Factors Associated with High Weight Gain and Obesity Duration: The Norwegian Women and Cancer (NOWAC) Study

Aim: To identify factors associated with high weight gain and obesity duration in a representative sample of Norwegian women. Methods: 66,618 Norwegian women aged 34-70 years at baseline were included in the analysis. Baseline and follow-up questionnaires completed in 1991-2011 provided information on height, weight as well as sociodemographic, lifestyle and reproductive factors. We assessed the association with multivariable logistic regression. Results: Women gained on average 0.5 kg/year (95% CI 0.5-0.5 kg/year) during 6 years of follow-up, and 3.5% maintained in obesity during 13 years of follow-up. The factors with strongest association with high weight gain (≥10 kg) were smoking cessation (cessation vs. no change, OR = 4.39, 95% CI 3.91-4.94) and decreased physical activity level (decrease vs. no change, OR = 2.40, 95% CI 2.21-2.61). Low physical activity level (high vs. low, OR = 0.17, 95% CI 0.14-0.20), higher than median age at menarche (over median vs. median or under median, OR = 0.36, 95% CI 0.31-0.41), and less than 10 years of education (>12 years vs. <10 years, OR = 0.44, 95% CI 0.37-0.51) were strongly associated with obesity duration. Conclusion: The modifiable factor with the strongest association with adverse weight development and potential for prevention was low or decreased physical activity level.