Physical Activity and the Incidence of Obesity in Young African-American Women

BackgroundObesity occurs more commonly among African-American women than among other racial/ethnic groups, and most weight gain occurs before middle age.PurposeThe study prospectively investigated the relationship of vigorous exercise and brisk walking to the incidence of obesity (BMI ≥30) among African-American women aged <40 years.MethodsDuring 1995–2009 in the Black Women’s Health Study, the current authors followed 20,259 African-American women who were aged <40 years and not obese at baseline. BMI, exercise, and walking were assessed at baseline and on biennial follow-up questionnaires. Data for BMI were collected through 2009. Data for exercise and walking were collected through 2007. Validation and reproducibility data indicated that reporting was more accurate for vigorous exercise than for brisk walking. Cox proportional hazards models estimated incidence rate ratios (IRRs) and 95% CIs of incident obesity for hours/week of vigorous exercise and walking relative to “little or no exercise” (<1 hour/week of vigorous exercise and <1 hour/week of brisk walking). The analyses were conducted in 2012.ResultsThe incidence of obesity decreased with increasing vigorous exercise; the IRR was 0.77 (95% CI=0.69, 0.85) for ≥7 hours/week relative to little or no exercise; the IRRs were reduced both among women with a healthy weight (BMI <25) at baseline and among women who were overweight (BMI 25–<30) at baseline. The IRRs for brisk walking for exercise and walking for transport were <1.0 for most levels of walking, but without clear trends of decreasing risk with increasing time spent walking.ConclusionsThe results suggest that vigorous exercise may reduce the incidence of obesity among young African-American women. Results for brisk walking were inconclusive.