 | |
| Ever skipped buying a prescription drug for financial reasons | No | 43,236 | 26,708 | 1 | ref |
| Yes | 12,541 | 7980 | 0.950 (0.901–1.003) | 0.062 | |
| I have never been in such a situation | 23,811 | 14,477 | 1.056 (1.003–1.112) | 0.038 | |
| Ever foregone the purchase of necessary medical equipment for financial reasons | No | 33,061 | 20,246 | 1 | ref |
| Yes | 10,869 | 7170 | 1.089 (1.028–1.154) | 0.004 | |
| I have never been in such a situation | 35,658 | 21,749 | 0.998 (0.959–1.039) | 0.927 | |
| Ability to arrange transportation to a doctor's appointment | Yes, without any difficulty | 58,319 | 35,552 | 1 | ref |
| Yes, but with some difficulty | 10,781 | 7261 | 1.198 (1.144–1.256) | < 0.001 | |
| Yes, but with great difficulty | 2290 | 1461 | 1.057 (0.964–1.158) | 0.242 | |
| I am unable to arrange transportation to my medical appointments | 1225 | 727 | 0.919 (0.814–1.038) | 0.173 | |
| I do not need transportation to my medical appointments—I walk there | 4890 | 2924 | 0.989 (0.929–1.053) | 0.736 | |
| It is hard to say | 2083 | 1240 | 0.891 (0.813–0.978) | 0.015 | |
| Frequency of experiencing stressful situations | Never | 2444 | 1023 | 1 | ref |
| Less than once a month | 16,107 | 8502 | 1.272 (1.165–1.389) | < 0.001 | |
| Once a month | 5121 | 3033 | 1.531 (1.385–1.693) | < 0.001 | |
| Several times a month | 17,083 | 10,665 | 1.627 (1.488–1.779) | < 0.001 | |
| Once a week | 5094 | 3257 | 1.714 (1.548–1.898) | < 0.001 | |
| Several times a week | 19,530 | 13,132 | 1.826 (1.668–2.000) | < 0.001 | |
| Every day | 14,209 | 9553 | 1.710 (1.555–1.880) | < 0.001 |
Abbreviations: aOR adjusted odds ratio, CI confidence interval, N group size, n number of respondents reporting any dietary supplement and over-the-counter product use. For categorical predictors with more than two levels, the predictor was retained for multivariable modelling if at least one non-reference category had p < 0.30 in the corresponding univariable analysis; once selected, all categories of that predictor were included in the model. Statistical significance was defined as p < 0.05
Healthcare access variables showed heterogeneous associations after adjustment. A longer interval since the last specialist visit was associated with lower odds of dietary supplement and over-the-counter product use, whereas foregoing necessary medical equipment for financial reasons and reporting some difficulty arranging transportation to medical appointments were associated with higher odds. Other healthcare access and financial barrier indicators did not show consistent independent associations.
Discussion
In this repeated cross-sectional survey of Polish adults with a self-reported history of cancer, dietary supplement and over-the-counter product use was frequently reported, including daily use in a substantial proportion of respondents. These findings support considering non-prescription products as part of routine medication history in cancer care and follow-up. The proportion reporting use was broadly comparable with estimates from survivorship cohorts in other countries [3, 6, 10], although the non-probability survey design does not support direct population-level prevalence estimates. Use varied across survey waves, with the highest proportion in 2021 and the lowest in 2025, without a consistent year-to-year decline. Because the study period encompassed both the COVID-19 pandemic and subsequent years, changes in health-related behaviours, healthcare circumstances and the composition of respondents to the voluntary online survey may have contributed to this between-wave variation.
The strongest correlates point to dietary supplement and over-the-counter product use as a behaviour patterned by sociodemographic factors and health perceptions. Higher education and female sex were associated with greater use, consistent with multiple survivorship studies describing higher uptake among women and individuals with higher socioeconomic position [8, 10, 21]. Dietary supplement and over-the-counter product use was associated with self-rated mental health, although the adjusted estimates did not show a monotonic gradient across progressively poorer categories. Previous studies have proposed that supplement use may relate to coping, reassurance or perceived control [13–15]. However, these mechanisms were not directly assessed in the present survey and should be regarded as hypotheses rather than explanations of the observed association.
The positive association between comorbidities and dietary supplement and over-the-counter product use is clinically consequential because interaction risk increases with the number of concomitant agents and because many dietary supplements are taken chronically without systematic review. Incomplete disclosure of complementary and non-prescription product use provides a practical rationale for proactive questioning in oncology care. Huemer et al. reported that only 42.2% of CAM users had discussed their use with an oncologist, while in a Polish study 46.6% of CAM users had not informed their physician [19, 22]. Clinical practice recommendations by Balneaves et al. emphasize that oncology healthcare professionals should routinely discuss CAM use, assess the products and therapies being used and document relevant details as part of ongoing care [23]. Although these studies and recommendations address CAM more broadly, they support systematic inquiry about dietary supplements and other non-prescription products that may otherwise be omitted from the medication history. Pharmacokinetic interactions are particularly relevant because herbs, food and dietary supplements may alter CYP-mediated metabolism of anticancer treatments. Gougis et al. reviewed potential interactions involving major cytochrome P450 isoforms relevant to anticancer drug metabolism, including CYP3A4, CYP2D6, CYP1A2 and CYP2C8 [24]. Potential herb–drug interactions involving additional mechanisms, including drug transport pathways, have also been reported [17, 18].
