Effect of Constant Illumination and Melatonin Administration on the Lifespan in Rats

The effects of constant illumination, melatonin deficiency, and melatonin administration on the lifespan and oncogenesis in rats were studied in a 55-month experiment. Constant illumination significantly reduced the mean lifespan and maximum age, increased the rate of aging, and increased mortality at the age of 3-12 months. Melatonin administration increased the mean lifespan, maximum age, slowed down aging, and decreased early mortality. Survival analysis (log-rank test, p ⩽ 0.001) and the Cox model confirmed that constant illumination increased the risk of mortality, while melatonin reduced it. Constant illumination was associated with increased incidence of tumor formation, while melatonin reduced the incidence of neoplasms. Tumor-free survival was maximum in the group of animals receiving melatonin and minimum in the group of constant illumination. Thus, constant illumination accelerates aging and increases oncogenic risk, while melatonin has a geroprotective and anti-carcinogenic effects.