Older people with a vitamin D deficiency are more likely to develop dementia or Alzheimer’s, according to a new study.

About five million adults in the U.S. suffer from Alzheimer’s, with approximately 500,000 of them dying from the disease each year, according to the Alzheimer’s Association.

An international team of researchers at the University of Exeter Medical School discovered that participants of the study who where severely lacking in vitamin D had a 125 percent increase in the risk of suffering from dementia and Alzheimer’s. Those who were moderately lacking in vitamin D levels were 53 percent more likely to develop the diseases.

The study, led by Dr David Llewellyn, analyzed elderly individuals in the U.S. as part of the Cardiovascular Health Study. The researchers looked at 1,658 adults aged 65 years and older who were free from dementia and cardiovascular disease at the beginning of the study. After following the participants for six years, the researchers found a significant link between the lack of adequate vitamin D levels and developing dementia and Alzheimer’s.

“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 Llewellyn in a statement.

The findings of the study are published in the online issue of Neurology, the medical journal of the American Academy of Neurology.