Physically Active Avoid Hypertension, But Only if Fitness Is High

June 08, 2010

June 8, 2010 (Chicago, Illinois) — A new analysis of the longitudinal Coronary Artery Risk Development in Young Adults (CARDIA) study, published online June 1, 2010 in Hypertension, shows that both physical fitness and physical activity are inversely associated with the development of hypertension over a period of 20 years [1]. But importantly, the researchers illustrate that activity was significantly associated with nonhypertensive blood-pressure readings only when fitness levels were the highest.

The study is one of the few to jointly measure fitness and activity, and distinguishing between the two is important, they explain, because physical activity is a behavior, whereas aerobic fitness is a physiologic measure.

"We know that activity is the principal behavioral determinant of fitness, and we know that being more physically active can improve one's fitness. But the activity needs to be moderate to vigorous to adequately improve fitness to see the greater health benefits," lead author Dr Mercedes R Carnethon (Feinberg School of Medicine, Chicago, IL) told heartwire . While she concedes that this may not be rocket science, she says: "We are showing this, for the first time, with objective data, and it's good that this is consistent with what we know."

People should adopt good habits early on.

Also, the measurements were taken in young adulthood "and showed that even at a time when most young people are not that worried about their heart-disease risk factors and hypertension, it's important to adopt a physically active lifestyle," Carnethon says. Activity and fitness matter because activity behaviors tend to track over time, and this work shows that activity and fitness count in relation to the long-term development of heart disease. "So people should adopt good habits early on," she observes.

Hypertension Could Be Avoided if People Improved Their Fitness

Carnethon et al tested whether fitness and activity were independently associated with the 20-year incidence of hypertension in 4618 men and women aged 18 to 30 initially, who were participating in the CARDIA study.

At baseline, fitness was estimated based on the duration of a symptom-limited graded exercise treadmill test, and physical activity was self-reported.

The incidence rate of hypertension--systolic BP >140 mm Hg or diastolic BP >90 mm Hg--was 13.8 per 1000 person-years (n=1022). Both baseline fitness (hazard ratio 0.63) and physical activity (hazard ratio 0.86) were inversely associated with incident hypertension when included jointly in a model that also adjusted for age, sex, race, smoking status, systolic BP, alcohol intake, HDL cholesterol, dietary fiber, dietary sodium, fasting glucose, and body-mass index.

A previous analysis of the same study showed that the young adults who were the most physically active had a decreased risk of developing hypertension, the researchers note.

"We extend beyond the previous analysis to demonstrate a significant inverse association of fitness . . . with incident hypertension," they say, and the additional five years of follow-up in this new report, with 388 more hypertension events, enabled them to stratify their analysis by activity categories.

The magnitude of association between physical activity and hypertension was strongest among participants in the high-fitness category (hazard ratio 0.80), whereas the strength of association between fitness and hypertension was similar across tertiles of activity.

Fitness, says Carnethon, is a trait that reflects a combination of activity behaviors, genetic potential, and functional health of various organ systems. A third of hypertension cases (34%) could be prevented if participants moved to a higher fitness category; this figure varied by race and sex, however.

But this being an observational study, the researchers were unable to make a recommendation for the amount of activity needed to improve fitness levels to a higher category, Carnethon noted. Clinical trials will be needed to determine this, she added.

She said also that while the rates of hypertension were much higher among black participants in the study, the association of activity and fitness with hypertension was similar in both blacks and whites. "So it is very important to promote activity and fitness in all racial groups," she concluded.

The authors declare that they have no conflicts of interest.