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Monday, June 18, 2012

Exercise and genotype affect cognition


It's well established that exercise can affect mental as well as physical capacities. However, your genotype (genetic makeup) may play a surprisingly large role in determining just how much influence exercise can have on your cognitive abilities. David Bucci and his colleagues from Dartmouth College ran some experiments to demonstrate this fact.

Fifty-four healthy, sedentary young adults completed their study. All participants underwent genetic testing to determine which type of brain-derived neurotrophic factor (BDNF) they hadBDNF, a protein involved in stimulating neuron growth and known to increase with exercise (at least in rats) comes in various flavors, or alleles. The most common alleles encode either a valine (Val) or a methionine (Met) at position 66 of the protein. A single base pair change in the DNA determines which of these types of BDNF a person will make.

On day one of the study, volunteers were assessed for physical fitness. They were then given a ‘novel object recognition’ (NOR) test that consisted of two parts. First, they were shown a set of 50 images, one by one. They next took a fifteen-minute break to fill out a mental health questionnaire. Finally, they were shown 100 images, half of which they had seen before and half of which were brand new pictures. Their task was to distinguish between the two.

The participants were then divided into groups and told to return in four weeks. One group was instructed to continue not exercising at all (control). A second group was asked to exercise for at least 30 minutes four times a week. This group was further divided into two, one of which also exercised on the final test day (4W+) and one of which did not exercise that day (4W-). A last group remained sedentary for the entire four weeks but did exercise on the final test day (0W+). The participants all wore pedometers to prevent cheating.

Four weeks later, physical fitness exams and NOR tests were repeated. The only group to show improvement in the final NOR test was the 4W+ group. These were the people who had exercised for four weeks and on test day. It’s no great surprise that regular exercise improves cognitive function. But here’s the fascinating part. When the 4W+ group was further divided by genotype, it turned out that only those who were homozygous for the Val allele (meaning neither of their two copies of BDNF contained methionine at position 66) showed improvement. Met carriers did not show improvement.

The 4W+ group did accrue other benefits, such as lowered stress levels, regardless of genotype. I don’t think the take home lesson from this experiment should be, ‘don’t bother exercising if you have a BDNF Met gene.’ However, knowing how one’s genotype can affect one’s health might lead to more personalized exercise regimens.