WASHINGTON – Couch-potato time in youth may reach far into a person’s future, doubling the risk of cognitive decline in older years.
Data extracted from a 25-year-long cardiovascular risk study show that individuals who get less than the recommended amount of exercise and also sit in front of a TV for hours were twice as likely to experience cognitive decline as were those who had one individual factor, Dr. Kristine Yaffe said at the Alzheimer’s Association International Conference 2015.
“This pattern of low physical activity and sedentary behavior is associated with worse cognitive function even in midlife,” said Dr. Yaffe of the University of California, San Francisco. “It sets the stage for what happens over the next 20-30 years.”
It’s an especially important message for young people, who are spending more and more time in front of electronic devices and simultaneously decreasing time for physical exercise, said Dr. Yaffe, who presented the data on behalf of her colleague, Tina Hoang of the Northern California Institute of Research and Education, San Francisco.
Ms. Tina Hoang
“We all need to understand that physical activity is not just important for our weight and heart, but also for our brain. This needs to be a public health issue,” Dr. Yaffe said.
She presented a subanalysis of the CARDIA study (Coronary Artery Risk Development in Young Adults). CARDIA examines the development and determinants of clinical and subclinical cardiovascular disease and its risk factors. It began in 1985 with about 5,000 subjects aged 18-30 years. They have been followed regularly since then.
The CARDIA subanalysis comprised 3,375 individuals who had undergone three cognitive tests at the end of their follow-up periods: the Stroop Test of color naming, the Digit Symbol Substitution Test (DSST), and the Rey Auditory Verbal Learning Test (RAVLT). At each visit, subjects completed a questionnaire that assessed physical activity and television viewing over time.
Long-term patterns of low physical activity (approximately less than 300 calories per 50-minute session, three times a week) occurred in 17%, and long-term patterns of high TV viewing (at least 4 hours daily) in 11%. The investigators compared these groups to those who had neither activity pattern in multivariate regression analyses that controlled for age, race, gender, education, smoking, alcohol use, body mass index, and hypertension.
At the end of their follow-up, people who sustained a low physical activity pattern but did not have high TV viewing were almost twice as likely to have declined on both the DSST and Stroop (odds ratios, 1.82 and 1.38, respectively). The RAVLT was not significantly affected.
Those with high TV viewing alone were also significantly more likely to show cognitive decline on the DSST and Stroop (OR, 1.34 and 1.61, respectively). Again, the RAVLT was not significantly affected.
The group was then trichotomized according to activity level. Both those in the high- and intermediate-activity groups enjoyed what Dr. Yaffe called “a modest protective effect” against dementia. The combination of low physical activity and lots of TV time, which occurred in 3% of patients in the subanalysis, more than doubled the odds for cognitive decline on the Stroop and DSST (OR, 2.45 and 2.38, respectively).
There are likely two mechanisms of protection in the high and intermediate activity groups, Dr. Yaffe said. One seems intuitive: Exercise reduces the risk of atherosclerosis, which occurs not only in coronary vessels but in the brain’s vasculature as well.
The other is more abstruse.
“We know from rodent models, which are now backed up by human imaging results, that physical exercise increases plasticity in the hippocampus, preserving volume. Physical activity seems to have a direct effect on the hippocampus.”
The National Heart, Lung, and Blood Institute sponsors the CARDIA study. Neither Dr. Yaffe nor Ms. Hoang had any relevant financial disclosures.