Which dietary supplements can help prevent COVID-19?

The coronavirus disease 2019 (COVID-19) pandemic, caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) agent, has infected over 63.47 million people worldwide and has killed over 1.47 million. The World Health Organization (WHO) declared the global spread of COVID-19 a pandemic on March 11, 2020. The pandemic has been dubbed by many as the largest public health and economic crisis of a generation.

Since the first case of the infection was detected late in 2019 in Wuhan, China, numbers have risen exponentially. Nearly a year on since COVID-19’s detection, advice regarding healthy diets and dietary supplements that can prevent infection or help alleviate symptoms has been flooding social and other media. Researchers collaborating from the United Kingdom, Sweden and the United States conducted a recent study surveying population use of dietary supplements over the past few months. Their study, titled “Dietary supplements during the COVID-19 pandemic: insights from 1.4M users of the COVID Symptom Study app: A longitudinal app-based community survey,” was released in the preprint server medRxiv* on November 30, 2020.

Study: Dietary supplements during the COVID-19 pandemic. Image Credit: Farion_O / Shutterstock
Study: Dietary supplements during the COVID-19 pandemic. Image Credit: Farion_O / Shutterstock

Dietary supplements and the immune system

Since the pandemic’s beginnings, several studies have shown that micronutrients such as vitamins C and D and zinc have been known to boost the immune system and reduce the risk of respiratory infection. With SARS-CoV-2 being a respiratory infection, these nutrients have been prescribed and advised by health care professionals since the beginning of the pandemic. The authors of this study wrote that these nutrients could be obtained from diets and dietary supplements, taken alone or as part of a multinutrient or multivitamin tablet.

Several other dietary supplements are also known to benefit health and the immune system. These include omega-3 fatty acids (“fish oil”), probiotics and plant isolates like garlic, wrote the researchers. They added, “The use of specific dietary supplements in both prevention and acute treatment of infection with SARS-CoV-2 has been promoted since the beginning of the current coronavirus pandemic”.

Increasing sales and consumption

The researchers wrote that the market sales of the dietary supplements rose by 19.5 percent in the UK in the time before March 2020 when the pandemic and nationwide “lockdown” was declared. Sales of vitamin C rose by 110 percent, and multivitamin supplement sales rose by 93 percent. Zinc supplement sales rose by 415 percent over just 7 days between 2-8 March 2020 in the US. Similar rises in sales were seen with Vitamin D supplements as well.

Study objective and design

This study was a longitudinal app-based community survey. It tested participants who had subscribed to a COVID-19 symptoms based app (COVID Symptom Study app). Self-reported regular dietary supplement usage was checked. This included, “probiotics, garlic, omega-3 fatty acids (“fish oils”), multivitamins, vitamin D, vitamin C or zinc.”

The study initially attempted to examine the rate of SARS-CoV-2 infection among 327,720 UK participants and their supplement use rate. To this was added data from 45,757 US and 27,373 Swedish participants using the app. They also checked self-reported loss of smell (anosmia) in 993,365 regular app users on dietary supplements who had not been tested for the infection. Anosmia remains one of the strongest predictors of COVID-19, the researchers explained.


Overall, the researchers found that:

  • Probiotics reduced the risk of SARS-CoV-2 by 14 percent (8 to 19 percent range)
  • Omega-3 fatty acids reduced the risk of SARS-CoV-2 by 12 percent (8 to 16 percent range)
  • Multivitamins reduced the risk of SARS-CoV-2 by 13 percent (10 to 16 percent range)
  • Vitamin D reduced the risk of SARS-CoV-2 by 9 percent (6 to 12 percent range)
  • Vitamin C, zinc or garlic supplements did not significantly reduce the incidence of SARS CoV-2 infection

Next the team broke down the participant population into gender, age and body mass index (BMI) classes and found that probiotics, omega-3 fatty acids, multivitamins and vitamin D protected females of all ages and BMI from SARS-CoV-2. The same protection was not seen among men. Similar protective effects were noted for the American and Swedish populations as well. The next part of the study, which checked for protective effects of the supplements and anosmia among 993,365 regular app users, also showed a similar protective effect.

Conclusions and implications

The researchers outlined the protective roles of the supplements as follows:

  • Vitamin D – the immune cells express the vitamin D receptor, and so it plays a role in the function of antigen-presenting cells, T-cells and B-cells. The team writes, “It [vitamin D] also promotes production of cathelicidin, a microbicidal component of the innate immune system.”
  • Multivitamins – the components of these have antioxidant properties, and studies have shown they may reduce the risk of respiratory infections
  • Omega-3 fatty acids – these play a role in the function of T-cell and B-cells and are anti-inflammatory.
  • Probiotics can alter gut microbiota and may generate anti-viral metabolites that strengthen the host immune system.
  • Zinc, Vitamin C and garlic – Studies have shown that they may play a role in reducing symptoms. Similar findings were not seen in this study.

This study revealed that there is a significant protective effect of probiotics, omega-3 fatty acid, multivitamin or vitamin D supplements against SARS-CoV-2 infection. The team wrote, “No clear benefits for men were observed nor any effect of vitamin C, garlic or zinc for men or women.”

The researchers called for further randomized trials with these supplements and their combinations to check for the protective efficacy of these agents against SARS-CoV-2.

*Important Notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Journal reference:
Dr. Ananya Mandal

Written by

Dr. Ananya Mandal

Dr. Ananya Mandal is a doctor by profession, lecturer by vocation and a medical writer by passion. She specialized in Clinical Pharmacology after her bachelor's (MBBS). For her, health communication is not just writing complicated reviews for professionals but making medical knowledge understandable and available to the general public as well.


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