High BMI, Poor Fitness Independently Predict Midlife Hypertension

Pam Harrison

January 22, 2016

CHICAGO, IL — A high body-mass index (BMI) and poor aerobic capacity in late adolescence are both independently associated with a higher risk of developing hypertension in middle age, and their effects are additive, suggests a study based on a large Swedish male cohort[1].

Among the findings: the young male participants with normal baseline BMI but poor fitness still had a sharply and significantly increased risk of hypertension later in life.

"This was our most surprising finding, and it suggests that interventions to prevent hypertension should include not only weight control but aerobic fitness, even among people with normal BMI," lead author Dr Casey Crump (Mount Sinai School of Medicine, New York, NY) said to heartwire from Medscape in an email.

Crump is lead author on the longitudinal study of 1.5 million men conscripted for Sweden's military at age 18, which was published January 19, 2016 in JAMA Internal Medicine. He was at Stanford University (Palo Alto, CA) when the study was conducted. "To our knowledge," he said, "this is the first study to examine the combined effects of high BMI and low fitness in late adolescence on the long-term risk of hypertension in adulthood."

Independent and Additive Risk

Over the cohort's mean follow-up of 27.5 years, 6% received a new diagnosis of hypertension at a mean age of 49.8 years. Their mean baseline BMI was 21.1 kg/m2, statistically similar to the median of 21.1 kg/m2 in those who didn't go on to receive a hypertension diagnosis, the authors report.

After adjustment for family history, socioeconomic factors, and other potential confounders, participants who at baseline were overweight or obese (in the ≥85th percentile on the Center for Disease Control and Prevention's 2000 growth chart of BMI for gender and age) were 2.5-fold more likely to be diagnosed with hypertension in middle age compared with those with normal BMI (P<0.001).

After adjustment for BMI and other potential confounders, a low aerobic capacity was also significantly associated with a 50% increased risk of having high blood pressure in middle age for men in the lowest aerobic tertile compared with those in the highest (P<0.001).

The combination of having low aerobic capacity and being overweight or obese increased the risk of hypertension about 3.5 times compared with those with a high aerobic capacity and normal BMI (P<0.001). Even among men with normal BMI, low aerobic capacity was associated with a 62% greater likelihood of being hypertensive in middle age (P<0.001).

"Aerobic fitness early in life has long-term health benefits even among those who are not overweight or obese," Crump observed. But in contrast, the report notes, muscle strength had little effect on the risk of developing hypertension in middle age, regardless of BMI in late adolescence.

Search for Common Denominators

As aerobic or cardiorespiratory fitness (CRF) and obesity are both major risk factors for cardiovascular disease, it's important to identify their common denominators, observes an editorial, with lead author Dr Carol Lavie (Ochsner Medical Center, New Orleans, LA)[2]. "A main factor is physical activity," it states, and "the strongest predictor of CRF is physical activity or levels of exercise training."

Lavie and colleagues contend that "substantial" efforts are needed to increase levels of physical activity across all ages to improve fitness levels and prevent obesity. "We agree with Crump et al that efforts to prevent hypertension need to be started early by preventing weight gain and improving levels of CRF in children and adolescents," they write.

"As physicians, it is imperative that we document levels of physical activity during almost all patient encounters and that we use this opportunity at nearly ever visit to promote and prescribe physical activity to all of our patients."

The study's authors had no relevant financial relationships. Lavie reports being the author of The Obesity Paradox and serving as a lecturer for Coca-Cola; disclosures for the other editorialists are listed in the article.

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