Humans evolved to the rhythms of the natural light-dark cycle of day and night. The spread of artificial lighting means most of us no longer experience truly dark nights.
Research suggests that artificial light at night can negatively affect human health, increasing risks for obesity, depression, sleep disorders, diabetes, breast cancer and more.
Like most life on Earth, humans adhere to a circadian rhythm — our biological clock — a sleep-wake pattern governed by the day-night cycle. Artificial light at night can disrupt that cycle.
Our bodies produce the hormone melatonin in response to circadian rhythm. Melatonin helps keep us healthy. It has antioxidant properties, induces sleep, boosts the immune system, lowers cholesterol, and helps the functioning of the thyroid, pancreas, ovaries, testes and adrenal glands. Nighttime exposure to artificial light suppresses melatonin production.
Here are some articles to research that has been done on the effects of lighting on our health:
This 2009 study by Dr. Richard Stevens, of the University of Connecticut, compared cancer rates and the presence of light at night across 164 countries and found that women in industrialized, highly lit countries had a 30 to 50 percent higher risk of breast cancer than those in countries with less light pollution.
This summary from Harvard University states “Study after study has linked working the night shift and exposure to light at night to several types of cancer (breast, prostate), diabetes, heart disease, and obesity. It’s not exactly clear why nighttime light exposure seems to be so bad for us. But we do know that exposure to light suppresses the secretion of melatonin, a hormone that influences circadian rhythms, and there’s some experimental evidence (it’s very preliminary) that lower melatonin levels might explain the association with cancer.”
Light at Night, Shiftwork, and Breast Cancer Risk
J Natl Cancer Inst (2001) 93 (20): 1513-1515.
Night shift work, light at night, and risk of breast cancer.
Davis S, Mirick DK, Stevens RG
Journal of the National Cancer Institute. J Natl Cancer Inst. 2001 Oct 17;93(20):1557-62.
Missing the Dark: Health Effects of Light Pollution
Environmental Health Perspectives
2009 Jan; 117(1): A20–A27.