Vitamin D levels tend to be low in people living in Northern Europe during winter months.
Vitamin D is synthesised in the skin by the action of ultraviolet in sunlight. Although it is also present in the diet – particularly oily fish – synthesis in the skin is the major natural source. As a consequence many people in Northern Europe tend to have low vitamin D levels in the winter.
Vitamin D levels also tend to be low in people with chronic disorders of the gut, liver and pancreas.
Vitamin D deficiency has been shown to be common and to correlate with poorer outcomes in patients with inflammatory bowel disease. It is common in patients with undiagnosed coeliac disease, although this usually corrects on a gluten-free diet, and is also common in patients with chronic pancreatitis, and in other conditions, including liver cirrhosis where fat malabsorption occurs (vitamin D is a fat soluble vitamin).
Vitamin D is important for the immune system, not just for bones.
Vitamin D is best known for its important effects on calcium metabolism and bone formation. However, it also has important effects on the immune system. It helps macrophages (a type of white blood cell that is important in defence against bacteria and viruses) kill pathogens they have engulfed. It also has anti-inflammatory effects and has been shown to suppress the cytokine (inflammatory) response to viruses. This might be beneficial in Covid-19 where severe lung damage can result from an inflammatory “cytokine storm” in response to the virus.
Vitamin D deficiency increases risk of infection by respiratory viruses.
It has been shown that people with low vitamin D levels are more susceptible to viral respiratory infections and that regular supplementation reduces the risk.
Vitamin D supplementation might help to reduce risk of severe Covid19 illness – although there is no direct evidence to support this.
No studies of vitamin D supplementation have yet been performed in relation to Covid-19 but its protective effect against respiratory viruses and its ability in the laboratory to reduce inflammatory cytokine responses to viruses suggests that regular vitamin D supplementation might help to reduce risk of severe Covid19 illness.
If you do take vitamin D supplementation the dose is very important.
Vitamin D overdosing is harmful – it can cause dangerous increases in blood calcium and can also potentially have unwanted impacts on the immune system – dose is therefore important. Current evidence suggests that for adults a regular daily dose of 25 micrograms (1000 units) is likely to be optimal. There is good evidence that this is safe (daily doses of up to 4000 units are regarded as safe in adults). In healthy adults there is some evidence that daily dosing of more than 1000 units actually has less beneficial effect although higher doses eg 2,000 units per day may sometimes be used in patients with proven vitamin D deficiency. The National Institute for Health and Care Excellence (NICE) already recommends that all UK adults should take 400 units daily – evidence in relation to respiratory infections currently suggests that a somewhat higher dose of 1000 units per day (for adults) may be optimal.
- most UK adults are vitamin D deficient in the winter months.
- Vitamin D deficiency is particularly common in people with chronic disorders of the intestine, pancreas or liver.
- Regular daily dosing of vitamin D3 1,000 units without calcium (typically one capsule or tablet) is safe and usually sufficient to correct this
- Low levels of vitamin D are associated with increased risk of respiratory viral infection
- Vitamin D supplementation has been shown to reduce risk of respiratory viral infection
- Laboratory studies show that vitamin D reduces the cytokine response to respiratory viruses – this might be helpful in reducing the risk of serious lung damage in Covid19 infection, although this is unproven.
Note – Guts UK is a UK Charity and has no commercial links with suppliers of vitamin D.