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SUNDAY, July 11 (HealthDay News) -- Physical activity and adequate levels of vitamin D appear to reduce the risk of cognitive decline and dementia, according to two large, long-term studies scheduled to be presented Sunday at the International Conference on Alzheimer's Disease in Hawaii.
In one study, researchers analyzed data from more than 1,200 people in their 70s enrolled in the Framingham Study. The study, which has followed people in the town of Framingham, Mass., since 1948, tracked the participants for cardiovascular health and is now also tracking their cognitive health.
The physical activity levels of the 1,200 participants were assessed in 1986-1987. Over two decades of follow-up, 242 of the participants developed dementia, including 193 cases of Alzheimer's.
Those who did moderate to heavy amounts of exercise had about a 40 percent reduced risk of developing any type of dementia. People with the lowest levels of physical activity were 45 percent more likely to develop any type of dementia than those who did the most exercise. These trends were strongest in men.
"This is the first study to follow a large group of individuals for this long a period of time. It suggests that lowering the risk for dementia may be one additional benefit of maintaining at least moderate physical activity, even into the eighth decade of life," study author Dr. Zaldy Tan, of Brigham and Women's Hospital, VA Boston and Harvard Medical School, said in an Alzheimer's Association news release.
The second study found a link between vitamin D deficiency and increased risk of cognitive impairment and dementia later in life.
Researchers in the United Kingdom analyzed data from 3,325 people aged 65 and older who took part in the third U.S. National Health and Nutrition Examination Survey. The participants' vitamin D levels were measured from blood samples and compared with their performance on a measure of cognitive function that included tests of memory, orientation in time and space, and ability to maintain attention. Those who scored in the lowest 10 percent were classified as being cognitively impaired.
The study found that the risk of cognitive impairment was 42 percent higher in people who were deficient in vitamin D, and 394 percent higher in those with severe vitamin D deficiency.
"It appears that the odds of cognitive impairment increase as vitamin D levels go down, which is consistent with the findings of previous European studies. Given that both vitamin D deficiency and dementia are common throughout the world, this a major public health concern," study author David Llewellyn, of the University of Exeter Peninsula Medical School, said in the news release.
Skin naturally produces vitamin D when exposed to sunlight. However, most older adults in the United States have insufficient vitamin D levels because skin becomes less efficient at producing vitamin D as people age and there's limited sunlight for much of the year.
"Vitamin D supplements have proven to be a safe, inexpensive and effective way to treat deficiency," Llewellyn said. "However, few foods contain vitamin D and levels of supplementation in the U.S. are currently inadequate. More research is urgently needed to establish whether vitamin D supplementation has therapeutic potential for dementia."
Previous research has pointed to a number of factors that may be associated with cognitive decline and Alzheimer's, especially cardiovascular risk factors, said William Thies, chief medical and scientific officer at the Alzheimer's Association.
He added that "the Alzheimer's Association and others have repeatedly called for longer-term, larger-scale research studies to clarify the roles that these factors play in the health of the aging brain."
These new studies "are some of the first reports of this type in Alzheimer's, and that is encouraging, but it is not yet definitive evidence," Thies said in the news release.
The U.S. National Institute on Aging has more about Alzheimer's disease.