'Heart Healthy' Diet And Ongoing, Moderate Physical Activity May Protect Against Cognitive Decline

My bet is that it has more to do with exercise than what people eat. Since correlation does not equal causation, it's still too hard to isolate the contribution each plays.

'Heart Healthy' Diet And Ongoing, Moderate Physical Activity May Protect Against Cognitive Decline:
"ScienceDaily (July 20, 2009) — Eating a 'heart healthy' diet and maintaining or increasing participation in moderate physical activity may help preserve our memory and thinking abilities as we age, according to new research reported July 14 at the Alzheimer's Association 2009 International Conference on Alzheimer's Disease (ICAD 2009) in Vienna.
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Studies have found that older adults who are physically active may experience slower rates of cognitive decline. Less is known about the impact of changes in physical activity levels on rate of cognitive decline.
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Alzheimer's Risk Gene May Reduce Benefits of Physical Activity to Cognitive Ability

While the relationship of physical activity with cognitive performance as we age is a subject of considerable research, much less is known about how this relationship is impacted by the Alzheimer's risk gene Apolipoprotein E (APOE). The APOE gene comes in three types, or alleles, known as e2, e3, and e4. Each person gets one type of APOE from each parent, making the possible combinations: e2/e2, e2/e3, e2/e4, e3/e3, e3/e4, e4/e4. Having two copies of e4 conveys the highest risk for Alzheimer's; having one e4 also raises one's risk. E3 is the most common type. E2, though rare, is thought to be protective.

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n their analysis, the researchers found that physical activity was associated with enhanced cognitive function, and that this relationship was differentially influenced by the person's APOE genotype: non-E4 carriers and people with one copy of E4 performed better than people with two copies of E4. After adjusting for age, ethnicity, severe chronic medical illness, lean body mass, and education, aerobic physical activity continued to show a statistically significant association with cognitive function in non-E4 carriers but not in people with E4 (any combination)

"In our nationally representative sample, persons who reported higher levels of aerobic physical activity had better memory than those who reported no such activity. This was especially true in those people who didn't have the APOE-e4 Alzheimer's risk gene," Obisesan said.

"Because physical activity is a low-cost, low-risk, readily available intervention, it may prove to be an important public health strategy to reduce or prevent memory loss and other symptoms of mental decline in the elderly. Future rigorous clinical trials are needed to confirm these findings," Obisesan added.