麻豆传媒

Lack of vitamin D may put elderly people at increased risk of dementia or Alzheimer鈥檚 disease, a study of 1658 American adults has concluded.

The study is the largest ever to investigate possible links between vitamin D deficiency and dementia, and confirms the findings of earlier, smaller studies.

鈥淲e expected to find an association between low vitamin D levels and the risk of dementia and Alzheimer鈥檚 disease, but the results were surprising as we actually found that the association was twice as strong as we expected,鈥� says of the University of Exeter Medical School in the UK, and head of the study team.

Llewellyn and his colleagues followed the participants, whose average age at the outset was 74, for six years to observe how many developed heart disease, dementia or strokes during that time. The amount of vitamin D in their blood was measured once, at the start of the study.

In all, 171 people developed a type of dementia, which in 102 cases was Alzheimer鈥檚 disease. Participants whose blood contained the lowest levels of vitamin D had a disproportionately higher risk of developing both dementia and Alzheimer鈥檚.

After the six years, participants severely deficient in vitamin D 鈥� defined as having less than 10 micrograms of the vitamin per litre of their blood 鈥� were 122 per cent more likely to have Alzheimer鈥檚 and 125 per cent more likely to have other forms of dementia than those whose blood contained sufficient amounts. This was defined as having a blood concentration level of more than 20 micrograms per litre, as recommended by the US Institute of Medicine.

Those moderately deficient in the vitamin, with corresponding blood levels between 10 and 20 micrograms per litre, were 59 per cent more likely to develop dementia and 69 per cent more likely to develop Alzheimer鈥檚.

Protective effect?

Llewellyn warns that the study does not prove that vitamin D protects against the diseases, or that a lack of it causes them. Further trials are needed, he says, to see if raising a person鈥檚 blood concentrations of vitamin D above 20 micrograms per litre of blood reduces their risk of disease.

In the summer, exposure to around 15 minutes of sunlight a day typically generates enough vitamin D. Otherwise, people can consume extra amounts in oily fish and supplements. The UK National Health Service recommends that .

鈥淰itamin D is essential for keeping our bodies healthy, and although these results don鈥檛 suggest people should start dosing up on supplements, it鈥檚 important for people to ensure they are getting enough vitamin D,鈥� says Simon Ridley, head of research at the charity, .

Ridley says that other ways to lower the risk of dementia include eating healthily, exercising regularly and keeping blood pressure and weight down. Inflammatory conditions such as diabetes, obesity and atherosclerosis can also contribute, and a recent pilot trial of etanercept, a drug that combats inflammation, showed promising signs of halting progression in Alzheimer鈥檚 disease although again, much larger trials are needed to validate the initial findings.

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