Does blood pressure inevitably rise with age?: longitudinal evidence among forager-horticulturalists

Abstract

The rise in blood pressure with age is a major risk factor for cardiovascular and renal disease, stroke, and type 2 diabetes mellitus. Age-related increases in blood pressure have been observed in almost every population, except among hunter-gatherers, farmers, and pastoralists. Here we tested for age-related increases in blood pressure among Tsimane forager-farmers. We also test whether lifestyle changes associated with modernization lead to higher blood pressure and a greater rate of age-related increase in blood pressure. We measured blood pressure longitudinally on 2248 adults age ≥ 20 years (n=6468 observations over 8 years). Prevalence of hypertension was 3.9% for women and 5.2% for men, although diagnosis of persistent hypertension based on multiple observations reduced prevalence to 2.9% for both sexes. Mixed-effects models revealed systolic, diastolic, and pulse blood pressure increases of 2.86 (P<0.001), 0.95 (P<0.001), and 1.95 mmHg (P<0.001) per decade for women and 0.91 (P<0.001), 0.93 (P<0.001), and -0.02 mmHg (P=0.93) for men, substantially lower than rates found elsewhere. Lifestyle factors, such as smoking and Spanish fluency, had minimal effect on mean blood pressure and no effect on age-related increases in blood pressure. Greater town proximity was associated with a lower age-related increase in pulse pressure. Effects of modernization were, therefore, deemed minimal among Tsimane, in light of their lean physique, active lifestyle, and protective diet.

Figure 1

Prevalence of hypertension by age and sex among those sampled at least twice.

Figure 2

BP by age and sex. Generalized additive models of SBP, DBP and PP for males (solid lines) and females (dashed lines), controlling for BMI and pregnancy status. Tsimane models are mixed models to control for repeated observations (n=5,528 observations, 1,749 individuals). NHANES models are based on a single time-point (n=7,359). Both models are illustrated at BMI=25.84, which is the midpoint between mean BMI for Tsimane (23.67) and NHANES (28.00). Gray lines are 95% confidence intervals for the mean.

Figure 3

Change in SBP (A, B), DBP (C, D) and PP (E, F) per decade by sex and age. Points are ΔBP versus mean observation age (Table 2, Step 1). Lines are spline fits and 95% confidence intervals for the slopes as a function of mean observation age, estimated with a generalized additive model (Table 2, Step 2).

Figure 4

Distribution of individual ΔSBP (A), ΔDBP (B) and ΔPP (C) per decade by sex and age. Females are shown on the left (gray) and males on the right (white). Only individuals with two or more measures and at least five years between their earliest and latest BP measures were included. Boxplots show the first to third quartile range. Distributions are smoothed density plots. White circles indicate medians.

Figure 5

Increase in (a) SBP and (b) DBP per decade. Cross-cultural sample includes 52 populations from the INTERSALT study (ages 20–59). Tsimane slope estimates are represented by black dots. Other populations inside ovals include the Brazilian Yanomamo and Xingu Amerindians, Papua New Guinea highlanders and Kenyans.