The Relationship Between Body Mass Index and Hypertension in Elderly Greeks: The Nemea Primary Care Study

To the Editor: Many epidemiological studies have found higher prevalence of hypertension in obese patients and a positive association between body mass index (BMI) and blood pressure (BP).1 This linear relationship between BMI and BP has been observed in young and middle-aged individuals. Subsequently, obesity and weight gain in young individuals are associated with greater cardiovascular mortality. Few data are available on the effect of obesity on cardiovascular morbidity in older patients. The association between coronary heart disease and obesity was not documented in Honolulu or in the Framingham Study, although in the Systolic Hypertension in the Elderly Program, low BMI was associated with greater cardiovascular morbidity and mortality.2,3 The aim of the current study was to determine the relationship between body weight and prevalence of hypertension in an older adult population. Six hundred fifteen subjects (70.2% men, 47.7% women) were included in the analysis. Mean age±standard deviation was 73.5±6.1. Mean BMI was 26.4±3.8 kg/m2; 69.2% of men and 63.7% of women had a BMI of 25.0 or higher. There were more overweight participants in all of the age categories. Mean BMI was significantly lower in the normotensive population aged 75 to 79. Most overweight subjects were aged 70 to 74. The overall prevalence of hypertension was 425 of 615 (69.1%, 95% confidence interval (CI)=66.5–71.6), 70.7% of men and 67.0% of women. Hypertension prevalence rates rose with age (from 63.5% in those aged 65-69 to 76.8% in those aged ≥80). In participants aged 65 to 69 and 70 to 74, the prevalence of hypertension was higher in patients with a BMI of 25.0 or higher (aged 65–69: 72.0% vs 48.3% in those with a BMI<25, P<.001; aged 70–74: 73.3%, vs 56.9% in those with a BMI<25, P=.03) but with no significant difference after the age of 74 (70.9%, vs 71.4% in those with a BMI<25) (Table 1). Although prevalence was higher in overweight participants, the trend was toward a greater rise in prevalence of hypertension with age in lean participants (and a decrease of hypertension prevalence in the overweight group especially after the age of 74) than in the overweight group (BMI<25 in 48.3% of those aged 65–69, 56.9% of those aged 70–74, 71.4% of those aged 75–79, and 72.3% of those aged ≥80; P<.001). The odds ratio (OR) of development of hypertension adjusted for age was 2.16 (95% CI=1.46–3.18) for persons with a BMI of 25.0 or higher. The OR for participants older than 75 was 1.19 (95% CI=0.63–2.25). In this study, prevalence of hypertension was higher in individuals with a BMI of 25.0 or higher and continued to increase with age. In many population-based surveys, BMI has been reported to correlate scientifically with systolic BP, diastolic BP, and hypertension prevalence,4 although the correlation between BP and BMI decreases significantly after the age of 60. An important finding of the current study was the greater risk for hypertension in individuals with a BMI of less than 25.0. Although hypertension prevalence was higher in overweight people than in those who were lean, the trend was toward a higher rise in prevalence with age in the lean group with statistical significance. This may be partly due to selective mortality of individuals with hypertension and partly due to reduction in BMI with age, whereas systolic BP rises for other reasons. Evidence from several genetic models suggests that obesity is not consistently associated with higher blood pressure.5,6 Although the relationship between hypertension, BMI, and age is complex, published analyses of data from the Third National Health and Nutrition Examination Survey (NHANES III) have presented interesting results supporting these findings.7 One study showed that the prevalence of hypertension at older ages, associated with higher BMI, is lower than at younger ages.8 The prevalence of hypertension in elderly men is high (50%) even in the normal range of BMI (BMI<25). Age of 60 and older was found to be the strongest risk factor for hypertension in both sexes after adjusting for BMI category. Thus, age could be a confounding factor in analyses of hypertension. A higher prevalence of hypertension in the lean than in the overweight group (OR=1.29, P=.03) was reported in an analysis of 3,600 participants in NHANES III.9 The exclusion of persons undergoing antihypertensive therapy raises a concern about possible bias in the assessment of the relationship between obesity and hypertension. From the same authors but in a different sample analysis, pulse pressure was lower with higher BMI. Several methodological problems of this study have to be considered. Sodium and potassium were not measured, physical activity was not assessed, and birth weight, as a risk factor for hypertension, was not recorded. These factors may influence BMI and hypertension and act as potential confounders. BMI, which was used as an indicator of adiposity, may be less sensitive in elderly people in whom abdominal adiposity is correlated with greater cardiovascular mortality even within the range of normal BMI values. Abdominal obesity in the current study was not evaluated through the waste to hip ratio, which is a stronger predictor of cardiovascular prognosis.10 Conflict of Interest: The editor in chief has reviewed the conflict of interest checklist provided by the author and has determined that none of the authors have any financial or any other kind of personal conflicts with this letter. Author Contributions: E. A. Skliros, P. Merkouris, and A. Sotiropoulos: concept and design, interpretation of data, and preparation of letter. M. Papasotiriou, C. Xipnitos, and Helen Liva: acquisition of subjects and data, and analysis and interpretation of data. Sponsor's Role: None.