In this case, the researchers looked at blood levels of vitamin D, which includes vitamin D from food, supplements and sun exposure. Dietary vitamin D can be found in fatty fish, such as salmon, and in milk, eggs and cheese.
The scientists examined 1,658 people over the age of 65 who were dementia-free. The researchers tested the vitamin D blood levels of these participants and then followed up with them on a regular basis. After an average of six years, 171 participants developed dementia and 102 volunteers had Alzheimer's disease.
What was more interesting was that those with lower levels of vitamin D were about 70 percent more likely to develop Alzheimer's disease. Those with a severe deficiency were over 120 percent more likely to develop the disease.
"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-we actually found that the association was twice as strong as we anticipated," said David Llewellyn, one of the researchers, in a news release.
In fact, the findings remained the same even after the researchers adjusted for other factors that could affect the risk of dementia, including education, smoking and alcohol consumption. The research reveals that it's crucial for those who are older to get the sufficient amount of vitamin D.