# Light pollution / circadian disruption

Artificial light at night (ALAN), from streetlights, screens, and indoor bulbs, throws off your body clock. It works through special cells in your retina (ipRGCs, which carry a pigment called melanopsin) that are most sensitive to short-wavelength blue light around 480 nm. When that light hits them at night, it suppresses melatonin and shifts your master clock, which sits in a brain region called the suprachiasmatic nucleus. Chronically knocking your clock out of alignment is linked to weaker immunity, metabolic problems, heart risk, and faster epigenetic aging. Work by Erren and colleagues, plus several big cohort studies, has tied nighttime light exposure to higher rates of breast and prostate cancer, possibly through melatonin's effect on cell growth. And since cities keep getting brighter, the health effects of our light environment, indoors and out, are only becoming more relevant.

## Sources

- Blask DE, Brainard GC, Dauchy RT, Hanifin JP, Davidson LK, Krause JA, Sauer LA, Rivera-Bermudez MA, Dubocovich ML, Jasser SA, Lynch DT, Rollag MD, Zalatan F. (2005). Melatonin-depleted blood from premenopausal women exposed to light at night stimulates growth of human breast cancer xenografts in nude rats. Cancer Research. https://doi.org/10.1158/0008-5472.CAN-05-1945

---

_Canonical: https://longevity-switzerland.com/en/glossary/light-pollution-circadian · Part of Longevity Cities · Updated 2026-06-22_