Changes in the body mass index and blood pressure association across time: Evidence from multiple cross-sectional and cohort studies

Abstract

Although body mass index (BMI) is considered a key determinant of high blood pressure, its importance may differ over time and by age group. We utilised separate data sources to investigate temporal changes in this association: 23 independent (newly sampled), repeated cross-sectional studies (Health Survey for England (HSE)) at ≥25 years (1994-2018; N = 126,742); and three British birth cohorts at 43-46 years (born 1946, 1958, and 1970; N = 18,657). In HSE, associations were weaker in more recent years, with this trend most pronounced amongst older adults. After adjustment for sex, anti-hypertensive treatment and education, the mean difference in systolic blood pressure (SBP) per 1 kg/m² increase in BMI amongst adults ≥55 years was 0.75 mmHg (95%CI: 0.60-0.90) in 1994, 0.66 mmHg (0.46-0.85) in 2003, and 0.53 mmHg (0.35-0.71) in 2018. In the 1958 and 1970 cohorts, BMI and SBP associations were of similar magnitude yet weaker in the 1946 cohort, potentially due to differences in blood pressure measurement device. Quantile regression analyses suggested that associations between BMI and SBP were present both below and above the hypertension threshold. A weaker association between BMI and blood pressure may partly offset the public health impacts of increasing obesity prevalence. However, despite sizable increases in use of antihypertensive medication, BMI remains positively associated with SBP in all ages. Our findings highlight the need to tackle non-medical factors such as population diet which influence both BMI and blood pressure, and the utility of using multiple datasets to obtain robust inferences on trends in risk factor-outcome associations across time.

Keywords: Blood pressure; Body mass index; Hypertension; Obesity; Trends.

Fig. 1

Associations between body mass index (kg/m²) and systolic blood pressure (mmHg) across adulthood (≥25 years, from independent, repeated cross-sectional English data, left panel; N = 126,742), and midlife (43–46 years, from British birth cohort data, right panel; N = 18,657). Note: raw SBP values adjusted for use of antihypertensive medication (by adding a constant of 10 mmHg for those using antihypertensive medication). HSE models are adjusted for sex, age, and education. Cohort models are also adjusted for mother's education and cohort member's own education, social class at birth, and social class in midlife. Sample sizes in each cohort / survey year shown in Supplementary Figs. 1 and 2, respectively.

Fig. 2

Associations between body mass index (kg/m²) and systolic blood pressure (mmHg) in 25–54 years (left panel) and 55+ years (right panel, from independent, repeated cross-sectional English data; N = 126,742). Note: SBP values adjusted for use of antihypertensive medication (by adding a constant of 10 mmHg for those using antihypertensive medication). Models are also adjusted for sex, age, and education. Sample sizes in each survey year are shown in Supplementary Fig. 2.

Fig. 3

Associations between body mass index and systolic blood pressure quantiles (mmHg) across adulthood (≥25 years, from repeated cross-sectional data, left panel; N = 126,742), and midlife (43–46 years, from birth cohort data, right panel; N = 18,657). Estimates show the difference in SBP per 1 unit increase in BMI at specified centiles of the SBP distribution; for example, Q50 shows the difference at the median. Note: raw SBP values adjusted for use of antihypertensive medication (by adding a constant of 10 mmHg for those using antihypertensive medication); estimates are adjusted for sex and education attainment.