Many systemic functions display circadian rhythms driven by an endogenous mechanism that is regulated by circadian-related genes and these gene expressions control a central clock in the brain and subordinate clocks in peripheral tissues. However, modern life has introduced environmental factors that often interfere with natural circadian rhythms. Importantly, circadian disruption has been identified as an independent risk factor of cancers.

Melatonin is a major circadian rhythm regulator. In cancer patients, the rhythm of melatonin is often disrupted and its level is also reduced.  These changes of melatonin impair its antioxidant and circadian regulatory functions on cells and tissues making them more susceptible to mutations and cancer initiation. In this context, the objectives of this study are to evaluate the sleep quality and blood levels of melatonin in patients with either prostate cancer (PC) or hepatocarcinoma (HCC) with the intent of using its levels as a potential biomarker of the cancers.

The study involved 20 PC and 18 HCC patients, and 26 healthy volunteers. All blood samples were collected in the early morning, at 07:00 hours. Comparative sleep quality between PC, HCC patients and control subjects was acessed with a questionnaire, and melatonin and vitamin D were measured using conventional assays.

The results revealed that patients with the worse sleep quality also had lower values of melatonin and vitamin D compared to control subjects. Notably, expression of melatonin-synthesizing enzymes and specific clock genes (PER, CRY and BMAL1) were significantly reduced and associated with worse prognosis in PC and HCC patients. These findings are consistent with the results of previous studies and suggest that disruption of the circadian rhythms, associated with changes in the light:dark cycle, has consequences for the maintenance of systemic health.

We suggest that supplementation of melatonin and vitamin D may represent the important therapeutic strategies for patients with solid tumors for the purpose of improving their sleep quality and recuperative capacity.