It’s not too late to top up on vitamin D if you ignored advice issued last year by Public Health England (PHE) to take supplements. But while the PHE recommended we all “consider” taking 10µg of vitamin D daily during autumn and winter, researchers are now suggesting that food be fortified with the vitamin so that we can take it continuously. The main source of vitamin D is sunlight in contact with the skin – and that is pretty much never between November and April, hence the PHE’s recommendation.
Vitamin D is also available in oily fish (wild salmon or herring), liver, egg yolks and some fortified bread, but nearly a quarter of adults and 22% of children have low levels of the vitamin in their blood. Vitamin D is essential for healthy bones, teeth and muscles.
Professor Adrian Martineau – lead author of research in last week’s BMJ showing that vitamin D supplements reduce the risk of acute respiratory tract infections – says that fortifying foods would reduce deaths. Acute respiratory infections cause symptoms such as sore throat, fever, cough and sneezing, but can also include more serious conditions such as pneumonia. Martineau’s study, which included data from 11,000 people, found most benefit in people with seriously low levels of the vitamin.
In another paper, in Plos One, Dr Zaki Hassan-Smith, a consultant endocrinologist at the University of Birmingham, found that vitamin D may improve muscle strength. Vitamin D deficiency is known to prevent calcium being deposited in bone, causing rickets (bowing of the bones) and osteomalacia – conditions that make bones soft – and it was these conditions that most concerned PHE.
But you only need supplements if you are deficient in vitamin D. A BMJ editorial accompanying Martineau’s study said that supplements only reduced the proportion of people catching acute respiratory infections from 42% to 40%, so it may not be worth taking vitamin D every day to prevent an occasional cold. Hassan-Smith says that, for many of the proposed benefits, the jury is still out. “It is still contentious,” he says. “We are waiting for large randomised trials to report their findings.”
If you are in an at-risk group (you have darker skin, don’t go outside often, cover up when you are outside, are pregnant or are four years old or under), then you should do what the PHE says. For everyone else, 10 micrograms of vitamin D isn’t much but, folic acid aside (a supplement that pregnant women take to reduce the risk of their baby having neural tube defects such as spina bifida), the story of supplements is generally that those who benefit most are the companies that make them.