Lifestyle changes and risk of cancer: experience from the Swedish women's lifestyle and health cohort study

Background: The impact of lifestyle changes on cancer risk is yet to be elucidated. We investigated this issue in the Swedish Women's Lifestyle and Health Cohort Study. Material and methods: We measured changes by comparing two questionnaires, filled in 1991/92 and 2003. We followed women for cancer from 2003 until 2012. We used Cox regression models to assess the effect of changes in smoking, alcohol consumption, body mass index (BMI), physical activity and a lifestyle score on the risk of lifestyle-related cancer. One point was added to the lifestyle score for each of these: non-smoking, alcohol consumption ≤12 grams/day, BMI <25 kg/m² and high level of physical activity. Results: We included 29,930 women. From 1991/92 to 2003, median age changed from 40.0 to 51.7 years, alcohol consumption from 2.5 to 4.7 grams/day, BMI from 22.7 to 24.5 kg/m², proportion of current smokers from 31.0 to 20.6% and women reporting high physical activity from 27.2 to 37.0%. Women who quit smoking had lower risk of smoking-related cancers compared to women who continued (hazard ratio (HR) 0.74, 95% confidence interval (CI) 0.55–1.00). Women who reduced their weight by more than 5%, compared to women with stable weight, had lower risk of breast cancer (HR 0.49, 95% CI 0.31–0.78). Among women with score of 0–2 in 1992/93, those who improved to 3-4 had lower risk of lifestyle-related cancers compared to women who did not (HR 0.81, 95% CI 0.66–0.99). Conclusions: Healthy lifestyle changes, particularly smoking cessation and weight reduction, were associated with a decreased risk of cancer.