Older adults who are severely deficient of Vitamin D may be twice as likely to develop Alzheimer's Disease than those who aren't deficient in Vitamin D, a study published Wednesday found.

This was the largest study of its kind and its results were published in the journal of Neurology.

"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," noted lead researcher David Llewellyn of the University of Exeter Medical School in a news release. 

Several years' worth of data were looked at on over 1,600 Americans aged 65 or older. Llewellyn and his team found that those who were moderately deficient of vitamin D had a 53 percent risk of developing dementia. Those who were severely deficient of vitamin D had a 125 percent risk of developing dementia. Similar results were found for patients that develop Alzheimer's 69 percent for those with a moderate deficiency of vitamin D and 122 percent for those with a severe deficiency of vitamin D.

"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," Llewellyn told Yahoo. "We need to be cautious at this early stage, and our latest results do not demonstrate that low vitamin D levels cause dementia. That said, our findings are very encouraging, and even if a small number of people could benefit, this would have enormous public health implications given the devastating and costly nature of dementia." 

Right now, more than 5 million Americans are living with Alzheimer's Disease and it's the sixth-leading cause of death in the country, according to the Alzheimer's Association in Chicago.

Researchers aren't quite sure why there is a link between vitamin D and Alzheimer's. One hypothesis notes that the part of the brain that breaks down first when Alzheimer's hits the brain is full of vitamin D receptors.

Studies in France and Austrailia show that those who took vitamin D supplements had improved memories.

"People tend to not believe vitamin D news, because it seems too good to be true," John Cannell, MD, executive director of the California-based nonprofit Vitamin D Council, told Yahoo Health. "But vitamin D has a profound mechanism of action, as it's really a steroid hormone that turns genes on and off, and no other vitamin works that way."