Does a lot of physical exercise prevent clogged arteries? New research suggests that this may not be the case.
Coronary artery calcification (CAC) is a condition characterized by a buildup of plaque in the main vessels that supply blood to the heart.
This condition can lead to a wealth of cardiovascular problems, including the poor circulation of blood to and from the heart, depending on the severity of plaque buildup in the arteries.
According to available data, CAC is more common in men than it is in women, and it usually develops late in life. Some populations considered to be "at risk" of developing CAC are individuals with a higher body mass index (BMI), those with hypertension, and people with chronic kidney disease.
A new study conducted by researchers from the University of Illinois at Chicago (UIC) and the Kaiser Permanente in Oakland, CA, has now looked at the impact of physical exercise on the likelihood of developing CAC.
Dr. Deepika Laddu, from the UIC, and her colleagues made some surprising findings, which were reported earlier this week in the journal Mayo Clinic Proceedings.
More exercise tied to higher risk of CAC
The team recruited 5,115 participants through the Coronary Artery Risk Development in Young Adults study between March 1985 and June 1986. The baseline cohort included both black and white men and women, all of whom were aged between 18 and 30.
Due in part to incomplete medical data, however, the final analysis was conducted on information sourced from 3,175 participants in the original cohort.
The participants were followed-up for 25 years, until 2011. They underwent eight examinations over this period and filled in questionnaires reporting their levels of physical activity on at least three of these occasions.
Participants were split into three categories, following different physical activity trajectories. These were:
- trajectory one: people who exercised for under 150 minutes (2.5 hours) per week, which is below national physical activity guidelines
- trajectory two: participants who met physical activity guidelines by exercising for 150 minutes per week
- trajectory three: people who exceeded the national physical activity guidelines by exercising for more than 450 minutes (7.5 hours) each week
Much to their surprise, the researchers found that the participants who had the highest levels of physical activity (trajectory three) were 27 percent more likely to develop CAC by middle age compared with people who exercised for under 2.5 hours per week.
"We expected to see that higher levels of physical activity over time would be associated with lower levels of CAC," admits Dr. Laddu.
White men most at risk
The development of CAC was tested for during the participants' final year in the study, when they were all aged between 43 and 55. Computerized tomography scans of the chest area were used for this purpose.
After analyzing their data in terms of race and sex, the team also found that the group at the highest risk was white men, who were 86 percent more likely to develop CAC than their counterparts.
Black men in trajectory three were not significantly at risk, and neither were women — regardless of racial background.
According to the researchers, the novelty of this study lies in the fact that it was conducted over a long period of time (25 years) so that its authors could map out the risk of CAC in relation to physical exercise patterns from the participants' young adulthood to their middle age.
"Because the study results show a significantly different level of risk between black and white participants based on long-term exercise trajectories, the data provide rationale for further investigation, especially by race, into the other biological mechanisms for CAC risk in people with very high levels of physical activity."
Dr. Deepika Laddu
Despite the study's findings, the researchers suggest that further investigation is needed to fully understand the implications.
"High levels of exercise over time may cause stress on the arteries leading to higher CAC," says paper co-author Dr. Jamal Rana, from the Kaiser Permanente, "however this plaque buildup may well be of the more stable kind, and thus less likely to rupture and cause heart attack, which was not evaluated in this study."
The new findings should not be taken as a reason to stop exercising, adds Dr. Laddu.
Following this study, the researchers are planning to investigate the likelihood of different outcomes, such as the risk of experiencing a heart attack.
The study authors conclude, "Collectively, these data suggest that the biological mechanisms associated with increased CAC and high levels of [physical activity] deserve further evaluation."
"Likewise," they add, "the impact of modestly higher levels of CAC in aging, highly active individuals on [cardiovascular] outcomes also deserves further attention."