# The Effects of Light Therapy on Cognitive Function and Stress in Women With Breast Cancer Before Systemic Treatment

## TL;DR

This study examined whether light therapy can reduce cognitive issues and stress in women with breast cancer before other treatments, but found limited evidence of its effectiveness.

## Contribution

The study is the first to investigate light therapy's impact on cognitive and stress outcomes in breast cancer patients pre-systemic treatment.

## Key findings

- No significant differences in overall cognitive performance between the blue light and dim light groups.
- The blue light group reported fewer cognitive complaints compared to the dim light group.
- No group differences were observed in biological stress markers like cortisol and α-amylase.

## Abstract

Cancer‐related cognitive impairment (CRCI), for example, impairments in reaction time, processing speed, memory and executive function, may be associated with breast cancer (BC) surgery which can disrupt biological and psychological stress markers. Evidence suggests that light therapy may ameliorate cognitive impairment and stress. In this double‐blind, randomized controlled trial, we investigated the efficacy of light therapy on mitigating the impact of BC surgery on CRCI in a national Icelandic cohort of women with BC.

Participants were randomly allocated to receive circadian‐effective blue light (BL, N = 60) or circadian‐ineffective dim light (DL, N = 57) for 4 weeks after surgery. The primary outcome was overall cognitive performance (assessed via global composite score), and secondary outcomes were specific cognitive domains, cognitive complaints, psychological (depressive symptoms, overall cancer‐related stress and its symptoms: hyperarousal, avoidance, and intrusive thoughts) and biological (cortisol and α‐amylase) stress markers. Linear regression and path analyses within structural equation modeling frameworks were conducted, adjusted for baseline cognitive performance, age, education, subsequent cancer treatment, cancer stage, and treatment credibility.

No group differences were found in overall cognitive performance or in specific cognitive domains, except for a non‐significant trend for faster reaction times in the BL group (p < 0.11). Additionally, the BL group reported significantly fewer cognitive complaints compared with the DL group (p < 0.05), as well as a non‐significant trend for less intrusive thoughts (p < 0.11). No group differences were observed in the biological stress markers.

Overall, these findings suggest that light therapy may help mitigate the adverse effects associated with BC surgery on CRCI and intrusive thoughts, although further research is warranted.

Trial Registration: NCT04418856