Body mass index is a longitudinal risk factor for hypertension
Image: PD
Key Study Points:
- Obesity during young adulthood increases an individual’s lifetime risk for developing hypertension independent of other risk factors including smoking, physical activity, and coffee or alcohol consumption.
- The rate of change of BMI has a dose dependent effect on the risk of incident hypertension.
Primer: Hypertension is the most common reason cited for a visit to the physician’s office and the most frequent indication written for the prescription of medications in the United States. Nearly one third of adults in the United States suffer from this condition and it is estimated that as the rates of overweight and obesity continue to rise in the population, the proportion of individuals suffering from hypertension will increase concomitantly.
Obesity is a major modifiable risk factor for hypertension. Studies have shown that individuals with central adiposity are at the greatest risk for developing hypertension in addition to other metabolic derangements such as insulin resistance and lipid abnormalities. Indeed, it has been suggested in recent research that the pathogenesis of hypertension in obesity may attributed to an initial increase in cardiac output which is then maintained due to an increase in total systemic vascular resistance. Further, observational studies have shown that weight reduction may have a beneficial effect on hypertension. However, there remains little long-term data regarding the relationship between obesity and hypertension throughout the lifetime. By employing an extended follow up interval, the authors of this study aimed to elucidate the relationship between obesity and the risk it confers on the development of hypertension at various points during the lifespan.
Background Reading:
- Obesity and weight reduction in hypertension [UpToDate]
- The INTERSALT study: relations of body mass index to blood pressure [J Hum Hypertens]
- Weight and blood pressure. Findings in hypertension screening of 1 million Americans [JAMA]
This [prospective cohort] study: 1132 white male medical students were studied for a median follow up of 46 years. BMI and blood pressure were assessed during medical school to establish a baseline and were thereafter followed by annual questionnaires.
Data analysis revealed that men who were obese at baseline experienced a four times greater risk of developing hypertension compared to their normal weight counterparts (HR = 4.17, CI: 2.34-7.42) even after adjusting for other factors, including smoking, coffee and alcohol intake, physical activity, parental premature hypertension and baseline BMI. Compared to men with normal BMI at both age 25 and 45, men who were normal at 25 but became overweight/obese at 45 had a higher risk for hypertension (HR = 1.57, CI: 1.20-2.07); and men who were overweight/obese at both 25 and 45 were at an even higher risk (HR = 1.91, CI: 1.46-2.49). Finally, the authors demonstrated a dose response relationship between BMI and hypertension, with every 1 kg/m2 increase in BMI associated with an increased risk of incident hypertension at a hazard ratio of 1.06 (CI: 1.04-1.08).
In sum: The authors demonstrated that obesity in men during early and mid adulthood confers a significant risk of developing hypertension over the lifetime, with longer duration of obesity associated with higher risk of hypertension. However, this study faces several limitations. First, the study focused on a select population consisting of only white males in relatively high socioeconomic standing, thus reducing its generalizability. Second, body weight, hypertension diagnosis and presence of modifiable risk factors were assessed via survey, thus the results of the study may have been affected by reporting bias on part of the participants. Finally, dietary factors were not analyzed. Diet is an essential component of general health and a poor diet has been linked to the development of both obesity and hypertension. Thus, it is possible that dietary factors may have been a confounder that could potentially explain the relationship between BMI and hypertension.
Click to read study in Circulation
By [DM] and [MK]
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