Objective: To test the hypothesis that for any given body mass index (BMI) category, active individuals would have a smaller waist circumference than inactive individuals. Our second objective was to examine the respective contribution of waist circumference and physical inactivity on coronary heart disease (CHD) risk.
Design: Prospective, population-based study with an 11.4-year follow-up.
Subjects: A total of 21 729 men and women aged 45-79 years, residing in Norfolk, UK.
Methods: During follow-up, 2191 CHD events were recorded. Physical activity was evaluated using a validated lifestyle questionnaire that takes into account both leisure-time and work-related physical activity. Waist circumference was measured and BMI was calculated for each participant.
Results: For both men and women, we observed that within each BMI category (<25.0, 25-30 and >or=30.0 kg m(-2)), active participants had a lower waist circumference than inactive participants (P<0.001). In contrast, within each waist circumference tertile, BMI did not change across physical activity categories (except for women with an elevated waist circumference). Compared with active men with a low waist circumference, inactive men with an elevated waist circumference had a hazard ratio (HR) for future CHD of 1.74 (95% confidence interval (CI), 1.34-2.27) after adjusting for age, smoking, alcohol intake and parental history of CHD. In the same model and after further adjusting for hormone replacement therapy use, compared with active women with a low waist circumference, inactive women with an elevated waist circumference had an HR for future CHD of 4.00 (95% CI, 2.04-7.86).
Conclusion: In any BMI category, inactive participants were characterized by an increased waist circumference, a marker of abdominal adiposity, compared with active individuals. Physical inactivity and abdominal obesity were both independently associated with an increased risk of future CHD.