Elderly people who are not getting enough vitamin D may be doubling their risk of developing dementia and Alzheimer's disease, according to a new study.

An international team of researchers looked at the vitamin D levels of 1,658 individuals who were over the age of 65 and dementia-free. After an average of six years, 171 participants developed dementia. That number includes 102 people who were specifically diagnosed with Alzheimer's disease.

The study, published Wednesday in the online issue of Neurology, showed that those with low levels of vitamin D had an increased risk of developing dementia, while those who were severely deficient had a 125 per cent increased risk compared to those who had normal levels of vitamin D.

People with low levels of vitamin D were nearly 70 per cent more likely to develop Alzheimer's disease, while those who were severely deficient were more than 120 per cent more likely to develop the disease.

The study considered low levels of vitamin D to be below 50 nanomoles per litre, a measure used in various medical test reports.

"It's quite worrying when you consider how many older adults in the U.S. and other countries have low levels of vitamin D," study author David Llewellyn told CTV News.

Vitamin D is often called the "sunshine vitamin," as the body makes it when the skin is exposed to the sun.

It’s also found in fatty fish such as salmon, tuna or mackerel and milk, eggs and cheese.

Llewellyn said clinical trials are now needed to determine whether eating foods that have high levels of the vitamin or taking a supplement can prevent the onset of the disease.

He pointed out that the majority of older adults in the northern hemisphere can't produce vitamin D through much of the year because of a lack of sunshine.

"Unless you eat a huge amount of fish, you are likely to be deficient for large periods of the year," Llewellyn said.

According to the Alzheimer Society of Canada, 747,000 Canadians were living with dementia in 2011, and that number is expected to rise to 1.4 million by 2031.

While it's too early to say whether increased vitamin D intake could prevent dementia, generally leading a healthy lifestyle is the key to preventing several diseases, said McMaster University biochemist Cynthia Balion.

"Having a healthy diet and eating things that have vitamin D in it like fish, eggs and fortified food like cheeses, are great things," she said.

Balion added that outdoor exercise also increases sun exposure.

"What I can say for certainty is having a healthy lifestyle is a good thing. Healthy in terms of eating, exercising and socializing," she said. "Particularly as you age to continue doing those things you did when you were younger."

With a report from CTV’s medical specialist Avis Favaro and producer Elizabeth St. Philip