The demand for health in a time of uncertainty – insights from dietary supplement demand during the COVID-19 pandemic

Over the years, dietary supplements have become popular as individuals increasingly seek healthier lifestyle options, alongside increased advertising of these products (Blendon et al., 2001; Burdock et al., 2006; Royne et al., 2014). Research suggests that because of the novel nature of the coronavirus disease (COVID-19) pandemic and its negative consequences, people had to make various lifestyle adjustments, including the use of masks, social distancing, and making some healthy consumption choices such as the use of dietary supplements (Lordan et al., 2021; Michienzi and Badowski, 2020; Speakman et al., 2021). Some reports from the early days of the pandemic indicate that over that period, sales of dietary supplements increased substantially (Grebow, 2020). Several factors may have influenced the widespread use of dietary supplements during the pandemic. The most notable of these factors are the deleterious nature of the coronavirus, uncertainties surrounding the production and supply of vaccines, and the belief that dietary supplements can strengthen the immune system (NIH, 2021). In this paper, I examine the demand for dietary supplements during the COVID-19 period and compare it to demand before the onset of the pandemic.

I consider two main reasons for studying the impact of the COVID-19 pandemic on the demand for dietary supplements. First, while dietary supplements are primarily supposed to supplement one's diet, many people use them for sickness prevention or treatment, even though they are not supposed to be used in that way (Blendon et al., 2001; Dickinson et al., 2014; Garthe and Maughan, 2018). Therefore, the use of dietary supplements during the pandemic for protection against the coronavirus suggests some form of risky health behavior. This trend is particularly concerning, as there was no conclusive evidence demonstrating that dietary supplements were effective in combating COVID-19 (NIH, 2021).

Second, while some reports suggest an increase in demand for dietary supplements during the pandemic (Grebow, 2020), little empirical research exists in this area. Dietary supplements come in various forms; however, multivitamin, multimineral, vitamin, and mineral supplements are the most widely used types of dietary supplements among U.S. households (Bailey, 2020; Kantor et al., 2016). Vitamin and mineral supplements are widely believed to be beneficial for health, particularly in preventing chronic diseases and boosting immune function (Michienzi and Badowski, 2020). Protein supplements are popular among athletes and active individuals seeking muscle growth and performance enhancement (Garthe and Maughan, 2018; Maughan, 2013; Maughan et al., 2018; Pasiakos et al., 2015). It is plausible that the pandemic may have increased the demand for some types of dietary supplements; however, this increase may not apply to all types of dietary supplements, especially those that are not typically marketed as boosting immune function. Additionally, it is also possible that, while demand for dietary supplements may have increased significantly in the initial periods following the onset of the pandemic, these effects were not long-lasting.

Against this background, this paper uses weekly store-level sales data on dietary supplements from January 2019 to December 2020 from NielsenIQ Retail Scanner Data (NRSD) to estimate the extent to which the COVID-19 pandemic impacted the demand for different types of dietary supplements. The outcome of interest is sales of the various dietary supplement types defined by NielsenIQ. The study uses a panel fixed-effects approach that compares sales of dietary supplements before and during the COVID-19 period. I first compare demand between the pre-COVID-19 period and the actual COVID-19 period. I then explore differences in demand across the individual weeks that preceded the onset of the COVID-19 pandemic and the weeks following the onset of the COVID-19 pandemic.

This study's primary contribution is to provide a thorough empirical analysis of how the COVID-19 pandemic impacted the demand for dietary supplements in the U.S. Little empirical work exists in that regard. To that effect, this study makes three specific contributions to the literature on dietary supplement demand. First, to my knowledge, this study provides the first comprehensive empirical estimates of the impact of the COVID-19 pandemic on dietary supplement demand, which I measure via sales. By using scanner data, I can assess how sales across various categories of dietary supplements differed before and during the pandemic as compared to studies that use survey data collected after the onset of the pandemic to assess how different socio-economic factors impacted the use of dietary supplements (Austin et al., 2023; Jackson et al., 2025; Raffoul et al., 2023; Turner et al., 2024). Using scanner data also enables examining temporal variations in the effects of the COVID-19 pandemic on the demand for dietary supplements, offering insights into both the immediate and long-term responses to the onset of the pandemic using an event study approach. Lastly, this study contributes to the limited research on the demand for dietary supplements. Few studies provide empirical estimates of the demand for dietary supplements in the U.S. (Austin et al., 2017, 2018). This study contributes to this literature by providing some insights into the demand for dietary supplements using more recent data.

