Canadian Environmental Health Atlas

Understanding Our Environment is Key to Promoting Health and Preventing Disease

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The Light-at-Night Theory

The Light-at-Night Theory

The Light-at-Night Theory
The light-at-night (LAN) theory, which is based primarily on animal and experimental studies, proposes that exposure to light affects many biological processes by lowering the production of the hormone melatonin.1 Over a 24-hour period of light and dark, we experience circadian rhythms—changes in body temperature, heart rate, insulin production, and other processes—that are regulated in part by melatonin. Melatonin affects our sleeping and feeding patterns.

Melatonin is normally produced at night by the pineal gland. When we are exposed to light, production slows in a dose-response manner: the brighter the light, the less melatonin we produce. Exposure to light at even a moderate level suppresses melatonin production, with brighter lights and longer exposure resulting in more suppression. With less melatonin to regulate biological processes and sleep-wake cycles, our health may be affected in a number of ways. Awareness of the relationship between melatonin production and our health has led some researchers to consider the possible effect of prolonged exposure to light on shift workers.

 

  • 1. Stevens RG. Electric power use and breast cancer: a hypothesis. Am J Epidemiol. 1987;125(4):556-561.