Scientists from the UK, Europe and the US, including experts from the University of Birmingham, have published a vitamin D consensus paper warning against high doses of vitamin D supplementation.
According to the study, there is currently insufficient scientific evidence to show that vitamin D can be beneficial in preventing or treating Covid-19. The authors advise that the people adhere to public health guidance regarding vitamin D supplementation.
Following unverified reports that high doses of vitamin D (higher than the current safe upper limit of 4000 IU per day) could reduce the risk of contracting Covid-19 and be used to successfully treat the virus, the researchers investigated the current scientific evidence base on vitamin D and its use in treating infections.
Vitamin D is a hormone, produced in the skin during exposure to sunlight, and helps regulate the amount of calcium and phosphate in the body, which are needed to keep bones, teeth and muscles healthy. An adequate level of vitamin D in the body is crucial to overall health, too little can lead to rickets or the development of osteoporosis and too much can lead to an increase in calcium levels in the blood which could be particularly harmful.
No evidence for vitamin D fighting COVID-19
The scientists found no evidence of a link between high dose vitamin D supplementation in helping to prevent or treat Covid-19 and cautioned against over supplementation of the vitamin, without medical supervision, due to health risks. Vitamin D is a fat-soluble nutrient and can build up in the body.
Weak link between vitamin D status and respiratory tract infections
The researchers concluded that claims about the benefit of vitamin D in treating the virus are not supported by adequate human studies and are based on findings from studies that did not specifically investigate this.
Reports of a link between vitamin D blood levels and respiratory tract infections were also examined by scientists. Previous studies have found that lower vitamin D status is associated with acute respiratory tract infections. However, findings from most of studies were based on data gathered from population groups in developing countries and cannot be extrapolated to populations from more developed countries.
Scientists believe that there is currently no firm link between vitamin D intake and resistance to respiratory tract infections.
One researcher stated that most of our vitamin D comes from exposure to sunlight, but for many people, particularly those who are self-isolating with limited access to sunlight during the current pandemic, getting enough vitamin D may be a real challenge. Supplementing with vitamin D is recommended but should be done under the current public health guidelines.
How much vitamin D?
The current vitamin D recommendation is based on how much we need to protect bones. Osteoporosis Canada advises that Canadian adults get 800 to 2,000 IU (international units) of vitamin D from a supplement year-round to maintain a sufficient level of the nutrient in the bloodstream.
Some people, though, might need more to maintain a sufficient blood vitamin D level. The safe upper limit is 4,000 IU per day.
Very few foods contain vitamin D naturally; salmon and tuna are among the best sources. Fluid milk, many non-dairy milks and some brands of orange juice are fortified with the vitamin.
Source: BMJ Nutrition, Prevention & Health online, May 2020.
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