A study led by the University of Granada has found that men with prostate cancer have lower levels of melatonin compared to those without this illness, regardless of their urinary symptoms and the extent and aggressiveness of the tumor.

This hormone regulates circadian cycles, is produced in the absence of light, and is linked to the light–dark cycle.

A study led by researchers from the Biohealth Research Institute in Granada (ibs.GRANADA) of the University of Granada (UGR) has revealed that men with prostate cancer have lower levels of melatonin, the sleep-inducing hormone, than men who are not suffering this illness, regardless of their urinary symptoms and the extent and aggressiveness of the tumor in question.

This work is part of the CAPLIFE (prostate cancer and lifestyles) Study (principal investigator: Rocío Olmedo Requena of the UGR’s Department of Preventive Medicine and Public Health) and has been published in the Journal of Urology. The work forms part of the results of the doctoral thesis conducted by Macarena Lozano Lorca and supervised by José Juan Jiménez Moleón and Rocío Olmedo Requena.

As Olmedo explains, “circadian cycles regulate many of our bodily functions; they last approximately 24 hours and are regulated by melatonin levels. This hormone is produced in the absence of light and is linked to the light–dark cycle”.

The level of melatonin in the body reaches its peak at night, although its production is affected by age (dropping as we get older) and can be influenced by the seasons (lower during the months of spring–summer). Light pollution can also affect melatonin levels, for example from using electronic devices at night. The International Agency for Research on Cancer classifies night-work as a probable carcinogen, and melatonin may be one of the factors that underlie this link.

Despite the fact that we spend a third of our lives sleeping, to date, little attention has been paid to this important habit and its relationship to health. Sleep studies can be carried out from multiple approaches (sleep duration and quality; shift-work, including night shifts or rotating shifts; level of light pollution, etc.), although the most objective measurement is through analysis of the circadian rhythm based on melatonin levels at different times of day.

To undertake the first-ever analysis of the link between melatonin levels and prostate cancer, in this study, six saliva samples per participant were collected over a 24-hour period, among 40 male subjects recently diagnosed with prostate cancer and 41 men without this pathology. This enabled the researchers to measure the variations in the level of this hormone over the course of the 24 hours, its amplitude (defined by the maximum peak of melatonin production), and the acrophase (time of maximum melatonin peak).

A lower melatonin spike

The scientists observed that, in those subjects with prostate cancer, melatonin levels were systematically lower than in those without this pathology, regardless of age, season of the year, symptoms associated with prostate cancer, and the degree of progression of the disease. In addition, the time of day at which it was produced was later. They concluded that, in the sample under study, melatonin levels in men with prostate cancer—regardless of urinary symptoms, tumor extension, and tumor aggressiveness—were always lower than those of men without this pathology.

This study was carried out at the ibs.GRANADA Institute thanks to collaboration between researchers from the UGR, the International Institute of Melatonin, the Urology Services of the ‘Virgen de las Nieves’ and the ‘Clínico San Cecilio’ Teaching Hospitals, the Andalusian School of Public Health, and the Granada-Metropolitan Health District. In addition, some of the authors of this article are members of CIBERFES and CIBERESP (the Biomedical Research Networking Centers for Fragility and Healthy Aging, and Epidemiology and Public Health, respectively).