The risk of small brain infarcts was lower by about 40% in older people who reported high levels of physical activity, researchers said.
After adjusting for demographic and cardiovascular risk factors, the odds ratio for subclinical brain infarcts was 0.6 (95% CI 0.4 to 0.9) in older patients in the highest quartile of metabolic-equivalent (MET) scores, relative to participants in the bottom half of leisure time physical activity, according to Joshua Z. Willey, MD, MS, of Columbia University in New York City, and colleagues.
The upper quartile of MET scores indicates moderate to heavy exercise, the researchers explained online in Neurology.
“Engaging in physical activity may be an important strategy to reduce the prevalence of subclinical brain infarcts and thus, potentially, improve functional outcomes,” Willey and colleagues wrote.
But the benefit appeared to be restricted to those in the highest bracket of MET scores, they pointed out — study participants who exercised only lightly (the third quartile of MET scores) had the same risk of small strokes as those in the lower two quartiles.
The study involved members of the Northern Manhattan Study cohort, which first enrolled participants in 1993. The cohort eventually reached 3,298 people older than 55 at recruitment, who were then followed to examine risks of stroke and other vascular outcomes as influenced by other medical and socioeconomic factors.
The current analysis focused on those who had not been diagnosed clinically with ischemic stroke. They were subjected to MRI scans to identify those who had experienced subclinical brain infarcts.
A total of 1,238 people were included, including 199 who lived with cohort members but had not been part of the study previously. Participants’ mean age was 70; about two-thirds were Hispanic and 60% were women.
In addition to the MRI scans, participants were questioned in person about their leisure-time physical activity using a questionnaire adapted from the National Health Interview Survey. It asked about the duration and frequency of various activities during the previous two weeks.
They were also asked if they engaged in any physical activity during the past two weeks, with those answering “no” — 43% of the sample — listed as physically inactive.
Willey and colleagues performed two sets of comparisons: one using these sedentary individuals as the reference group, the other setting the reference as participants in the bottom two quartiles of activity.
The findings were essentially the same in both sets: individuals engaging frequently in relatively intense activities such as racquetball and hiking had significantly lower rates of small brain infarcts.
Participants with MET scores higher than 14 were in the upper quartile, whereas scores of 3 to 14 were the third quartile.
The researchers also defined exercise intensity categories of light, moderate, and heavy, on the basis of MET scores of 1 to 5.5, 5.5 to 8, and greater than 8, respectively.
Some 36% of participants engaged in light-intensity exercise and 21% reported activity qualifying as moderate or heavy.
In a statistical model adjusting for age, sex, race, education, insurance status, and cardiovascular risk factors, Willey and colleagues calculated the following odds ratios for silent brain infarcts:
- Upper quartile of MET score versus lowest two quartiles: OR 0.6 (95% CI 0.4 to 0.9)
- Third quartile of MET score versus lowest two quartiles: OR 1.0 (95% CI 0.7 to 1.4)
- Moderate-heavy activity versus no activity: OR 0.6 (95% CI 0.4 to 0.9)
- Light activity versus no activity: OR 0.8 (95% CI 0.6 to 1.2)
- Any activity versus no activity: OR 0.8 (95% CI 0.5 to 1.1)
But, complicating the findings somewhat, the researchers found no association between relative physical activity and total white matter hyperintensity volume as measured with MRI.
Willey and colleagues indicated that these brain abnormalities, although commonly the result of ischemic events, can have a variety of other causes too.
“While these changes can occur with chronic cerebral ischemia, nonarteriolar and nonischemic mechanisms for white matter hyperintensities have also been proposed, including endothelial dysfunction and venous sclerosis with subsequent venous hypertension,” they wrote.
The signs of small brain infarcts on MRI are less ambiguous, Willey and colleagues suggested.
Another odd finding was that insurance status appeared to affect the strength of the association between activity and silent infarcts.
Highly active participants who were on Medicaid or without health insurance showed the same risk for these infarcts as did inactive participants. In contrast, the odds ratio for infarcts among highly active participants with private insurance or Medicare coverage was 0.4 (95% CI 0.2 to 0.7).
No definitive explanation was possible with the available data, but Willey and colleagues suggested one possibility.
“It may be that the overall adverse life experience for those who are uninsured or have Medicaid mitigates the protective effect of leisure-time physical activity. It is likely that being uninsured or having Medicaid is a reflection of lower socioeconomic status and is consistent with the extensive literature on social status being associated with a higher risk of cardiovascular disease independently of access to care,” the researchers wrote.
Limitations to the study included a lapse of several years between collecting the risk-factor data and performing the MRI scans, a lack of direct measures of physical fitness, and reliance on participants’ reports of activity levels.