Vitamin D for COVID-19? Researchers flag dangers of over-supplementation

22 May 2020 --- A new consensus paper warns against taking large doses of vitamin D as a way to address COVID-19. This stance comes as other researchers in recent weeks have previously called for supplementation above the Recommended Dietary Allowance (RDA), albeit within recommended upper safety limits. Nonetheless, the latest paper also focalizes the importance of avoiding vitamin D deficiency, as many people are spending more time indoors than usual.

“The continued spread of the novel SARS-CoV-2 virus – and the disease it causes, COVID-19 – has led to calls for widespread high-dose vitamin D supplementation, but currently there is not the evidence to support this. There are no vitamin D randomized controlled trials looking at the effect of vitamin D against COVID-19 prevention or recovery. Until these are published, we can only look at the scientific evidence in observational studies, of which there are very few,” Susan Lanham-New, lead study author and Professor of Human Nutrition and Head of Nutritional Sciences Department at The University of Surrey, tells NutritionInsight. 

Written along with other researchers from Europe and the US, Lanham-New’s consensus paper advises that consumers adhere to Public Health England (PHE) guidance on supplementation, as too much can lead to an increase in calcium levels in the blood. However, Lanham-New stresses the importance of avoiding vitamin D deficiency, which stops the body from functioning properly, as well as lowering immune protection. “There is not enough evidence to say that having a high vitamin D status is protective. However, not being vitamin D deficient is certainly important for health generally,” she states. 

Nonetheless, there have been a few mechanistic studies in a similar vein. Lanham-New points to a recent analysis of vitamin D and viral infections, as well as an unbiased screening of repurposed drugs for treatment of avian influenza A H5N1 virus using appropriate cell lines and mice, which highlighted calcitriol (the active hormone of vitamin D) as a potential therapy. 

“However, whether these mechanisms apply to SARS-CoV-2 is not known. Given that ethnic minorities are disproportionately affected with COVID-19 – and this appears to be the case principally in the US, UK and other European countries – further research is justified, especially given that there is clear evidence that vitamin D deficiency is particularly common in these ethnic groups,” she notes. 

Lanham-New details that during the lockdown, it is key that people try to achieve sunlight exposure without leaving home, such as by spending time in a garden or on a balcony. People with darker complexions will find it more challenging than paler people to gain the exposure requirements in the Northern hemisphere. Therefore, she recommends the consumption of a nutritionally balanced diet, including vitamin D-rich foods, as well as supplements for those who are self-isolating. 

People should consume a nutritionally balanced diet, including vitamin D-rich foods.Lacking evidence 
The researchers also investigated the purported link between vitamin D levels and respiratory tract infections in general. Previous studies in this area have found that lower vitamin D status is associated with acute respiratory tract infections, but limitations of the findings of these studies were identified. The majority of the prior studies used data gathered from population groups in developing countries and cannot be extrapolated to populations from more developed countries due to external factors. Therefore, the researchers believe that there is currently no firm link between vitamin D intake and resistance to respiratory tract infections.

The paper, which has been published in BMJ, Nutrition, Prevention and Health, follows unverified reports that doses of vitamin D higher than 4,000 IU per day reduce the risk of contracting COVID-19 and can be used to treat the virus successfully. This has had a trickle-down effect on industry marketing, with the US Food and Drug Administration (FDA) most recently warning Life Unlearned against misrepresenting or implying that its vitamin D products can mitigate, prevent, treat, diagnose, or cure COVID-19 in people. This follows a spate of crackdowns on companies making similar COVID-19 claims. 

A deviation from prior calls
Commenting on Lanham-New’s study, Manfred Eggersdorfer of the Department of Internal Medicine at University Medical Center Groningen, tells NutritionInsight that it contains a lot of “positive messages,” including the role that good nutrition and lifestyle factors have on immune function. However, he is a co-author of a separate study calling for consumers to take extra doses of vitamin D. Published in Nutrients, it examines the optimal nutritional status for a well-functioning immune system as part of protecting against viral infections including COVID-19. 

The researchers of this study concluded that supplementation above the RDA but within recommended upper safety limits is warranted for nutrients including vitamins C and D. They state that supplementation of various micronutrients and omega 3 fatty acids is a safe, effective and low-cost strategy to help support optimal immune function. The researchers also encouraged public health officials to include nutritional strategies in their recommendations to improve public health. 

Eggersdorfer explains that supplementation can help to eliminate nutritional gaps and support optimal immune function, and therefore reduce the risk and consequences of infections.

“Higher doses can be required for shorter periods to fill the gap if a person has a low vitamin D status. Several recent meta-analyses have concluded that vitamin D supplementation reduces the risk of respiratory tract infections in both children and adults. Protective effects were seen with those receiving daily or weekly vitamin D, but not with less frequent bolus doses. A daily intake of 2000 IU is recommended in these publications. This is above the daily recommendation of 600-800 IU (depending on age), but below the TUL for those over one year of age (2,500-4,000 IU),” he explains. 

However, he agrees with Lanham-New that there are no studies yet examining vitamin D supplementation for COVID-19. “We can build on the study results reported in the different meta-analyses, which showed a benefit of supplementation with 2000 IU vitamin D per day. Overall, good nutritional status of vitamin D is very important in supporting the immune system to combat coronavirus if infected.”

Last month, NutritionInsight also reported that some researchers were calling for “urgent supplementation” of 20-50 µg vitamin D per day in vulnerable groups, which could then be “quickly extended” to the general adult population. This was in light of one review observing that the outbreak occurred in winter in the Northern hemisphere, as well as another highlighting that the molecular virulence mechanism dipeptidyl peptidase-4 receptor (DPP-4/CD26) binding has been identified in the MERS virus, which is closely related to COVID-19. 

By Katherine Durrell