Low levels of physical activity in young adults may account for a “substantial” proportion of high blood pressure incidence over time, researchers report in Hypertension: Journal of the American Heart Association.
The 20-year observational study, conducted by scientists at Northwestern University Feinberg School of Medicine in Chicago, Ill., involved 4,618 white and African-American men and women taking part in the Coronary Artery Risk Development in Young Adults (CARDIA) Study. “High blood pressure is known to develop over many years and is due to many factors including diet, health behaviors and genetics,” said Mercedes Carnethon, Ph.D., study lead author and assistant professor of preventive medicine at Feinberg.
“Our study measures a comprehensive set of these health risk factors over 20 years — making this one of the longest follow-up studies to test whether activity and fitness are associated with hypertension development.” The study confirms and extends earlier findings that linked fitness and hypertension “by showing that fitness during young adulthood — a time when cardiovascular disease risk factor burden is typically low — is an important indicator of hypertension development in middle age,” Carnethon said.Low fitness has a stronger association with the development of hypertension than low self-reported physical activity, yet the two appear to have independent effects, researchers said.
Fitness is a precise measure obtained from treadmill duration testing. Activity was assessed with an interviewer administrated self-reported questionnaire and thus imprecise, but is associated with hypertension development, researchers said. The researchers measured blood pressure and estimated fitness levels based on the duration of exercise treadmill tests conducted in young adults 18 to 30 years old in 1985.
The participants were re-examined after two, five, seven, 10, 15 and 20 years. Researchers found:
* Hypertension incidence (blood pressure over 140/90 millimeters of mercury) was 13.8 per 1,000 person-years (this information was found by taking the number of new cases within a specified time period divided by the size of the population initially at risk).
* Low fitness was significantly associated with the increased risk of developing hypertension with each tertile (third) of increased physical activity after adjusting for smoking, age, sex, race, cholesterol, diet and other factors.
* The “preventive fraction,” the estimated proportion of hypertension that could be prevented if participants moved to a higher fitness category, was 34 percent and varied by race and sex (preventive fraction is a measure of the public health burden of disease).
“Preventive fraction tells us, hypothetically, what proportion of disease could be eliminated if the risk factor was removed from the population,” Carnethon said. One of the study’s important findings is the role of race and gender. Although a larger proportion of black participants and men develop hypertension over 20 years, fitness and physical activity play a similar role in the development of hypertension in black or white women and men, researchers said. “There’s no evidence from our study that activity or fitness recommendations for hypertension prevention should be different by sex or race,” Carnethon said, adding that clinical trials should test activity prescriptions in all adults.The study’s primary limitation is that it cannot lead to a recommendation about the amount of physical activity needed to improve fitness and to lower the risk of developing hypertension, Carnethon said. So clinical trials are needed to manipulate activity and fitness.“In an observational study, we cannot specifically address whether high activity and fitness can actually prevent hypertension,” she said. “We can only discuss the associations of health behaviors and physical traits, i.e., fitness and hypertension development.”Co-authors are: Natalie Evans, M.D.; Timothy Church, M.D., M.P.H., Ph.D.; Cora Lewis, M.D.; Pamela Schreiner, Ph.D.; David Jacobs, Jr., Ph.D.; Barbara Sternfeld, Ph.D.; and Stephen Sidney, M.D., M.P.H.The National Heart, Lung, and Blood Institute funded the study.
Journal of the American Heart Association