Evidence for the health benefits of vitamin D is inconclusive, scientists have found.
Their results contrast with previous reports claiming that vitamin D supplements can improve bone mineral density and reduce the risk of fractures or falls in older people.
Researchers led by the University of Edinburgh reviewed hundreds of studies on the subject to reach their conclusion.
The team identified 137 different health conditions that have been linked to vitamin D levels. These include bone disorders, multiple sclerosis, autoimmune diseases, cancer and heart problems.
They found that vitamin D - produced either through exposure to sunlight or ingested from taking supplements - might offer protection from several health conditions. However universal conclusions about its benefits cannot be drawn, the researchers say.
The findings did suggest a link between a mother’s vitamin D levels in late pregnancy and the birth weight of her child.
The researchers also concluded that there is ‘probably’ a link between vitamin D and dental caries in children.
Only ten of the conditions have been tested both in observational studies - which investigate possible links between vitamin D levels and the disease - and in clinical trials.
Better designed studies and randomised clinical trials are needed to draw firm conclusions about the possible health benefits of vitamin D, the review concluded.
Vitamin D deficiency is a concern for people living at high latitudes, where there is little daylight in winter, and people who spend a lot of time indoors are also at risk. It is important to clarify whether there is a true link between vitamin D deficiency and disease.
The review was carried out by researchers at the University of Edinburgh, Imperial College London, Trinity College Dublin and Stanford University. The findings are published today in the British Medical Journal.