Exploring secular changes in the association between BMI and waist circumference in Mexican-origin and white women: a comparison of Mexico and the United States.

OBJECTIVES: BMI and waist circumference (WC) tend to be highly correlated, but changes in lifestyle behaviors may promote greater accumulation of abdominal fat for the same BMI in recent years. We examined secular shifts in BMI and WC distributions, and investigated whether WC for a given BMI has changed over time among Mexican-origin women in Mexico and the US, and in US white women as a comparison.
METHODS: Nationally representative surveys for women aged 20-49 years from Mexico (1988, 1999, and 2012) (n = 37,116) and the US (1988-1994, 1999-2002, and 2007-2010) (n = 6,985) were used. Quantile regressions estimated age-adjusted changes in BMI and WC across years; linear regression tested changes in mean WC over time, adjusting for age and BMI.
RESULTS: In all women, BMI and WC at most centiles increased over time. WC was also significantly higher over time for the same BMI, though the increase was largest in Mexican women. For example, WC was 6.7 cm (standard error (SE): 0.17, P < 0.0001) higher in 2012 than in 1999 among Mexican women, holding age and BMI constant. Estimates were smaller in magnitude for Mexican-American and white women (∼3 cm, P < 0.01), even when comparing over a longer timeframe (1988-1994 to 2007-2010). In all groups, WC adjusted for BMI increased to a larger extent among younger cohorts.
CONCLUSION: WC for the same BMI has increased in Mexican-American, white, and Mexican women of reproductive age. These patterns may have implications for future cardio-metabolic burden in Mexico and the US.