The results show that over the COVID-19 period, there was a notable increase in sales of dietary supplements across most of the product modules. These effects were mainly driven by increased sales of dietary supplements in March 2020. While the findings mostly indicate positive and statistically significant effects of the COVID-19 pandemic, the findings also indicate that in most cases, sales began to decline around the end of March 2020. The results also indicate that overall, there is an increasing trend in dietary supplement sales beyond the impact of the COVID-19 pandemic.

This study has important policy implications, especially considering the growing demand for dietary supplements as well as the less stringent regulations that guide their sale. The findings highlight the potential need for better regulation around the marketing and sale of dietary supplements, given that the COVID-19 pandemic has shown how much value people place on dietary supplements.

All the data used in this study comes from the NielsenIQ Retail Scanner Data (NRSD). The NRSD currently has over 45,000 participating retail stores across the U.S., providing data on a wide range of products across multiple product categories, including food and non-food items. The data includes average price and weekly volume at the Universal Product Code (UPC) level. The paper used two years of retail scanner data covering the years 2019 and 2020.

Based on the hierarchy of product classifications provided by NielsenIQ, dietary supplements are captured within the product group identified as “vitamins”. It is important to note that, while the product group is labeled as vitamins, the products that fall under this classification comprise more than just vitamin supplements. This is evident in the product classification hierarchy below the product group, which further disaggregates these products into nine product modules. These nine modules are (1) nutritional supplements; (2) complete nutritional products; (3) tonics; (4) multiple; (5) vitamin B complex with vitamin C; (6) children flavored chewable; (7) remaining; (8) minerals; and (9) protein supplements.

It is important to note that while the classification of dietary supplements between the NielsenIQ data and other descriptions provided in the previous section appears to be fairly similar, there are some notable discrepancies. The “nutritional supplements” module includes a wide range of products, comprising mainly dietary, oil, and herbal supplements. Several other products are also found in this module; however, dietary, oil, and herbal supplements constitute over 90% of the products found in this module. There are a few instances where vitamin, mineral, and protein supplements also appear in this module. These discrepancies found in the classification of products into the module suggest that there is no strict naming convention used by producers to market these products, even more so because dietary supplements collectively represent the term formally recognized under U.S. regulations (Burdock et al., 2006). The “complete nutritional products” module consists of food products mostly in the form of beverages that are marketed as providing nutritional benefits. The other product modules appear to be mostly grouped based on their nutrient components. The “multiple” module consists of multivitamins and combinations of minerals. The module “Vitamin B complex with Vitamin C” represents a combination of B vitamins and Vitamin C, while “remaining” includes all other vitamins, such as vitamins A, C, D, E, K, and some Vitamin B. The “minerals” module includes supplements that provide nutrients such as calcium, iron, magnesium, selenium, and zinc.

For convenience, the study categorizes sales based on the same product modules as provided by NielsenIQ. To create weekly sales, I aggregate sales data to the store-week level for all dietary supplement product modules and then carry out two data restrictions. First, only stores that appear in both 2019 and 2020 are included. Second, stores that do not record any dietary supplement sales over the entire sample period are excluded. This results in a panel of stores that appear over the 104 weeks considered for the study.

