Is the obesity epidemic reversing favorable trends in blood pressure? Evidence from cohorts born between 1890 and 1990 in the United States

Abstract

Background

Previous reports have described favorable changes in the relationship between systolic blood pressure and age in recent birth cohorts. The obesity epidemic might threaten that pattern.

Objectives

To update analyses of differences between birth cohorts in the relationship between systolic blood pressure and age and to determine whether increases in obesity have had adverse effects.

Methods

We examined the systolic blood pressure distributions across birth cohorts born between 1890 and 1990 in 68,070 participants, aged 18–74 years, in the National Health (and Nutrition) Examination Surveys between 1960 and 2008. We postulated that age-adjusted 10th, 25th, 50th, 75th, and 90th percentiles of systolic blood pressure had decreased in more recent versus earlier cohorts, and that this pattern had slowed or reversed recently due, at least in part, to obesity.

Results

After adjusting for gender, race, age and age², the 10th, 25th, 50th, 75th, and 90th percentiles of systolic blood pressure were 1.1, 1.4, 1.9, 2.5, and 3.4 mmHg lower for each decade more recently born (all P < .0001). Quadratic terms for birth cohort were positive and significant (P < .001) across all percentiles, consistent with a decelerating cohort effect. Mediation of this deceleration was observed for body mass index ranging from 20.4% to 44.3% (P < .01 at all percentiles).

Conclusions

More recent cohorts born in the United States between 1890 and 1990 have had smaller increases in systolic blood pressure with aging. At any age, their systolic blood pressure distributions are shifted lower relative to earlier cohorts. Decreases of 1.9 mmHg in the median systolic blood pressure per decade translates into 11.4–13.3 mmHg over 6–7 decades, a shift that would contribute importantly to lower rates of cardiovascular diseases. These favorable changes are slowing, perhaps owing, at least in part, to the obesity epidemic.

Introduction

Previously, we have demonstrated that the increase in systolic blood pressure frequently observed with aging was becoming less notable in more recent birth cohorts in the United States over the past 50 years or longer, and that this pattern was present across the entire distribution of systolic blood pressure, including the 10th, 50th and 90th percentiles [1]. That evidence, based on date from the National Health Examination Survey (NHES), and the National Health and Nutrition Examination Surveys (NHANES) I–III, was replicated by Tunstall-Pedoe et al [2], who demonstrated declining blood pressure levels over a 10-year period in multiple populations that were studied in the Multinational Monitoring of trends and determinants in Cardiovascular disease project. Both reports demonstrated shifts in the systolic blood pressure distributions across the entire range of systolic blood pressure, patterns that could not be explained by improved treatment of persons with high blood pressure that would only affect those participants with higher blood pressure levels [1], [2]. These findings were surprising, given the ongoing epidemic of obesity and the established association between obesity and high blood pressure [3]. Our previous results supported the conclusion that the obesity epidemic was blunting the trend toward lower systolic blood pressure levels in more recent birth cohorts [1]. The forces underlying the flattening of the slope of blood pressure with age remain unknown; further research to identify these influences might support prevention efforts.

Since our previous publication, limited to data available through 1994, the obesity epidemic has continued to worsen in the United States [4], [5], [6], [7], [8], and an increased prevalence of high blood pressure has been reported in the United States, based on analyses of the more recent national surveys as repeated cross-sectional assessments [9]. In this report, we update our previous assessment of changes in the pattern of blood pressure development with aging to address several questions with data available through 2008. Is there evidence of a birth cohort effect, that is, a relative flattening of the slope of systolic blood pressure percentiles with age in more recent birth cohorts? Does this effect accumulate with age; that is, are the birth cohort differences in systolic blood pressure greater at older ages than at younger ages? Is there evidence of deceleration or reversal of this pattern across the most recent birth cohorts that have been most influenced by the obesity epidemic? If there is evidence of a recent deceleration or reversal of the birth cohort changes, does obesity (body mass index [BMI]) mediate that deceleration?