Vitamin D in winter: the NHS advice and the studies
The NHS says some groups, including all children aged 1 to 4, should take a daily supplement all year round, not just in the colder months.
Between October and early March the body does not make enough vitamin D from sunlight, the NHS says, and government advice is that everyone should consider taking a daily supplement during the autumn and winter.
Vitamin D helps regulate the calcium and phosphate in the body, nutrients that keep bones, teeth and muscles healthy. A lack of it can lead to bone deformities such as rickets in children, the page adds.
The daily amount is 10 micrograms for adults and for children from the age of one. The same dose appears on supplement labels as 400 International Units (IU).
Who is advised to take it all year
The Department of Health and Social Care recommends a daily supplement of 10 micrograms throughout the year for adults and children over four who:
- are not often outdoors, for example because they are frail or housebound
- live in an institution such as a care home
- usually wear clothes that cover up most of their skin when outdoors
People with dark skin may also not make enough from sunlight, and should consider a supplement all year, the page says. Children aged 1 to 4 should be given one all year too.
More is not better. Too many supplements over a long period can build up calcium in the body, which can weaken the bones and damage the kidneys and the heart. The upper limit for adults is 100 micrograms (4,000 IU) a day. For children aged 1 to 10 it is 50 micrograms (2,000 IU) a day.
What the studies show
Separately from the NHS advice, an analysis in the BMJ in 2017 pooled 25 trials in which people were given vitamin D or a dummy treatment. It found that vitamin D reduced the risk of sudden infections of the airways overall. The protection was seen in people taking daily or weekly doses, but not in those given large one-off doses.
A Cochrane review of 56 trials with 95,286 participants, published in 2014, looked at deaths instead. Of people given vitamin D, 12.5% died during the trials, against 12.7% of those who were not. The review’s authors said vitamin D3 “seemed to decrease mortality in elderly people living independently or in institutional care.”
Both pieces of work come with limits. Most people in the Cochrane trials were women older than 70, and more than 8% of participants dropped out. The authors said further placebo-controlled trials “seem warranted.”
The NHS also says some medical conditions mean people may not be able to safely take as much vitamin D, and that anyone in doubt should consult a doctor.