To explore the impact of the COVID-19 pandemic on the demand for supplements, the study used a panel fixed effects approach for the analysis. I use two variants of a two-way fixed effects model. The main model estimates the aggregate effect of the COVID-19 period, starting from the first week of March 2020, on the sale of dietary supplements. I use a Poisson Pseudo Maximum Likelihood (PPML) approach following Silva and Tenreyro (2006) to estimate the effects of the pandemic on dietary supplement sales. Given the excess zeros in the sales data, I deem this the most tractable approach. I use the PPML approach rather than the logarithm of sales because of its ability to handle zero sales associated with some stores in some weeks. Furthermore, the coefficients can be easily interpreted as semi-elasticities in this case, making it more appealing. This regression is specified as:

$Yiwt$ represents sales for a dietary supplement category in store $i$ in week $w$⁠, and year $t$⁠. $Covid$ is a binary indicator equal to 1 for the first week of March 2020 and the weeks after, and 0 for the weeks preceding March 2020. $αi$, $αw$, and $αt$ are store, week, and year fixed effects, respectively. $εiwt$ is the error term.

I estimate a second model where I modify Equation (1), and instead of a grouped single effect for the COVID-19 period, I include a set of dummy variables for each week of the year to trace the temporal effects of the pandemic. This approach basically explores how the effect on sales evolves over time. This regression is specified as:

Where $Tt$ is a binary indicator equal to 1 for the year 2020 and equal to 0 otherwise while $Ww$ is a categorical variable for the 52 weeks of the year as defined by NielsenIQ. I exclude the last week of February 2020 as the reference week (9th week). All other variables are the same as previously defined.

In Figure 1, I show trends in average weekly sales of dietary supplements by product modules across retail stores for 2019 and 2020. Across all product modules, the figure reveals a notable jump in sales after the 10th week of 2020, whereas sales in 2019 appear relatively stable. The 10th week of 2020 corresponds to the week ending March 6, 2020, providing some suggestive evidence to support the idea that increased sales of dietary supplements could be attributed to the onset of COVID-19.

Sales increased substantially after the 10th week of 2020 and reached their highest peak during the 12th week, however, sales began to decline after that across all product modules. While sales generally remained higher in 2020 relative to 2019 across all the product modules, in the case of protein supplements, sales fell between the 12th and 14th weeks of 2020, below the same period in 2019. This drop could be attributed to the lockdowns that restricted movement; thus, fitness fanatics who are primary users of protein supplements (Garthe and Maughan, 2018; Maughan, 2013; Maughan et al., 2018; Pasiakos et al., 2015) may not have needed to purchase them. Nonetheless, sales of protein supplements appear to have bounced back after the period. In summary, the descriptive evidence suggests that the onset of the COVID-19 pandemic was associated with an increase in dietary supplement sales, particularly in the first few weeks of March 2020.

Also, I present results in Table 1, which tests mean differences in sales of dietary supplements across the nine defined product modules between the pre-COVID-19 period and the COVID-19 period. The findings in Table 1 reveal that, on average, sales across all dietary supplement product modules were significantly higher over the COVID-19 period compared to the pre-COVID-19 period. Taken together, the tests of mean differences also indicate a positive association between the onset of the COVID-19 pandemic and sales of dietary supplements across the U.S. I formally test these findings in the subsequent section using the described empirical framework.

Based on the specification in Equation (1), I estimate the effect of the COVID-19 pandemic on dietary supplement sales. I define the month of March 2020 as the beginning of the COVID-19 period. It is important to note that the emergence of COVID-19 cases predates March 2020, since the U.S. declared the COVID-19 outbreak a public health emergency as far back as January 31, 2020. Hence, in this case, where I study nutrition and health-related outcomes, it is possible that the effects of COVID-19 could go as far back as January 31, 2020, and even much earlier than that.

However, the decision to define March 2020 as the start of the COVID-19 pandemic is based on the fact that many significant events occurred in March 2020, including the World Health Organization's (WHO) declaration of COVID-19 as a pandemic, the emergency declaration on March 13, 2020, by the then-President of the U.S., and several states issuing stay-at-home orders. Hence, the estimates reflect the impacts of a combination of these events on dietary supplement demand across the U.S. In all the specifications, I include store, year, and week fixed effects. Since the study uses a PPML regression, the coefficients are expressed as semi-elasticities.

