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  • Writer's pictureDr Joanne Delange

New Data Released - Can Dietary Supplements affect SARS-CoV-2 Risk?

An observational study has been published in BMJ Nutrition, Prevention and Health investigating the effects of dietary supplements on the risk of testing positive for SARS-CoV-2, using data from the COVID-19 Symptom Study app.

The COVID-19 Symptom Study app, also known as the ZOE app, was developed by Kings College London (KCL) and launched in March 2020 in the UK, the USA and Sweden. The aim of the app was to collate self-reported information and to track symptoms in a large number of people to understand the epidemiology of the virus and track the evolution of the COVID-19 pandemic.

A number of scientific reviews and research publications have now been published focusing on the role of diet and specific nutrients in the immune system, some of which have focused on respiratory viral infections. Nutritional Insights investigated some of the main findings of these studies in a paper published in BMJ Nutrition, Prevention and Health last year.

Scientists from KCL used the data from their app to investigate whether supplements might be associated with a lower risk of catching SARS-CoV-2. They analysed information from 372,720 people in the UK, and around 75,000 from Sweden and the USA, regarding their regular use of dietary supplements throughout May, June, and July 2020. In addition, they compared these data with whether these people tested positive for SARS-CoV-2.

The scientists observed that, for women taking probiotics, omega-3 fatty acids, multivitamins or vitamin D had a moderate, but significant, lower risk of catching SARS-CoV-2. However, no clear benefit was found for men. In addition, no effect was seen for people taking vitamin C, zinc or garlic supplements.

The protective associations in women who were taking probiotics, omega-3 fatty acids, multivitamins and vitamin D were observed across all ages and BMI groups. The same overall pattern of association was observed in both the US and Swedish cohorts.

One major limitation of this study, or any observational study, is that there will be many other differences between the people taking part in the study who took or didn't take a supplement, apart from the difference in supplement use. That means that any one, or more, of these other differences could have been the reason that different rates of positive SARS-CoV-2 test were observed – and not the supplements at all. These other differences are called 'confounders'.

Where the data was analysed and adjusted for confounders, including underlying conditions and usual diet, the risk of SAR-CoV-2 infection was reduced by 14% for women taking probiotics, 12% for women taking omega-3 fatty acids, 13% for women taking multivitamins and 9% for women taking vitamin D.

However, randomised controlled trials are essential to confirm these observational findings before any therapeutic recommendations can be made.


Louca P, Murray B, Klaser K, et al (2021). Modest effects of dietary supplements during the COVID-19 pandemic: insights from 445 850 users of the COVID-19 Symptom Study app. BMJ Nutrition, Prevention & Health 2021. Available at:

Derbyshire EJ and Delange J (2021). COVID-19: is there a role for immunonutrition, particularly in the over 65s? BMJ Nutrition, Prevention & Health 2020. Available at:

COVID Symptom Study. Available at:



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