Light at night linked to high blood pressure, diabetes

Yet another study finds adverse effects of light at night, this time showing that the profound suppression of melatonin could lead to higher blood pressure, diabetes, and poor sleep.

Elizabeth Armstrong Moore
Elizabeth Armstrong Moore is based in Portland, Oregon, and has written for Wired, The Christian Science Monitor, and public radio. Her semi-obscure hobbies include climbing, billiards, board games that take up a lot of space, and piano.
Elizabeth Armstrong Moore
2 min read


I don't know a single person who, from dusk to dozing off, isn't exposed to some kind of electrical lighting, especially in these darkest of winter days. Unfortunately, study after study is coming out linking this nighttime lighting to various ailments, almost always due to the effect light has on melatonin suppression.

The latest findings, via a study just accepted for publication in The Journal of Clinical Endocrinology & Metabolism, finds that exposure to electrical light between dusk and bedtime "strongly suppresses melatonin levels and may impact physiological processes regulated by melatonin signaling, such as sleepiness, thermoregulation, blood pressure, and glucose homeostasis."

So not only have researchers recently found links between light at night and cancer and depression, there is now reason to further investigate its effect on blood pressure and diabetes.

"On a daily basis, millions of people choose to keep the lights on prior to bedtime and during the usual hours of sleep," says lead author Joshua Gooley of Brigham and Women's Hospital and Harvard Medical School in Boston in a news release. "Given that chronic light suppression of melatonin has been hypothesized to increase relative risk for some types of cancer and that melatonin receptor genes have been linked to type 2 diabetes, our findings could have important health implications for shift workers who are exposed to indoor light at night over the course of many years."

The hormone melatonin is produced (at night, or now it seems, in darkness) by the pineal gland in the brain. It plays a role regulating the sleep-wake cycle and also in lowering blood pressure and body temperature.

For this study, researchers inserted an intravenous catheter into the arms of 116 healthy volunteers ages 18 to 30--who were exposed to dim or room light in the eight hours preceding bedtime for five consecutive days--to measure melatonin every 30 to 60 minutes.

Those exposed to room light produced melatonin about 90 minutes less each night than those exposed to dim light. Moreover, exposure to room light during sleep hours suppressed melatonin production by more than 50 percent.

The researchers say more work needs to be done to substantiate melatonin suppression as a significant risk factor for cancer, as well as to study the mechanisms by which melatonin regulates glucose metabolism, but at this point, light at night is looking increasingly pernicious.