8Secular trend in body mass index in the adult population of three communities from the upper mid-western part of the USA: The Minnesota Heart Health Program

Secular trend in body mass index (BMI) over 7 years (1980-1987) was examined in the upper mid-western part of the USA using annual cross-sectional data collected by the Minnesota Heart Health Program. Significant secular increase in BMI adjusted for age and education was found in both men (0.08 kg/m²/year, P < 0.02) and women (0.19 kg/m²/year, P < 0.0001). In women, the secular increase occurred throughout the distribution of body weights but the change in the upper end was two to three times greater than that in the other parts of the distribution. In men, most of the increase in BMI occurred in the upper end of the distribution. Prevalence of obesity (defined as BMI ≥ 85th percentile at year 1: men, 30.16 kg/m²; women, 29.94 kg/m²) increased by 0.6 percent/year (P = 0.1) in men and by 1.0 percent/year (P = 0.002) in women. The results indicate that body weight is increasing in upper mid-western adults, probably largely as a result of already overweight individuals becoming more obese. The secular increase in BMI was not accompanied by systemic change in reported food intake and exercise, and could not be explained by decreased prevalence of smoking. Large increases in body weight, especially among those who are already overweight, may have a significant public health impact.