Trajectory of physical activity frequency and cancer risk: Findings from a population-based cohort study

BackgroundPhysical 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.MethodsA 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.ResultsFive 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.ConclusionLong-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.