Researchers have found that low levels of vitamin D doubled or even tripled the rate of cognitive decline in 382 men and women over the age of 60.

Lack of vitamin D greatly accelerates the loss of mental ability that comes with age, a study has shown.

Researchers found that low levels of the vitamin doubled or even tripled the rate of cognitive decline in 382 men and women over the age of 60.

A majority, 61 per cent, had insufficient vitamin D in their blood.

Lead researcher Professor Joshua Miller, from Rutgers University in the US, said: "There were some people in the study who had low vitamin D who didn't decline at all and some people with adequate vitamin D who declined quickly. But on average, people with low vitamin D declined two to three times as fast as those with adequate vitamin D."

The progress of participants was monitored over eight years between 2002 and 2010.

Vitamin D is mainly generated in the skin through exposure to the sun but can also be found in certain foods.

The vitamin is essential for strong healthy bones but also has important roles in nerve and muscle function, cell growth, the immune system and combating inflammation.

Prof Miller recommended that over-60s consult their doctors about taking vitamin D supplements.

"Some people may have had melanoma (malignant skin cancer) or fear getting it, or they may live in climates where the sun isn't powerful enough, or do work that keeps them out of the sun," he said.

"That's where supplements come in."

The findings are published in the Journal of the American Medical Association - Neurology.

Dr Simon Ridley, chief scientist at Alzheimer's Research UK, 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."