Studies support association of physical activity, diet with maintaining cognitive ability, reducing dementia risk

- Also, Antioxidant–Rich Diet Improves Memory and Learning in Alzheimer's Mice -

Evidence from three long-term, large-scale studies supports the association of physical activity and certain dietary elements (tea, vitamin D) with possibly maintaining cognitive ability and reducing dementia risk in older adults, according to new research presented today at the Alzheimer's Association International Conference on Alzheimer's Disease 2010 (AAICAD 2010) in Honolulu, HI.

Plus, a new study in an animal model of Alzheimer's reported today at AAICAD 2010 suggests that an antioxidant-rich diet with walnuts may benefit brain function.

"Research has pointed us towards a number of factors that may impact our risk of Alzheimer's and cognitive decline, the strongest being reducing cardiovascular risk factors," said William Thies, PhD, Chief Medical and Scientific Officer at the Alzheimer's Association. "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 are some of the first reports of this type in Alzheimer's, and that is encouraging, but it is not yet definitive evidence," Thies continued. "Longitudinal studies and clinical trials are expensive, and I'm deeply concerned that the trials we need will not happen because of the chronic underfunding of Alzheimer research by the federal government."

Framingham Study Shows Physical Activity Lowers Risk of Dementia, Especially in Men

Several long-term epidemiological studies have related physical activity and cognitive decline, dementia and/or Alzheimer's disease, although the results of published research studies thus far are not entirely consistent and several large studies failed to show an association. Most of these studies followed participants for less than six years or had significant loss to follow-up. Still needed are studies including long-term follow-up in older persons in age brackets at higher risk of incident Alzheimer's to elucidate the true relationship.

One such long-term trial is the Framingham Study, a population-based study that has followed participants residing in the town of Framingham, Massachusetts since 1948 for cardiovascular risk factors, and is now also tracking cognitive performance. Framingham is widely acknowledged as a premier longitudinal study; it has continued to yield valuable information for more than 40 years.

Zaldy Tan, MD, MPH, of Brigham and Women's Hospital, GRECC, VA Boston, and Harvard Medical School, and colleagues estimated the levels of 24-hour physical activity of more than 1,200 elderly participants from the Framingham Study (742 female; age 76 +\-5) during the study's 20th examination cycle (1986-87) and followed them for the development of dementia. They divided the participants into five groups based on level of physical activity, from lowest (Q1) to highest (Q5).

Over two decades of follow-up (mean 9.9 +/-5 years), 242 participants developed dementia (of which 193 were Alzheimer's). The researchers found that participants who performed moderate to heavy levels of physical activity had about a 40 percent lower risk of developing any type of dementia. Further, people who reported the lowest levels of physical activity were 45 percent more likely to develop any type of dementia compared to those who reported higher levels of activity. Similar results were seen when analyses were limited to Alzheimer's alone. Analyses showed that the observed associations were largely evident in men in the study.

"This is the first study to follow a large group of individuals for this long a period of time," Tan said. "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."

Tea Consumption Slows Cognitive Decline in the Cardiovascular Health Study

Observational studies have shown associations between consumption of either tea or coffee and cognitive function in older adults, but data including long-term follow-up and rate of change in cognitive function are lacking.

Lenore Arab, PhD, of UCLA, and colleagues used data on more than 4,800 men and women aged 65 and older from the Cardiovascular Health Study to examine the relationship between consumption of tea, coffee, and change in cognitive function over time. Study participants were followed up for up to 14 years for naturally-occurring cognitive decline using the Mini-Mental State Examination (3MSE) administered at baseline and annually up to 8 times. People scored on the average 1.17 points less per year. Tea and coffee drinking were assessed using a food frequency questionnaire.

The researchers found that people who consumed tea at a variety of levels had significantly less cognitive decline (17-37 percent) than non-tea drinkers. More specifically, study participants who drank tea 5-10 times/year, 1-3 times/month, 1-4 times/week, and 5+ times/week had average annual rates of decline 17 percent, 32 percent, 37 percent, and 26 percent lower, respectively, than non-tea drinkers.

According to the scientists, coffee consumption did not show any effect except at the very highest level of consumption – where it was associated with significantly decreased decline of 20 percent.

"The suggestion of a positive effect of tea consumption in slowing cognitive decline requires further investigation," Arab said. "Interestingly, the observed associations are unlikely to be related to caffeine, which is present in coffee at levels 2-3 times higher than in tea."

Vitamin D Deficiency Increases Risk of Cognitive Impairment

Recent European studies suggest vitamin D deficiency is associated with increased odds of cognitive impairment and dementia in later life, although previous findings from the U.S. have been mixed. Interest in vitamin D has intensified recently as research has suggested that it may play a role in a variety of age-associated diseases.

David Llewellyn, PhD, of the University of Exeter Peninsula Medical School (UK), and colleagues examined information from 3,325 adults aged 65 years and older from the Third National Health and Nutrition Examination Survey (NHANES III), a study that was carefully designed to accurately represent the U.S. non-institutionalized population. Vitamin D levels were measured from blood samples and compared with performance on a measure of general cognitive function that incorporated tests of memory, orientation in time and space, and ability to maintain attention.

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."