Evaluating chronotypically tailored light therapy for breast cancer survivors: Preliminary findings on fatigue and disrupted sleep.

More than one-third of cancer survivors experience significant residual symptoms after treatment completion. Fatigue and sleep disruption often co-occur and exacerbate each other. The purpose of this preliminary analysis was to examine the effect of a chronotypically tailored light therapy on fatigue and sleep disruption in female survivors 1-3 years post-completion of chemotherapy and/or radiation for stage I to III breast cancer. The data for this analysis were collected as part of an ongoing two-group randomized controlled trial (NCT03304587). Participants were randomized to receive either bright blue-green light (experimental) or dim red light (control). Light therapy was self-administered using a light visor cap at home. Both groups received 30-min daily light therapy for 14 consecutive days either between 19:00 and 20:00 h (for morning chronotypes) or within 30 min of waking in the morning (for evening chronotypes). Fatigue and sleep quality were self-reported using the Patient-Reported Outcomes Measurement Information System (PROMIS)-Fatigue, PROMIS-Sleep Disturbance, Pittsburgh Sleep Quality Index, and a daily log before (pre-test) and following the light intervention (post-test). Linear mixed model analysis or generalized estimating equations examined group difference overtime adjusting for pre-test scores. No between-group differences were found. However, after adjusting for the baseline fatigue, the experimental group reported significant decreases in fatigue (p < .001) and sleep disturbance (p = .024) overtime. The experimental group also reported significantly better subjective sleep quality after 14 d of light therapy (p = .017). Positive trends in sleep latency, sleep duration, night-time awakenings, and early morning awakenings were also observed. Unexpectedly, sleep disturbance significantly decreased in the control group (p = .030). Those who received dim light control reported significantly shorter sleep latency (p = .002), longer total sleep time (p = .042), and greater habitual sleep efficiency (p = .042). These findings suggest that bright light therapy significantly improved post-treatment fatigue and subjective sleep quality in breast cancer survivors. Although it remains to be confirmed, the findings additionally show unexpected benefits of dim light on sleep. Properly timed light exposure may optimize the therapeutic effect and can be the key for successful light therapy. How the administration timing coupled with wavelengths (short vs. long) and intensity of light affecting fatigue and disrupted sleep requires further investigation.