Background: In Switzerland, socio-demographic and behavioural factors are associated with obesity, but no study ever assessed their impact on weight gain using prospective data.
Methods: Data from 4,469 participants (53.0% women), aged 35 to 75 years at baseline and followed for 5.5 years. Weight gain was considered as a rate (kg/year) or as gaining ≥5 kg during the study period.
Results: Rate of weight gain was lower among participants who were older (mean ± standard deviation: 0.46 ± 0.92, 0.33 ± 0.88, 0.21 ± 0.86 and 0.06 ± 0.74 kg/year in participants aged [35-45], [45-55], [55-65] and [65+] years, respectively, P<0.001); physically active (0.27 ± 0.82 vs. 0.35 ± 0.95 kg/year for sedentary, P < 0.005) or living in couple (0.29 ± 0.84 vs. 0.35 ± 0.96 kg/year for living single, P < 0.05), and higher among current smokers (0.41 ± 0.97, 0.26 ± 0.84 and 0.29±0.85 kg/year for current, former and never smokers, respectively, p<0.001). These findings were further confirmed by multivariable analysis. Multivariable logistic regression showed that receiving social help, being a current smoker or obese increased the likelihood of gaining ≥5 Kg: Odds ratio (OR) and 95% confidence interval (CI) 1.43 (1.16-1.77); 1.63 (1.35-1.95) and 1.95 (1.57-2.43), respectively, while living in couple or being physically active decreased the risk: 0.73 (0.62-0.86) and 0.72 (0.62-0.83), respectively. No association was found between weight gain and gender, being born in Switzerland or education.
Conclusions: In Switzerland, financial difficulties (indicated by receiving social help) and current smoking were associated with increases in body weight over a 5 years follow-up. Living in couple, being older or physically active were protective against weight gain.