Current survivorship guidance emphasizes a healthy dietary pattern and regular physical activity and does not recommend routine supplement use for most cancer survivors; supplementation may be appropriate in selected circumstances based on individual nutritional or clinical needs [1, 2]. Evidence syntheses and educational reviews underscore uncertainty of benefit and highlight potential harms, particularly with high-dose antioxidants or biologically active preparations during active treatment [11, 12]. In the MARIE cohort, concurrent antioxidant supplementation during chemotherapy or radiotherapy was associated with higher all-cause mortality and poorer recurrence-free survival [25]. In a prospective observational ancillary study conducted within the randomized SWOG S0221 trial, antioxidant use before and during chemotherapy yielded point estimates suggesting higher hazards of recurrence and death; however, the corresponding confidence intervals included unity [16]. Together, these observational findings raise a potential safety concern but do not establish a causal effect of antioxidant supplementation on cancer outcomes. For clinicians, a pragmatic counselling approach is to (1) elicit a complete list of dietary supplements and over-the-counter products, including dose and brand when possible, (2) clarify the intended purpose and expected benefit, (3) screen for potential interactions and duplication with prescribed therapy, and (4) advise caution with high-dose antioxidant supplements during chemotherapy or radiotherapy unless there is a clear medical indication, while prioritizing correction of confirmed deficiencies and dietitian-supported strategies [1, 25].
Healthcare access variables showed heterogeneous associations after adjustment. Compared with respondents who had seen a specialist within the previous 6 months, those reporting a specialist visit more than 1 year earlier or not remembering the timing of their last specialist visit had lower odds of dietary supplement and over-the-counter product use. In contrast, foregoing necessary medical equipment for financial reasons and reporting some difficulty arranging transportation to medical appointments were associated with higher odds of use. Other indicators of financial barriers or transportation difficulties did not show consistent independent associations. Given the cross-sectional design and the heterogeneity of these findings, no common behavioural mechanism should be inferred.
These findings support routinely asking about dietary supplements and over-the-counter products as part of medication review. Because non-prescription products may be incompletely disclosed and may contribute to pharmacokinetic interactions or complicate adverse effect attribution, clinicians should document the products used, assess their intended purpose and potential interactions and provide evidence-based counselling where appropriate.
Study limitations
This open, web-based survey of adult internet users in Poland applied quota control but not probability sampling; individuals with limited internet access or digital skills, very advanced disease or severe functional impairment are likely underrepresented. The proportions observed among respondents should therefore not be interpreted as population prevalence or extrapolated to all people with a history of cancer in Poland. All measures were self-reported, with cancer captured by a single checklist item and no data on tumour site, histology, stage, time since diagnosis, current status or type and line of oncologic treatment. Dietary supplements and preparations available without prescription were assessed jointly in a single survey item and cannot be separated in the present analysis. The survey used broad 12-month frequency categories and did not collect information on product composition, dose, duration or source of recommendation. The follow-up multiple response item combined product categories and intended purposes and did not directly assess broader behavioural or psychological motivations. The cross-sectional design and six repeated cross-sections without individual linkage preclude temporality, causality and within-person trajectories. Residual confounding is likely because income, wealth, detailed occupational status, treatment regimen, physician counselling and beliefs about complementary and alternative medicine were unavailable or coarsely measured. In addition, limited information on non-response and partially completed questionnaires further restricts external validity.
Conclusions
Dietary supplement and over-the-counter product use was frequently reported among respondents with a self-reported history of cancer and was associated with selected sociodemographic and health-related characteristics. Including these products in routine medication histories may help identify potential interactions and other clinically relevant issues.
Supplementary information
Below is the link to the electronic supplementary material.
(DOCX 35.8 KB)
Author contributions
A.Z.-Z. and M.P. initiated and designed the study. A.Z.-Z. organized data access. A.Z.-Z. and M.P. prepared the first manuscript draft. I.K.-B. supported methodological planning, was responsible for ethical approval and critically revised the text with a focus on public health implications. A.Z.-Z., M.P. and R.P.-M. contributed to the evidence review. R.P.-M. interpreted the results from a clinical perspective and participated in substantive manuscript revision. M.P. led scientific and clinical oversight. All authors reviewed and approved the final manuscript and accept responsibility for the integrity of the work.
Funding
The authors confirm that this study, including manuscript preparation and the decision to submit for publication, was conducted without any financial support, grants, or other external funding. No other conflicts of interest are declared for this study.
Data availability
The data analyzed in this study are available from the corresponding author upon reasonable request.
Declarations
Conflict of interest
The authors declare no competing interests.
Footnotes
Publisher’s Note
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Contributor Information
Anna Zimny-Zając, Email: anna.zimny.zajac@uj.edu.pl.
Mirosława Püsküllüoğlu, Email: miroslawa.puskulluoglu@krakow.nio.gov.pl.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
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Data Availability Statement
The data analyzed in this study are available from the corresponding author upon reasonable request.