Nighttime light exposure suppresses the hormone melatonin, which plays an important role in regulating sleep and circadian rhythms. Light exposure during nighttime hours causes shifts to the timing of circadian rhythms, initiating a reset of the body’s biological clock that can contribute to a wide range of health problems.
Let’s take a look at what we know about five common health conditions that science has linked to nighttime light exposure.
Nighttime exposure to artificial light has been linked to increased incidence of obesity. A 2012 study of older adults in Japan found a significant association between higher body weight and the intensity of exposure to artificial light at night. Significantly, this association existed independent of melatonin levels, indicating that there may another mechanism by which light contributes to increased body weight. Higher levels of nighttime light exposure were also linked to larger waist circumference and a greater likelihood of obesity.
Diabetes is a metabolic disorder that affects more than 29 million Americans. A compelling body of scientific research indicates that nighttime light exposure disrupts metabolic function, at least in part as a result of disruption to circadian rhythms. Research shows connections between diabetes and circadian rhythm disruption, as well as between diabetes and nighttime light exposure.
High blood pressure
More than 70 million American adults—roughly 29 percent of the population—suffer from high blood pressure. Treatment rates have climbed, but millions of Americans still aren’t receiving treatment for their high blood pressure. Recent research links nighttime light exposure to high blood pressure, likely through light’s suppressive effects on melatonin.
Blood pressure fluctuates over the course of a 24-hour day and night, and like so many other of the body’s processes, is regulated by circadian rhythms. Blood pressure is typically higher in the daytime and lower throughout the night. Melatonin, released by the body during evening hours, has a lowering effect on blood pressure.
A growing body of research indicates that nighttime light exposure may be linked to several forms of cancer, including breast cancer. An international study that included 164 countries found that breast cancer risk was elevated by 30-50 percent in nations with the highest levels of nighttime light exposure, compared to nations with the lowest.
Research also indicates that nighttime exposure to bright light may accelerate breast cancer tumor growth, and that even dim light exposure at night may lead some types of breast cancer tumors to become resistant to some forms of treatment.
Light exposure at night is linked to several conditions that in turn contribute to cardiovascular problems. Evening light exposure disrupts and minimizes sleep. Both insufficient sleep and poor quality sleep are linked to increased risks for cardiovascular disease. Changes to melatonin levels—which occur as a result of nighttime light exposure—may contribute to heart disease, as well as to higher cholesterol levels and high blood pressure. Obesity, which is linked to evening light exposure and to circadian rhythm disruption, is a significant risk factor for heart disease. Evening light exposure also is linked to metabolic dysfunction. Metabolic disorders such as metabolic syndrome increase risks for cardiovascular disease.
What are the Risks? The 5 Health Dangers of Nighttime Light Exposure