The Impact of Light on the Nighttime Circadian Melatonin Signal and Cancer: The Ugly, The Bad and The Good

David E. Blask PhD MD - Professor of Structural & Cellular Biology - Tulane University School of Medicine: 

The daily (circadian) control of normal rhythms of physiology and metabolism by environmental light is a double-edged sword. Exposure to artificial light at night (LAN), particularly short wavelengths, results in circadian disruption that can be detrimental to our health and wellbeing. Light-mediated circadian disruption, via alterations in the nighttime, circadian anti-cancer melatonin signal from the pineal gland has a significant impact on oncogenesis.

LAN-induced circadian suppression of the melatonin signal in experimental animals results in the dysregulation of melatonin-driven tumor circadian rhythms of metabolism, signaling and cell proliferation leading to increased growth progression and invasion/metastasis of human cancer xenografts and resistance to standard anticancer drug therapies that is prevented by the nocturnal circadian melatonin signal.

Exposure of animals to blue light at daytime, including blue-enriched LED lights, markedly increases the circadian amplitude and duration of the nighttime melatonin signal and markedly slows tumor growth progression and metastasis while increasing tumor sensitivity to cancer therapy. Depending on the time of day or night, exposure to light may have either detrimental or beneficial effects on cancer.