Bright light therapy influences glymphatic system function in individuals with subthreshold depression: a randomized clinical tria – Pan Chen, Guanmao Chen, Zixuan Guo, Ruoyi Chen, Xinyue Tang, Zibin Yang, Wenhao Ma, Chao Chen, Shilin Sun, Yuan Zhang, Hui Zhong, Shu Zhang, Zhangzhang Qi, Wenjie Fang, Lijun Jiang, Zhinan Yin, Li Huang, Junxian Ma, Qian Tao, Ying Wang

Objective

Identify the effects of 8 weeks of daily 30-minute morning bright light therapy compared with a placebo inactive light device on glymphatic system function, brain activity, inflammation, and depressive symptoms in individuals with subthreshold depression.

Method

Randomized, double-blind, placebo-controlled trial.

Adults aged 18 to 28 years with subthreshold depression (n = 110).

Participants received either bright light therapy (5000 lx, 30 min/day; n = 57) or placebo inactive light treatment (n = 53) for 8 weeks. Assessments included depressive symptom scales, MRI-based glymphatic markers, resting-state functional MRI, and serum inflammatory cytokines.

Conclusion

Bright light therapy improved depressive symptoms and enhanced glymphatic system function in individuals with subthreshold depression. Improvements in glymphatic function were associated with reduced inflammation, increased prefrontal cortex activity, and alleviation of depressive symptoms, particularly anhedonia. These findings support bright light therapy as a promising nonpharmacological intervention for early depressive symptoms.