Trends in body mass index and blood pressure associations from 1989 to 2018: co-ordinated analysis of 145,399 participants

BackgroundHigh body mass index (BMI) is an important contributor to higher blood pressure (BP) levels and its deleterious consequences. However, the strength of this association may be context-specific and differ across time due to increases in medication use or secular changes in body composition. Thus, we utilised two independent data sources to investigate if associations between BMI and systolic BP (SBP) in Britain changed from 1989-2018. MethodsWe used 23 repeated cross-sectional datasets--the Health Survey for England (HSE) at [≥]25 years (1994-2018; N=126,742); and three British birth cohorts (born 1946, 1958, and 1970) with outcomes available at 43-46 years (N=18,657). Anthropometry and BP were measured using standard protocols. We used linear and quantile regression to investigate cross-sectional associations between BMI and SBP. ResultsIn HSE, associations were weaker in subsequent years, and this trend was most pronounced amongst older adults--after accounting for sex, treatment and education, the mean difference in SBP per 1 kg/m2 increase in BMI amongst adults [≥]55 years was 0.75mmHg (95% CI: 0.60, 0.90) in 1994, 0.66mmHg (0.46, 0.85) in 2003, and 0.53mmHg (0.35, 0.71) in 2018. In cohorts, BMI and SBP associations were of similar magnitude in 1958 and 1970 cohorts and weaker in the 1946 cohort. Quantile regression analyses suggested that associations between BMI and SBP were present both below and above the hypertension threshold. ConclusionThe consequences of BMI may differ across time and by age --associations between BMI and SBP appear to have weakened in recent decades, particularly in older ages. Thus, at older ages, this weakening strength of association may partly offset the public health impacts of increases in obesity prevalence. However, BMI remains positively associated with SBP in all adult age groups, highlighting the potential adverse consequences of the ongoing obesity epidemic.