Interactive Effects of Physical Fitness and Body Mass Index on the Risk of Hypertension

IMPORTANCE High body mass index (BMI) and low physical fitness are risk factors for hypertension, but their interactive effects are unknown. Elucidation of interactions between these modifiable risk factors may help inform more effective interventions in susceptible subgroups. OBJECTIVE To determine the interactive effects of BMI and physical fitness on the risk of hypertension in a large national cohort. DESIGN, SETTING, AND PARTICIPANTS This cohort study included all 1 547 189 military conscripts in Sweden from January 1, 1969, through December 31, 1997 (97%-98% of all 18-year-old men nationwide each year), who were followed up through December 31, 2012 (maximum age, 62 years). Data analysis was conducted August 1 through August 15, 2015. EXPOSURES Standardized aerobic capacity, muscular strength, and BMI measurements obtained at a military conscription examination. MAIN OUTCOMES AND MEASURES Hypertension identified from outpatient and inpatient diagnoses. RESULTS A total of 93 035 men (6.0%) were diagnosed with hypertension in 39.7 million person-years of follow-up. High BMI and low aerobic capacity (but not muscular strength) were associated with increased risk of hypertension, independent of family history and socioeconomic factors (BMI, overweight or obese vs normal: incidence rate ratio, 2.51; 95% CI, 2.46-2.55; P < .001; aerobic capacity, lowest vs highest tertile: incidence rate ratio, 1.50; 95% CI, 1.47-1.54; P < .001). Aerobic capacity was inversely associated with hypertension across its full distribution (incidence rate ratio per 100W, 0.70; 95% CI, 0.69-0.71; P < .001). A combination of high BMI (overweight or obese vs normal) and low aerobic capacity (lowest vs highest tertile) was associated with the highest risk of hypertension (incidence rate ratio, 3.53; 95% CI, 3.41-3.66; P < .001) and had a negative additive and multiplicative interaction (P < .001). Although high BMI was a significant risk factor for hypertension, low aerobic capacity also was a significant risk factor among those with normal BMI. CONCLUSIONS AND RELEVANCE In this large national cohort study, high BMI and low aerobic capacity in late adolescence were associated with higher risk of hypertension in adulthood. If confirmed, our findings suggest that interventions to prevent hypertension should begin early in life and include not only weight control but aerobic fitness, even among persons with normal BMI.