In contrast with previous research, a study published in the Journal of Alzheimer’s Disease indicates that exercise in midlife is not associated with cognitive fitness in late life. The data suggest that physical activity may not help maintain cognitive function or prevent the onset of Alzheimer’s disease. Physical activity in late life, however, is associated with high cognitive function two years later, according to the researchers.
The literature contains few prospective data on the relationship between midlife and late-life physical activity and late-life cognitive performance. Cross-sectional study designs and short durations of follow-up have made several studies of this relationship unsatisfactory, according to Alden L. Gross, PhD, Assistant Professor of Epidemiology at Johns Hopkins Bloomberg School of Public Health in Baltimore, and colleagues.
A Prospective Study of Medical Graduates
To conduct a prospective analysis of the possible association between exercise in midlife and cognitive performance in later life, Dr. Gross and colleagues examined 30 years of longitudinal data from the Johns Hopkins Precursors study. This study enrolled medical graduates from 1948 to 1964 and followed them annually with health questionnaires. Surveys of physical activity were mailed in 1978, 1986, 1989, 1993, 1995, 1997, 2003, and 2006. Participants underwent cognitive testing in 2005 and 2008.
An adjudication committee consisting of physicians assigned diagnoses of dementia and dates of onset based on participants’ medical records. The investigators assigned a metabolic equivalent value (MET) to each category of activity (ie, vigorous, moderate, light, and sleep). They used linear regression for cognitive tests and Cox proportional hazards models for dementia onset to characterize associations with midlife physical activity. Models were adjusted for age, sex, smoking, diabetes, and hypertension.
Exercise Had No Long-Term Cognitive Effects
The study sample included 646 participants (48 women). In 1978, participants’ mean age was 47, mean BMI was 23.7 kg/m2, the prevalence of hypertension was 8.8%, and the prevalence of diabetes was 0.8%. Approximately 74% of participants reported regular exercise. In 2006, 54% of participants had hypertension, and 12% had diabetes. The incidence of dementia was 4.3%, and mean age at onset was 77.
No measure of activity in 1978, including MET h/day, decile of physical activity, and engagement in regular exercise, was associated with cognitive performance in demographic-adjusted or fully adjusted models. Regular exercise in 2006 and MET h/day expended in 2006, however, were associated with better cognitive performance. In addition, no physical activity exposure in 1978 was associated with onset of dementia. Greater physical activity in 2006, however, had a modest inverse association with risk of dementia.
The strength of the association between cognitive outcomes and physical activity in 1978 did not vary by gender. In 2006, however, greater MET h/day in a typical week and regular exercise were significantly associated with better cognitive performance in women, but not in men.
Homogeneous Sample Reduced Confounders
Previous studies included diverse cross sections of people and thus may have been susceptible to residual confounding by factors such as years of education, said the investigators. The Precursors study represents a highly homogeneous sample, however, which reduces the likelihood of such confounding. Nevertheless, the homogenous sample may limit the results’ generalizability, particularly to women.
“The prevailing notion that higher levels of physical activity protect against cognitive impairment in later life may result from the artifact of reverse causation,” said the authors. “While physical activity is strongly recommended for many reasons, our data suggest cognitive health may not be one of those reasons.”
“These findings have implications for intervention work moving forward,” said Dr. Gross. “We still need to focus on causes and mechanisms of Alzheimer’s [disease] and dementia, since we do not yet know which preventive measures may or may not work. For now, when I speak in the community about Alzheimer’s [disease], I find that people take some relief in understanding that there was not anything that anyone might have done to avoid a loved one developing Alzheimer’s [disease]. Of course, the goal for researchers is to identify factors that may help older people maintain their cognitive function into their later years. More long-term studies like the Precursors study are needed.”
—Erik Greb
Suggested Reading
Gross AL, Lu H, Meoni L, et al. Physical activity in midlife is not associated with cognitive health in later life among cognitively normal older adults. J Alzheimers Dis. 2017;59(4):1349-1358.
