Baseline characteristics are presented in . Blood pressure, treadmill test duration and activity levels varied across race and sex groups. Black women had higher systolic and diastolic blood pressure than white women, whereas only systolic blood pressure was significantly higher in black versus white men. Activity and fitness were lower in black and white women as compared with men. shows the proportion of study participants with a given level of fitness within activity categories. The proportion of participants with low fitness was smaller with higher activity levels among all participants; the inverse was true for high fitness. These patterns were more pronounced in white participants than black participants and a greater proportion of white participants had high fitness as compared with black participants.
Baseline Characteristics* of Study Population by Gender and Ethnicity
Proportion of participants by sex-specific fitness categories and activity tertiles, by race-sex
Over 20 years, 1022 participants developed hypertension at a rate of 13.8 per 1000 person-years. One-third (n= 340) of participants with incident hypertension had high blood pressure but did not use medications; 451 participants were identified based on antihypertension medications but blood pressure was not elevated (44.1%) and 231 participants had a combination of high blood pressure and medications (22.6%). The rate of hypertension was 20.7, 19.6, 10.6, and 6.1 in black women, black men, white men and white women, respectively. Across race-sex groups, there was an inverse, graded association between fitness category and the development of hypertension (). The incidence of hypertension was inversely associated with fitness category in all race and sex groups, though the absolute rates varied by sex (). By contrast, patterns of association between activity and incident hypertension were less pronounced. .
Hazard Ratios (95% Confidence Intervals) of the Association of Fitness or Activity* with Incident Hypertension in the full sample and within Activity and Fitness Categories
Incident rates, hazard ratios (95% Confidence Intervals) and Preventive Fraction* for the association of activity and fitness† with incident hypertension
Neither race nor sex modified the association between fitness and hypertension. Treadmill duration (per 2.9 minutes longer) and activity score (per 297 EU higher) were each inversely associated with incident hypertension (). The magnitude of association of both fitness and activity with incident hypertension was modestly attenuated but remained statistically significant following additional adjustment for covariates. There was no evidence of statistical interaction between activity and fitness in association with the development of hypertension (χ2=1.15, p=0.28). When both were included in the same model, fitness remained significantly and independently associated with a lower likelihood of developing hypertension while activity attenuated to non-significance. Our findings were robust as they were persisted with adjustment for family history, were present in the subset of participants who exercised to at least 85% of their age-predicted maximum heart rate, participants who did not experience hospitalized CVD during follow-up, and when incident hypertension was determined among those participants who had it at more than 1 follow-up examination.
Fitness was significantly and inversely associated with the development of hypertension within each tertile of physical activity. Despite the absence of an interaction between activity and fitness, activity was only significantly inversely associated with the development of hypertension in the highest category of fitness. There was no difference when fasting insulin was used in place of fasting glucose or waist circumference was used in place of BMI.
The HR for developing hypertension ranged from 0.54 to 0.79 per 1 category higher fitness measure across race and sex groups (). The proportion of hypertension that could theoretically be prevented was highest in white men and women but all race-sex groups demonstrated the potential for a lower hazard with higher fitness. Although baseline activity category was inversely associated with incident hypertension, the HR was only statistically significant in black men.