For years we've been told vitamin d will help build strong bones. Now we're finding out that it may also help to protect our brains. A new British study finds not getting enough vitamin d may double your risk of developing dementia and Alzheimer's disease.

"They looked at people, who were initially, not demented, had no major medical issues going on, in their mid-70's, measured their vitamin D levels and then followed them over time. What they saw was those who had lower vitamin D levels, at that time when everybody was relatively normal, that group was at higher risk for developing dementia five years later," said Cleveland Clinic Neurologist Dr. James Leverenz, who did not take part in the study.

Researchers at the University of Exeter Medical School studied the blood samples of nearly 1,600 elderly people. They were dementia-free when they initially had their vitamin D levels checked.

Nearly six years later, they found people with low levels of vitamin D had a 53 percent increased risk of developing dementia. And, those who were severely deficient had a 125 percent increased risk compared to those with normal vitamin D levels.

Researchers say more studies are needed to determine if diet or supplements can help delay the onset of Alzheimer's disease and dementia. Leverenz says if you're wondering about your vitamin D level, start with your doctor.

"It's reasonable to go to your doctor to have your vitamin D level checked and if it's low to have it supplemented. There's some evidence that if your levels are normal, supplementing it is unlikely to help, so I think mostly we want to identify those people who have lower levels and actually get them on supplementation," Leverenz said.

Complete findings for this study can be found online in the journal Neurology.