COVID-19 risk reduced by probiotics, omega 3s, multivitamins and vitamin D in “modest but significant” link

02 Dec 2020 --- An analysis of 300,000 UK users of the ZOE COVID Symptom Study App found that supplementation of probiotics, omega 3 fatty acids, multivitamins or vitamin D was associated with a lower risk of self-reported SARS-CoV-2 infection.

These findings stem from the largest observational study on COVID-19 and dietary supplement use to date, collected from over 1.4 million app users from the US, the UK and Sweden.

Now awaiting peer review, the international preprint study found a “modest but significant” association of these supplements and reduced COVID-19 risk in women, but not in men.

“We were surprised by the strong sexual dimorphism in the UK cohort,” corresponding author Cristina Menni from King’s College London, UK, tells NutritionInsight. “We didn’t really know what to expect.”

She was also surprised that her research team did not observe an effect for vitamin C, zinc or garlic supplements. The same overall patterns of association were observed in both US and Swedish app-using cohorts.

Caution with these findings is warranted given the study is observational and cannot determine a causal relationship. “We must now wait for randomized controlled trials,” flags Menni.

Self-reported findings
In the UK cohort, supplementation with probiotics was associated with a lower risk of testing positive for SARS-CoV-2 in 14 percent of the study participants, followed by multivitamins (13 percent), omega 3 fatty acids (12 percent) and vitamin D (9 percent).

The study’s discovery cohort included 372,720 UK app users who reported having had an RT-PCR-based or serology test for SARS-CoV-2 and who completed the app-based dietary supplement questionnaire. 

App users taking multivitamins, omega 3s, probiotics or vitamin D were less likely to be tested positive for SARS-CoV-2 in three large independent cohorts.Out of the UK app users, 175,652 self-reported using supplements regularly since the beginning of the pandemic, while 197,068 self-reported they were not.

In an independent sub-analysis, the researchers examined the extent to which supplement use was associated with self-reported anosmia – smell impairment – “the single strongest predictor of COVID-19” in 993,365 regular app users who were not tested for SARS-CoV-2.

There, “a small but significant” protective effect of around 5 percent was found for omega 3 fatty acids, multivitamins, vitamin D and to a lesser extent for probiotics overall and by gender.

To replicate significant findings from the UK cohort, the researchers used data from over 45,000 US and 27,000 Swedish app users. Overall, the UK findings were roughly mirrored in both cohorts.

Why do they work?
There are different mechanisms of actions that suggest why the four supplements had a beneficial effect on reducing the risk of COVID-19 infection.

Immune cells express the vitamin D receptor and some can synthesize the active form of vitamin D. Multivitamins often contain trace elements that have antioxidant properties and roles in supporting the immune system.

Omega 3s are “clearly demonstrated” to be anti-inflammatory, the study continues. Whether this is a mechanism by which they reduce the risk of testing positive for SARS-CoV-2, however, is not clear. 

Probiotics interact with the host’s gut-associated immune system, resulting in improved immunity and enhanced responses to the seasonal influenza vaccine. 

Vitamin C, zinc and garlic supplements showed no significant association with risk for SARS-CoV-2.Vitamin C, zinc and garlic spotlighted
On the other hand, the researchers did not find protective effects of zinc, garlic or vitamin C.

Menni highlights two speculative explanations: “Supplements are likely to affect those with low intakes of important nutrients. It may be that most participants did not have a low intake of zinc or vitamin C.” 

Moreover, it may be that zinc and vitamin C intake from supplements was insufficient to affect the immune system.

These findings are particularly interesting considering how much attention these three ingredients have been receiving in the past few months. 

A Google Trends analysis revealed that found a correlation between infection rates and search terms for “vitamin C,” “zinc,” “immune” and “garlic” in October. 

In September, a survey showed that vitamin C and zinc were viewed as high-profile, top-ranking immunity ingredients.

This study highlights a need for more randomized controlled trials of selected supplements.Not a one-stop-shop for immune health
NutritionInsight previously reported how taking supplements can provide a false sense of overall health reassurance, particularly in the case of multivitamins. 

Although supplements may be an affordable means of maintaining nutrient levels, industry experts are concerned consumers view supplements as a one-stop-shop for boosting the immune system.

“I think that supplements, in general, should be accompanied by a healthy and balanced diet. In the case of COVID-19, [they should be accompanied by] social distancing and handwashing,” says Menni. 

Her research team’s observational data serves not to provide any health recommendations but rather to highlight the need for randomized clinical trials to test the effects on COVID-19 risk and severity in clinical settings. 

“Several on vitamin D are on the way,” she notes. A UK clinical study called CoronaVit is running for six months to investigate whether the sunshine vitamin can protect against the novel coronavirus. 

This week, the UK’s Department of Health and Social Care announced it would offer free vitamin D supplements to over 2.5 million people in England deemed vulnerable to COVID-19 throughout the winter.

By Anni Schleicher