As presented in Table 2, I find strong evidence that suggests that demand increased substantially in the weeks of March 2020, mirroring the descriptive findings. Across all but one dietary supplement module, the PPML estimates suggest that COVID-19 had a positive impact on dietary supplement sales. In column 1 of Table 2, the results indicate that demand for nutritional supplements was about 1.01% higher during the COVID-19 period compared to the pre-COVID-19 period. This result is, however, not statistically different from zero. It appears that the sharp increase in sales of nutritional supplements observed in March 2020 may have been offset by the increased sales in the early weeks of 2020 and lower sales later on in 2020. For the remaining modules, excluding protein supplements, the results overall indicate significant increases in dietary supplement sales at the 1% level. For example, in the case of mineral supplements, the results indicate that sales increased by 15.26% over the COVID-19 period. In the case of protein supplements, the findings suggest a decrease in sales by 0.60% over the COVID-19 period. This result is, however, not statistically different from zero.

In Appendix Table A1, I present results for an alternate specification to equation (1), where I do not include week and year-fixed effects. The findings in Appendix Table A1, while largely similar to those in Table 2, indicate that sales were significantly higher across all dietary supplement modules. The differences in results between Table 2 and Appendix Table A1 indicate that there are some time-specific factors influencing sales across the nutritional supplements and protein supplements modules. The findings in Appendix Table A1 also mirror findings in Table 1, where we test mean differences in dietary supplement sales between the pre-COVID-19 period and the COVID-19 period.

I now turn to the event study style plots presented in Figure 2 based on the specification in equation (2), which I use to assess changes in dietary supplement sales before and after the 9th week across 2019 and 2020. Overall, the figure shows a clear jump in sales starting the first week of March 2020 across all dietary supplement modules. Sales reach their peak in the third week of March 2020 and begin to fall after that. While the effects in the first three weeks of March 2020 are consistent across product modules, the effects after the fourth week of March 2020 vary across all product modules. For example, in the case of protein supplements, the figure shows substantial declines after the third week. The decline in sales could be attributed to lockdowns enforced in the last weeks of March and April, which primarily hindered movement and, to a significant extent, the use of gyms and sporting facilities. This would result in lower sales of protein supplements, which are popular among athletes and active gym users looking to build muscle and improve performance. In summary, the event study plots overall point to a substantial increase in demand for dietary supplements across all product modules, mainly in the weeks of March 2020.

In this paper, I provide evidence of the impact of the COVID-19 pandemic on the demand for dietary supplements in the U.S. The use of retail scanner data to study demand allows us to better explore the dynamics of dietary supplement demand throughout the pandemic. I find evidence that overall, the weeks of March 2020 were associated with increased sales across all dietary supplement modules considered in this study.

The findings also suggest that despite a drop in sales of dietary supplements across some product modules after March 2020, demand for supplements on average remained high throughout the rest of 2020 compared to 2019. The results also seem to suggest a year-on-year increase in dietary supplement sales, which provides important insights into longer-run trends of the demand for dietary supplements, indicating the ever-growing demand for dietary supplements.

I acknowledge that the study has some limitations. Some of the different results may be driven by some nuances in how NielsenIQ classifies products into their respective modules. Additionally, I am unable to make claims about causality given the myriad of events that occurred throughout the COVID-19 pandemic that impacted the demand for dietary supplements. While the study does not explore all the specific COVID-19-related policies that may be driving the results, the findings overall suggest that across all modules, the early weeks of the COVID-19 pandemic were associated with increased sales of dietary supplements.

The findings broadly speak to the importance of the market for dietary supplements. In particular, there is a need for policymakers to pay closer attention to the regulation of dietary supplements, given their increasing use and some of the health claims associated with the use of these products. The COVID-19 pandemic has shown that many people rely on dietary supplements in such crisis periods as medication, hence, the need for improved regulation.

Researcher(s)’ own analyses calculated (or derived) based in part on data from Nielsen Consumer LLC and marketing databases provided through the NielsenIQ Datasets at the Kilts Center for Marketing Data Center at The University of Chicago Booth School of Business. The conclusions drawn from the NielsenIQ data are those of the researcher(s) and do not reflect the views of NielsenIQ. NielsenIQ is not responsible for, had no role in, and was not involved in analyzing and preparing the results reported herein.