Synergistic Effects of Body Mass Index in Early Adulthood and Recent Weight Gain in Reducing Mortality Risk Among Cancer Survivors

Cancer survivors face an elevated risk of mortality, and changes in body mass index (BMI) may play a critical prognostic role. This study examined BMI variations during early adulthood and recent years in relation to cancer-specific mortality and all-cause mortality. Data were drawn from the National Health and Nutrition Examination Survey. Statistical models were applied to evaluate associations, dose-response relationships, and threshold effects. Among 2,024 cancer survivors, recent BMI increases were significantly associated with reduced cancer and all-cause mortality, whereas earlier BMI changes showed weaker associations. Compared with those in the lowest tertile, those with greater recent BMI increases had a 24%-44% lower risk of cancer mortality (P for trend = 0.016) and a 34%-45% lower risk of all-cause mortality (P for trend < 0.001). A non-linear association was identified, with a 5% BMI increase as the threshold; each 1% gain below this threshold was linked to a 4% mortality risk reduction (p < 0.001). Joint analysis revealed that a high early BMI combined with a ≥ 5% recent BMI increase significantly reduced mortality risk. Moderate recent weight gain may improve survival among cancer survivors, underscoring the importance of individualized weight management strategies.