Vitamin D may reduce women's risk of developing Alzheimer's disease, according to new research.

Researchers from two new studies found that women who don't have enough vitamin D in middle age are at greater risk of cognitive impairment and swift mental decline compared to women with adequate levels of vitamin D.

Vitamin D is an essential vitamin people get from eating foods like fatty fish, butter and cheese and drinking fortified milk. The body is also capable of making its own vitamin D when it is exposed to the sun.

The first study, lead by Dr. Yelena Slinin of the VA Medical Center in Minneapolis, found that women with low vitamin D intake were more likely to experience cognitive decline.

Slinin and her team analyzed the vitamin levels of 6,257 women who participated in the Study of Osteopathic Fractures. The women had also undergone mental ability tests known as the Mini-Mental State Examination and/or Trail Making Test Part B.

Researchers found that women with very low levels of vitamin D at less than 10 nanograms per milliliter of blood serum were more likely to have cognitive impairment at baseline, and low vitamin D levels, or less than 20 nanograms per milliliter, among women who were cognitively impaired, was associated with a higher risk of mental decline.

The second study led by Dr. Cedric Annweiler of Angers University Hospital in France looked at data from 489 women who participated in the Toulouse cohort of the Epidemiology of Osteoporosis study.

Annweiler and his team found that women who developed Alzheimer's disease had had lower vitamin D intake compared to women who did not develop the neurological disease.

Results of the study showed that women who developed the disease had an average vitamin D intake of 50.3 micrograms a week. Researchers found that women who developed other forms of dementias had an average of 63.6 micrograms per week and those who did not develop dementia at all averaged 59 micrograms a week.

Both of the studies were published in The Journals of Gerontology. Researchers say that latest findings highlight the importance of getting enough vitamin D, either through food, supplements or exposure to the sun.