Overweight in midlife and risk of cancer in late life: A nationwide Swedish twin study.

Our study examined whether midlife overweight (body mass index [BMI] ≥25) is associated with late-life cancer risk and explored the role of genetic and early-life environmental factors in this association. The study included 14,766 individuals from the Swedish Twin Registry, whose midlife (30-50 years) height and weight were recorded. Information on cancer diagnoses in late life (>65 years) was derived from the National Patient Registry and Cancer Registry. Generalized estimating equation (GEE) models were used to analyze unmatched case-control data (controlled for the clustering of twins within a pair). A co-twin matched case-control analysis used conditional logistic regression to compare cancer-discordant twins. Of all participants, 3968 (26.9%) were overweight and 4253 (28.8%) had cancer. In multi-adjusted GEE models using normal-weight (BMI 18.5-24.9) participants as the reference group, overweight was related to higher risk of colon cancer (OR 1.36, 95% CI: 1.00-1.84, p = 0.049), liver cancer (OR 2.00, 95% CI: 1.11-3.62), cervix uteri cancer (OR 2.86, 95% CI: 1.19-6.91) and corpus uteri cancer (OR 1.78, 95% CI: 1.14-2.78) but lower risk of nonmelanoma skin cancer (OR 0.77, 95% CI: 0.66-0.90). In conditional logistic regression analysis, these associations were attenuated becoming nonsignificance. The difference in ORs from the unmatched and matched analyses was not significant. In conclusion, midlife overweight is associated with increased risk of late-life colon, liver and uterine cancer but reduced risk of late-life nonmelanoma skin cancer. Further investigations are warranted to explore the role of genetic and early-life environmental factors in these associations.