TUESDAY, Oct. 25 (HealthDay News) -- Researchers have identified a gene variation that seems to have a major effect on the rate at which men experience an age-related decline in intellectual function.

The study included 144 experienced U.S. male pilots over the age of 40 who took a Federal Aviation Administration-approved flight simulator test three times over two years. The participants included recreational pilots, certified flight instructors and airline pilots.

Using blood and saliva samples from the pilots, the researchers also conducted genetic analyses, looking for the gene that produces a protein called brain-derived neurotropic factor (BDNF). The BDNF gene is considered critical to the development and maintenance of the central nervous system. Levels decline gradually with age, but the findings of this study suggest that a variant of the gene hastens that process.

To test their theory, the researchers divided the pilots into two groups -- those with at least one copy of a BDNF gene that contained the methionine, or "met," variant and those without the variant.

Previous research has linked the "met" variant with increased risk of depression, stroke, anorexia nervosa, anxiety-related disorders, schizophrenia and suicidal behavior.

The flight simulator test scores of pilots in both groups fell over the three-year study period, but the rate of decline in the "met" group was much steeper, said the researchers at the Stanford University School of Medicine and the Veterans Affairs Palo Alto Health Care System.

"We saw a doubling of the rate of decline in performance on the exam among met carriers during the first two years of follow-up," study senior author Dr. Ahmad Salehi, a clinical associate professor of psychiatry and behavioral sciences at Stanford, said in a university news release.

Using MRI scans, the researchers also found that pilots with the "met" variant showed significant age-related decline in the hippocampus, a brain area that's crucial to memory and spatial reasoning.

"This gene-associated difference may apply not only to pilots but also to the general public, for example in the ability to operate complex machinery," Salehi said.

The study was published online Oct. 18 in the journal Translational Psychiatry.

Staying active can help maintain healthy BDNF levels, the researchers said. "The one clearly established way to ensure increased BDNF levels in your brain is physical activity," Salehi said.

More information

The Society for Neuroscience offers an overview of aging and the brain.