Young, white men who exercise excessively face risk for subclinical atherosclerosis

Young, white men could be at risk for plaque buildup and future subclinical atherosclerosis if they’re extremely active, a new study published in Mayo Clinic Proceedings reports.

Deepika R. Laddu, PhD, and colleagues at the University of Illinois at Chicago spent 25 years surveying 3,175 patients about their exercise habits in an effort to expand the current body of information about physical activity (PA) and future cardiovascular risk. All patients, drawn from the Coronary Artery Risk Development in Young Adults (CARDIA) study, were interviewed eight times over the course of the more than two-decades trial, guided by a questionnaire about their activity levels, including participation in recreational sports, home maintenance, occupational activities and exercise.

Laddu and colleagues aimed to examine the effects of long-term physical activity patterns and their association with subclinical atherosclerosis. To do this, the researchers measured participants’ coronary artery calcification (CAC) levels, since CAC is a strong predictor of incident coronary heart disease.

While, in past studies, high levels of cardiorespiratory fitness have been linked to lower levels of CAC in the future and a minimized risk of cardiovascular disease, Laddu and co-authors wrote the connection between exercise and coronary subclinical atherosclerosis hasn’t ever been explored in a population as its members age. Members of the CARDIA study were followed from 1985 through 2011.

Laddu and her team used computed tomography to measure CAC levels in all participants, who were an average of 25 years old at the study’s baseline. Group-based trajectory modeling helped the researchers identify physical activity trajectories as the cohort aged.

National guidelines, including 2008’s Physical Activity Guidelines for Americans, emphasize the benefits of moderate- to vigorous-intensity exercise on a regular basis to reduce the risk of cardiovascular disease. In accordance with such guidelines, Laddu and colleagues divided their study population into three groups: those whose activity levels were below PA guidelines, those whose exercise habits met PA guidelines and a smaller cohort who exceeded PA guidelines by three times the amount of physical activity recommended.

Scientists are still unsure of the exact line between too much and too little exercise for promoting optimal cardiovascular health, and it remains a hotly debated topic in the field, Laddu and co-authors wrote.

Although the team hypothesized higher levels of physical activity would result in lower levels of CAC 25 years later, they found that patients who exercised the most vigorously and often were at the highest risk for subclinical atherosclerosis. White men, especially younger men, were at the highest odds for developing the adverse condition, and while similar trends were expressed in white women, they were nonsignificant. According to the research, black participants who fell into the excessive exercise category saw no higher odds of developing dangerous levels of CAC or atherosclerosis.

“The results of the present study showing a relationship between higher doses of PA and CAC development suggest yet another possible mechanistic explanation for the existence of an upper limit for CV benefit,” Laddu and co-authors wrote. “However, it may also be possible that higher PA engagement confers atherosclerotic benefit by promoting plaque stabilization and preventing its rupture, leading to thrombosis.”

The researchers also noted that recent studies of healthy, middle-aged adults have shown a similar trend in heightened doses of exercise and higher levels of CAC. In those cases, though, the atherosclerotic benefit of physical activity could actually be preventing calcified plaques from rupturing.

“In essence, there’s a lot that we don’t know,” Ludu said in an online video accompanying the study. “How this relates to the clinical world is that maybe we should just pay a little bit more attention to looking at atherosclerotic risk, even among those who are exercising, and especially among those who are exercising at higher doses.”

She noted, however, that she doesn’t want anyone to think exercise is negative.

“At the end of the day, exercise is medicine, and I really don’t want people who read this paper to think this is distracting away from that message," Ludu said. "The benefits of exercise are indisputable, and it is still one of the best primary or secondary prevention methods that should be prescribed and should be practiced. But what this data does suggest is that maybe there is an upper threshold for (the benefits) of physical activity.”