Body mass index and incident hospitalisation for cardiovascular disease in 158 546 participants from the 45 and Up Study

Abstract

Objective: To investigate the relationship between fine gradations in body mass index (BMI) and risk of hospitalisation for different types of cardiovascular disease (CVD).

Design, subjects and methods: The 45 and Up Study is a large-scale Australian cohort study initiated in 2006. Self-reported data from 158 546 individuals with no history of CVD were linked prospectively to hospitalisation and mortality data. Hazard ratios (HRs) of incident hospitalisation for specific CVD diagnoses in relation to baseline BMI categories were estimated using Cox regression, adjusting for age, sex, region of residence, income, education, smoking, alcohol intake and health insurance status.

Results: There were 9594 incident CVD admissions over 583 100 person-years among people with BMI≥20 kg m(-2), including 3096 for ischaemic heart disease (IHD), 1373 for stroke, 411 for peripheral vascular disease (PVD) and 320 for heart failure. The adjusted HR of hospitalisation for all CVD diagnoses combined increased significantly with increasing BMI (P(trend) <0.0001)). The HR of IHD hospitalisation increased by 23% (95% confidence interval (95% CI): 18-27%) per 5 kg m(-2) increase in BMI (compared to BMI 20.0-22.49 kg m(-2), HR (95% CI) for BMI categories were: 22.5-24.99=1.25 (1.08-1.44); 25-27.49=1.43 (1.24-1.65); 27.5-29.99=1.64 (1.42-1.90); 30-32.49=1.63 (1.39-1.91) and 32.5-50=2.10 (1.79-2.45)). The risk of hospitalisation for heart failure showed a significant, but nonlinear, increase with increasing BMI. No significant increase was seen with above-normal BMI for stroke or PVD. For other specific classifications of CVD, HRs of hospitalisation increased significantly with increasing BMI for: hypertension; angina; acute myocardial infarction; chronic IHD; pulmonary embolism; non-rheumatic aortic valve disorders; atrioventricular and left bundle-branch block; atrial fibrillation and flutter; aortic aneurysm; and phlebitis and thrombophlebitis.

Conclusion: The risk of hospitalisation for a wide range of CVD subtypes increases with relatively fine increments in BMI. Obesity prevention strategies are likely to benefit from focusing on bringing down the mean BMI at the population level, in addition to targeting those with a high BMI.

Figure 1

Age standardised rates per 1000 person-years of all CVD and cause-specific CVD hospitalisation since baseline by BMI categories and sex, directly age-adjusted to 2006 New South Wales population. BMI, body mass index; CVD, cardiovascular disease.

Figure 2

Relative risks (95% CI) of CVD admission since baseline, according to BMI categories. Crude rates are per 1000 person-years. HR* adjusted for age and sex only. HR^# adjusted for age, sex, region of residence, household income, education, smoking, alcohol intake and health insurance. HR^#s are plotted on a log scale at median BMI for the categories and are represented with squares with areas inversely proportional to the variance of the logarithm of the HR, providing an indication of the amount of statistical information available; 95% CIs are indicated by vertical lines. BMI, body mass index; CI, confidence intervals; CVD, cardiovascular disease; HR, hazards ratios.

Figure 3

Relative risks (95% CI) of hospital admission for ischaemic heart disease in subgroups of (a) diabetes status and (b) physical functioning at baseline, according to BMI categories. Level of physical functioning is based on Medical Outcomes Score—Physical Functioning; <75 (lower functioning) or ⩾75 (higher functioning). *Reference group for HR. HR adjusted for age, sex, region of residence, household income, education, smoking, alcohol intake and health insurance. HRs are plotted on a log scale at median BMI for the categories and are represented with squares with areas inversely proportional to the variance of the logarithm of the HR, providing an indication of the amount of statistical information available; 95% CIs are indicated by vertical lines. BMI, body mass index; CI, confidence intervals; HR, hazards ratios; p-years, person years.

Figure 4

Relative risk of IHD admission since baseline associated with 5 kg m⁻² increase in BMI among those with BMI ⩾20 kg m⁻² (n=151  751), in a range of population subgroups. Crude rates are per 1000 person-years. HR* adjusted for age and sex only. HR^# adjusted for age, sex, region of residence, household income, education, smoking, alcohol intake and health insurance. HRs are plotted on a log scale and are represented with squares with areas inversely proportional to the variance of the logarithm of the HR, providing an indication of the amount of statistical information available; 95% CIs are indicated by horizontal lines. PA sessions per week: number of physical activity session per week, weighted for intensity. Health insurance includes private health insurance or Department of Veterans Affairs health card. CI, confidence intervals; HR, hazards ratios; MOS-PF, Medical Outcomes Score—Physical Functioning; p-years, person years.