Melatonin secretion following brain midline irradiation is diminished, but not correlated with subjective sleep disturbances.

Objective: Cranial irradiation for brain tumours or leukaemias has been related to cognitive, endocrine and psychosocial late effects as well as sleep disturbances and increased daytime sleepiness. Studies suggest that cranial irradiation might impact on pineal melatonin secretion. Melatonin is an important regulator in human circadian rhythms and the sleep-wake cycle. The objective of this study was to investigate melatonin secretion, subjective sleep parameters and their interplay in a cohort of cranially irradiated head and brain tumour and leukaemia survivors at least 3 years after radiotherapy.
Design: Cross-sectional study.
Patients: Thirty-eight adults.
Measurements: Melatonin secretion was evaluated by measuring its metabolite 6-sulphatoxymelatonin in collected overnight urine. Subjective sleep quality and daytime sleepiness were assessed using the Pittsburgh Sleep Quality Index and the Epworth Sleepiness Scale. The Beck Depression Inventory II was used to screen for depressive symptoms because of their impact on sleep.
Results: Patients irradiated in the brain midline had significantly lower melatonin secretion (P = 0.008). Subjects exhibited a high prevalence of sleeping difficulties, daytime sleepiness and depression, with females and overweight subjects particularly affected. Melatonin values and subjective sleep parameters did not correlate with each other or with treatment and most patient variables.
Conclusions: Our data suggest that radiation exposure to the pineal gland negatively affects melatonin secretion. This lack of pineal melatonin does not influence subjective sleep quality. As melatonin has important antioxidant and cancer-protective effects, further research is necessary to elucidate whether these patients have an increased risk of developing secondary neoplasms and other radiation late effects.
(© 2018 John Wiley & Sons Ltd.)