发现运动对心理困扰的保护作用随年龄增长而增强，年轻人效果正在减弱。
Age-Dependent Heterogeneity in the Association Between Physical Activity and Mental Distress: A Causal Machine Learning Analysis of 3.2 Million U.S. Adults
- 用因果机器学习分析320万美国成年人数据，发现运动减压效果随年龄上升
- 18-24岁人群运动与心理困扰关联已趋无效（OR=1.01），55-64岁群体保护效应最强（OR=0.50）
- 年轻群体心理危机或非运动可解，适合关注公共健康政策与青年心理健康研究者
体力活动（PA）被广泛认为可缓解心理困扰，但其在不同人群中的保护效果是否系统性差异仍不明确。基于2015-2024年十年美国行为风险因素监测系统（BRFSS）连续十波调查数据（n = 3,242,218），我们研究了休闲时间体力活动与频繁心理困扰（FMD，每月≥14天）在不同年龄组间的异质性关联。加权逻辑回归显示显著年龄梯度：年轻成人（18-24岁）调整后相对危险度（OR）为0.89，55-64岁人群降至0.50，保护效应随年龄单调增强。十年趋势分析表明，年轻人中运动的保护作用持续弱化，2018年与2024年该年龄段的OR均达1.01（无效应）。因果森林通过双重机器学习识别出年龄是治疗效应异质性的主导因素（特征重要性=0.39，为次优预测因子的2.5倍）。经E值敏感性分析、倾向得分重叠检验、安慰剂测试与插补对比验证，结果稳健。研究提示，广为人知的运动—心理健康关联可能无法推广至最年轻成人，其心理困扰或主要由运动难以缓解的压力源驱动。
原文摘要 · Abstract (English)
Physical activity (PA) is widely recognized as protective against mental distress, yet whether this benefit varies systematically across population subgroups remains poorly understood. Using pooled data from ten consecutive annual waves of the U.S. Behavioral Risk Factor Surveillance System (2015-2024; n = 3,242,218), we investigate heterogeneity in the association between leisure-time PA and frequent mental distress (FMD, >=14 days/month) across age groups. Survey-weighted logistic regression reveals a striking age gradient: the adjusted odds ratio for PA ranges from 0.89 among young adults (18-24) to 0.50 among adults aged 55-64, with the protective association strengthening monotonically with age. Temporal analysis across all ten years shows that the young-adult PA effect has been eroding over the past decade, with the 18-24 OR reaching 1.01 (null) in both 2018 and 2024 -- paralleling the deepening youth mental health crisis. Causal Forest via Double Machine Learning independently identifies age as the dominant driver of treatment effect heterogeneity (feature importance = 0.39, 2.5x the next predictor). E-value sensitivity analysis, propensity score overlap checks, placebo tests, and imputation comparisons confirm the robustness of the findings. These results suggest that the well-documented exercise--mental health link may not generalize to the youngest adult population, whose distress appears increasingly driven by stressors that PA alone cannot mitigate.
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