16th February 2017
Many stories in the headlines today suggest that vitamin D from supplements or fortified foods could prevent colds. This is based on a systematic review of studies looking at the effect of vitamin D supplementation on acute respiratory tract infections, published today in the BMJ, which found a small but significant reduction in risk in those given vitamin D supplements.
The authors say that their findings “support the introduction of public health measures such as food fortification to improve vitamin D status in settings where profound vitamin D deficiency is common.” National surveys show that about 1 in 5 people in the population have low vitamin D levels in the blood, so what should be done to improve our vitamin D status?
The evidence on vitamin D and health was reviewed in depth by the Scientific Advisory Committee on Nutrition in their report published in 2016 and, based on this, the Government now recommends that everyone aged 5 and over should consider a vitamin D supplement (10 µg per day) from October to March (when we can’t make vitamin D from sun exposure), and has provided supplement advice for younger children and other population groups. People with very little or no sunshine exposure are advised to take a daily supplement containing 10 µg vitamin D throughout the year. This includes those who are seldom outdoors such as frail or housebound individuals and those who are confined indoors (e.g. in institutions such as care homes) and people who habitually wear clothes that cover most of their skin while outdoors. People from minority ethnic groups with dark skin such as those of African, African-Caribbean and South Asian origin, are also advised to consider taking a daily supplement containing 10 µg vitamin D throughout the year. For more information see our page on Government advice on vitamin D.
While it is acknowledged that vitamin D contributes to the normal function of the immune system (there is a European health claim to this effect), there are differing views within the scientific community on the strength of evidence for an effect of vitamin D on prevention of colds. Public Health England has stated that there is insufficient evidence to support recommending vitamin D to reduce the risk of respiratory tract infections. In the case of this particular systematic review the effect of vitamin D on risk of infections was relatively small there was a lot of variability in the results of studies included. In addition, previous systematic reviews on this topic have had mixed results, with some finding a similar association and others showing no effect. This is discussed in more detail in an editorial included in the BMJ. To support a healthy immune system a range of nutrients from a healthy balanced diet, including vitamin D, are needed.
We already have advice for supplementation in place, which is based on strong evidence for the importance of vitamin D in bone health. Some countries, including the US and Finland have vitamin D fortification policies in place, whereas others, including the UK have voluntary fortification. Foods fortified in the UK include spreads, breakfast cereals and yogurts and these make a contribution to our intakes, but it is difficult to get all the vitamin D we need from the diet alone.
BNF has developed a resource showing the vitamin D content of different foods and how vitamin D requirements can be met, available here.