For pregnant women or those planning a pregnancy, it may be best to keep late-night light exposure to a minimum. According to a recent study, exposure to artificial light during the evening hours can seriously affect a woman's reproductive health and even mess with the health of her unborn child.

Darkness Starts An Important Chemical Process

Researchers from the University of Texas Health Science Center in San Antonio explored the importance of darkness for a woman’s reproductive health and the health of her unborn child, and came up with some pretty astonishing findings, Live Science reported. According to their research darkness plays a big role in ensuring fertility and protecting the developing fetus. It’s not exactly the artificial light that interferes with a woman’s body, but the internal chemical reaction that prolonged exposure to light stunts.

Melatonin, The Sleepy Chemical

Melatonin is a hormone secreted by our pineal glands. Exposure to darkness stimulates its release and the presence of melatonin in our systems helps to induce drowsiness, thus aiding in the sleep process. “Every time you turn on the light at night, this turns down the production of melatonin,” Russell Reiter, a researcher involved with the study, told Live Science. In women who are trying to conceive, melatonin helps to protect eggs from damage, especially during ovulation. Reiter advises women who are hoping to conceive to “maintain at least eight hours of a dark period at night." Doing this should be a consistent thing, because otherwise a woman's biological clock can become confused.

In women who are already pregnant, interference with melatonin levels can also mess with the unborn child. If the fetus does not get the proper amount of melatonin from their mother, their biological clock can also become confused. This has been linked to behavioral problems such as attention deficit hyperactivity disorder (ADHD) or autism in young children.

Your Biological Clock

Light pollution is defined as excessive, misdirected, or obstructive artificial light. Other than being an annoyance for stargazers, the overabundance of artificial light during the evening can be a health issue because it messes with our circadian rhythm, also known as the body clock. "We have evolved for four million years with a regular light-dark cycle that regulates circadian rhythms," Reiter said. "We have corrupted this with the development of artificial light, which disrupts the biological clock at night and suppresses levels of melatonin."

It’s not just women who are pregnant or looking to conceive that need to be careful about overexposure to artificial light. The International  Agency for Cancer Research classified night work as a probable human carcinogen due to the undeniable link between night workers and the increased risk of developing breast cancer.

How To Avoid Prolonged Exposure To Light

The study clearly noted that it's darkness, not sleep, that causes these issues with female fertility. Although sleep is equally important, it’s the darkness that is needed for the production of melatonin.

Women can take steps to ensure nighttime darkness by efficiently sealing windows and doors, turning off televisions and other electronic glares. If a night light is truly needed, Reiter suggests that one with a red or yellow glow, as opposed to a white or blue light, would do minimal damage to one’s circadian rhythm. 

On a global level many cities have taken measures to cut down on the amount of artificial lights that are kept on during late and early hours. Even Paris, the city of lights, has passed laws prohibiting storefronts and office buildings from having lights on between the hours of 1 a.m. and 7 a.m., The Sci Show reported.

Source: Reiter RJ, Tamura H, Tan DX, Xu XY. Melatonin and the circadian system: contribution to successful female reproduction. Fertility and Sterility. 2014