The researchers classified participants as being cognitively impaired if they scored in the worst 10 percent of older adults in the study. They found that the odds of cognitive impairment were about 42 percent higher in those people who were deficient in vitamin D, and 394 percent higher in people who were severely deficient.

"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," Llewellyn said. "Given that both vitamin D deficiency and dementia are common throughout the world, this is a major public health concern."

According to Llewellyn, the majority of older U.S. adults have insufficient vitamin D levels because skin becomes less efficient at producing vitamin D with age and sunlight (UVB radiation) levels are limited for much of the year.

"Vitamin D supplements have proven to be a safe, inexpensive and effective way to treat deficiency. 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," Llewellyn said.

Antioxidant “Rich Diet with Walnuts Improves Memory and Learning in Alzheimer's Mice

It has been suggested that oxidative stress may have a key role in Alzheimer's disease. Oxidative stress occurs when the production of free radicals exceeds the antioxidant capacity of a cell. Reports have suggested that beta amyloid can increase oxidative stress leading to brain cell death.

Walnuts are source of alpha-linolenic acid (a plant-based omega-3 fatty acid) and have high content of antioxidants. In March 2004, the U.S. Food and Drug Administration said that "Supportive but not conclusive research shows that eating 1.5 ounces of walnuts per day, as part of a low saturated fat and low-cholesterol diet, and not resulting in increased caloric intake, may reduce the risk of coronary heart disease."

Abha Chauhan, PhD, and colleagues at the New York State Institute for Basic Research in Developmental Disabilities, examined the effect of diet containing 6 percent or 9 percent walnuts (equivalent to 1 oz. and 1.5 oz. daily intake of walnuts in people) on the cognitive, emotional and motor functions in a transgenic mouse model of Alzheimer's. The mice were fed custom-mix diets from the age of four months for nine to 15 months. Control mice were fed diet without walnuts. The experimental and control mice were examined at the age of 13 to 14 months and 18 to 19 months for spatial memory and learning ability, position discrimination learning ability, motor coordination, and anxiety-related behavior.

The researchers found that Alzheimer's transgenic mice on the diet without walnuts at both testing periods showed memory deficits, anxiety-related behavior, and severe impairment in spatial learning ability, position discrimination learning ability and motor coordination. The Alzheimer's transgenic mice on 6 percent walnuts diet and 9 percent walnuts diet showed significant improvement in learning, memory, emotional regulation and motor coordination compared to transgenic mice that did not eat walnuts.  The effects of 6 percent and 9 percent walnuts diets were similar.

"Our results suggest protective effects of walnuts in the Alzheimer's mice," Chauhan said. "Dietary supplementation of walnuts may have beneficial effect on brain function, and deserves further study."

SOURCE Alzheimer's Association