Vitamin D has been claimed to reduce the risk of heart disease, multiple sclerosis, and even rheumatoid arthritis.
But, some scientists have also found that a vitamin D deficiency could increase the risk of developing dementia.
Earlier this year, Austrian researchers claimed people with more exposure to sunlight – a major source of vitamin D – had a lower risk of dementia.
About 850,000 people in the UK have dementia, according to the Alzheimer’s Society.
In 2014, a study claimed patients with a deficiency in vitamin D were “substantially” more at risk of developing the condition.
Adults that were moderately deficient in the vitamin had a 53 per cent high risk of getting dementia.
Those who were severely deficient were 122 per cent more likely to develop the condition, the University of Exeter scientists claimed.
The study analysed more than 1,600 people, who were followed for six years to investigate who developed Alzheimer’s disease, as well as other forms of dementia.
“We expected to find an association between low vitamin D levels and the risk of dementia and Alzheimer’s disease, but the results were surprising,” said Dr David Llewellyn at the time, a researcher working on the study.
“We actually found that the association was twice as strong as we anticipated.
“Clinical trials are now needed to establish whether eating foods such as oily fish or taking vitamin D supplements can delay or even prevent the onset of Alzheimer’s disease and dementia.”
More studies were needed to confirm the link between dementia and vitamin D, but the scientists said the findings were very encouraging.
“Even if a small number of people could benefit, this would have enormous public health implications given the devastating and costly nature of dementia,” said Llewellyn.
Another study in 2015, from the US, claimed lower vitamin D levels was linked to a decline in memory and thinking skills.
After the study, Alzheimer’s Research UK said a balanced diet and exercise was key to reducing the risk of dementia.
The charity’s Head of Research, Dr Simon Ridley, said: “Vitamin D plays an important role in keeping our bodies healthy and there are a number of studies that suggest a link between vitamin D deficiency and memory and thinking difficulties.
“While this new research suggests an association between low vitamin D levels and faster rates of memory loss, we don’t yet know whether taking supplements could stave off dementia or slow down decline in those who are already living with the condition.
“We need to see more research into this approach to understand the role vitamin D plays in dementia risk.
“A balanced diet is important for brain health and, alongside physical activity and keeping weight and blood pressure in check, can help reduce dementia risk.”