Researchers caution against ‘misinformation’ on vitamin D during COVID-19 pandemic
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There is no evidence to suggest very high doses of vitamin D can prevent or treat COVID-19, and individuals with limited access to sunlight should consider a supplement while adhering to a healthy lifestyle, researchers report.
In a consensus paper published in BMJ Nutrition, Prevention & Health, researchers advised the population to adhere to their respective government’s guidance on vitamin D supplementation, even during periods of self-isolation that accompany the pandemic, when time spent outdoors may be limited.
“Popular information channels, such as social media platforms, continue to be rife with misinformation, particularly with respect to vitamin D,” Susan Lanham-New, PhD, FRSB, FAfN, professor of human nutrition and head of the nutritional sciences department at the University of Surrey in the United Kingdom, told Healio. “We consider it very important to get sound, scientific messages on the nutritional aspects of immune function, and in particular with respect to COVID-19. It is critical during this pandemic that advice given to the public is accurate, evidence-based and timely; anything less could mislead and has the potential to cause harm.”
Mechanisms questioned
Controversy remains as to whether there is a direct link between the seasonality of upper respiratory tract infections, influenza and vitamin D deficiency; higher influenza incidence in winter may be due to behavioral reasons, such as more time spent indoors, the researchers wrote.
“Nonetheless, vitamin D appears to inhibit pulmonary inflammatory responses while enhancing innate defense mechanisms against respiratory pathogens,” the researchers wrote. “Moreover, population-based studies show positive associations between circulating 25-OHD concentration and lung function. Nevertheless, formal systematic reviews/meta-analyses of these associations are urgently required.”
The researchers wrote that widespread calls for high-dose vitamin D supplementation during the pandemic are without support from pertinent studies in humans and instead are “based on speculations about presumed mechanisms.”
“The discovery of the expression of nuclear vitamin D receptors and vitamin D metabolic enzymes in immune cells provides a scientific rationale for the potential role of vitamin D in maintaining immune homeostasis,” Lanham-New said. “However, there is insufficient scientific evidence to support claims that high-dose vitamin D supplementation will be effective in preventing or treating Covid-19 disease.”
Researchers noted that studies suggest ethnic minorities are disproportionately affected with Covid-19 and further research is justified, given “clear evidence” that vitamin D deficiency is particularly common among ethnic minority groups.
“However, we strongly caution against doses higher than the upper limit (4,000 IU/day; 100 μg/day) and certainly of very high doses of vitamin D (in some reports, 10,000 IU/day; 250 μg/day of vitamin D are being promoted) unless under personal medical advice/clinical advice by a qualified health professional,” the researchers wrote.
Ensure a healthy diet
A nutritionally balanced diet that includes vitamin D-rich foods, such as oily fish, red meat, egg yolk and fortified milk, along with safe sunlight exposure, remain the best ways to avoid vitamin D deficiency, the researchers wrote.
The researchers acknowledged that low vitamin D status may be exacerbated during the COVID-19 pandemic, and anyone who is self-isolating with limited access to sunlight is advised to take a vitamin D supplement according to their government’s recommendations for the general population.
“Currently, there is no robust, scientific evidence to show that very high vitamin D intakes will be beneficial in preventing or treating COVID-19 disease, but avoidance of vitamin D deficiency is essential for health,” Lanham-New said.
For more information:
Susan Lanham-New, PhD, FRSB, FAfN, can be reached at the University of Surrey, Guildford, Nutritional Sciences Department, GU2 7XH, United Kingdom; email: s.lanham-new@surrey.ac.uk
Editor’s Note: This article was changed on June 5 to indicate the recommended upper limit for vitamin D supplementation is 4,000 IU/day (100 μg/day). The editors regret the error.
Perspective
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JoAnn E. Manson, MD, DrPH, FACE, FAHA
The COVID-19 pandemic should increase awareness of the importance of avoiding vitamin D deficiency. Whether or not vitamin D is directly involved in reducing risk for COVID infection or severity of the disease, we already know that vitamin D deficiency increases risk for bone and musculoskeletal disorders, as well as cardiometabolic disorders. But there are also several lines of evidence implicating vitamin D deficiency in increased susceptibility to COVID infection and risk of poor clinical outcomes from the infection. We know that adequate vitamin D status is important to innate immunity and having a robust immune response to viral respiratory infections. Vitamin D may also have immune-modulating effects such as tamping down inflammation, which may be relevant to the COVID-related cytokine storm and related respiratory distress.
In observational studies, there has been evidence for a long time that patients with viral infections have lower 25-hydroxyvitamin D levels, although that could be due to confounding factors or effects of the illness on the biomarker. Recent studies during the pandemic suggest that people with severe COVID-19 illness do tend to have low 25-hydroxyvitamin D blood levels, and those who have vitamin D deficiency are about 8 times more likely to develop severe illness vs. those who are vitamin D sufficient. Importantly, a meta-analysis of 25 randomized trials prior to the COVID pandemic demonstrated that vitamin D supplementation reduced the risk for acute respiratory tract infections, with particularly pronounced benefits (70% reduction) among those with profound vitamin D deficiency (Martineau AR, et al. BMJ. 2017; doi:10.1136/bmj.i6583.). We plan to explore the potential role of vitamin D in COVID-19 by conducting a randomized controlled trial of vitamin D supplementation among patients recently diagnosed with COVID-19, to see if it can reduce risk for developing severe illness or the need for hospitalization. We will also assess whether supplementation can reduce the risk of developing the infection in household contacts of people with the infection.
The potential link between vitamin D deficiency and COVID-19 risk does not mean that everyone should run out to get screened for their blood level of 25-hydroxyvitamin D. It is also not a call for mega-dose vitamin D supplementation. However, it is a call for heightened awareness to avoid vitamin D deficiency by readily achievable measures, including getting outdoors for physical activity and incidental sun exposure, with all the usual precautions, and seeking dietary sources of vitamin D, including fortified foods, such as cereals and dairy products, and fatty fish. Whether or not vitamin D directly affects COVID-19 risk, these measures will provide musculoskeletal and other health benefits. For those who cannot get outdoors or get adequate vitamin D in their diet, a vitamin D supplement of 1,000 IU or 2,000 IU per day, especially during this pandemic, is reasonable. Thus, a call to action for population-based measures to reduce vitamin D deficiency appears indicated at this challenging time.
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