ObjectiveThis study examined relationships between weight‐change trajectories and all cancers and obesity‐related cancer risks.MethodsA total of 1,882,304 men and 899,912 women from the 2002 to 2017 National Health Insurance Service cohort were included. Weight‐change trajectories in 2002 to 2009, according to BMI, were determined using group‐based trajectory modeling. Cox proportional hazards regression assessed associations between trajectories and cancer incidence.ResultsOverall, >50% of individuals maintained stable weight, as did two‐thirds of those in the overweight and obesity groups. A total of 64,725 men and 37,608 women developed incident cancer. Weight stability in overweight or obesity groups was associated with greater cancer risk. In both sexes, higher weight across BMI groups increased risks of all cancers, obesity‐related cancers and thyroid, colorectal, stomach, liver, prostate, and postmenopausal breast cancer. Stratified by BMI, weight gain increased risks of all cancers and obesity‐related cancers in men with obesity class I and women with overweight. Weight loss decreased risks of obesity‐related cancers, thyroid cancer, and kidney cancer among men with overweight, premenopausal breast, endometrial, and ovarian cancer in women with overweight, and obesity‐related cancers and thyroid cancer in women with class I obesity.ConclusionsMaintaining weight and avoiding weight gain are crucial for reducing cancer risk, but achieving a stable, normal BMI optimizes cancer prevention.
Background Physical activity (PA) changes throughout an individual’s life, but the association between such changes and cancer risk seems to be overlooked in the literature. Thus, this study aimed to examine the association between the trajectories of PA frequency and cancer incidence among middle-aged Korean adults. Methods A total of 1,476,335 eligible participants (992,151 men and 484,184 women) aged ≥40 years from the National Health Insurance Service cohort (2002–2018) were included. Assessment of PA frequency was a self-reported measure, based on the question: “How many times per week do you perform exercise that makes you sweat?”. PA frequency trajectories (i.e., trajectory classes of change in PA frequency) from 2002 to 2008 were identified using group-based trajectory modeling. Cox proportional hazards regression was used to assess the associations between the PA trajectories and cancer incidence. Results Five PA frequency trajectories over 7 years were identified: persistently low (men:73.5%; women:74.7%), persistently moderate (men:16.2%; women:14.6%), high-to-low (men:3.9%; women:3.7%), low-to-high (men:3.5%; women:3.8%), and persistently high (men:2.9%; women:3.3%). Compared with persistently low frequency, maintaining a high PA frequency was associated with a lower risk of all cancers (Hazard ratio (HR) = 0.92, 95%CI = 0.87–0.98) and breast cancer (HR = 0.82, 95%CI = 0.70–0.96) among women. There was a lower risk for thyroid cancer among men in the high-to-low (HR = 0.83, 95%CI = 0.71–0.98), low-to-high (HR = 0.80, 95%CI = 0.67–0.96), and high PA trajectories (HR = 0.82, 95%CI = 0.68–0.99). There was a significant association between moderate trajectory and lung cancer in men (HR = 0.88, 95%CI = 0.80–0.95), in both smoking and non-smoking men. Conclusion Long-term persistent high frequency of PA as part of the daily routine should be widely promoted and encouraged to reduce the risk for all cancer development in women.
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