Exposure to light for a longer duration just before bedtime increases the likelihood of developing gestational diabetes in pregnant women.
According to a new study from Northwestern Medicine, to decrease the chance of developing gestational diabetes mellitus, pregnant individuals should lower the brightness of lights in their home and turn off or dim their screens, such as computer monitors and smartphones, several hours before bedtime.
In the multi-site study, women who were diagnosed with gestational diabetes mellitus had higher light exposure in the three hours leading up to sleep. However, their exposure to light during daytime or sleep, as well as their activity levels, did not differ from those who did not develop gestational diabetes.
“Our study suggests that light exposure before bedtime may be an under-recognized yet easily modifiable risk factor of gestational diabetes,” said lead study author Dr. Minjee Kim, assistant professor of neurology at Northwestern University Feinberg School of Medicine and a Northwestern Medicine neurologist.
Growing evidence suggests exposure to light at night before bedtime may be linked to impaired glucose regulation in non-pregnant adults. However, little is known about the effect of evening light exposure during pregnancy on the risk of developing gestational diabetes, a common pregnancy complication with significant health implications for both mother and offspring.
This is believed to be one of the first multi-site studies to examine light exposure before sleep on the risk of developing gestational diabetes.
The study was recently published in the American Journal of Obstetrics and Gynecology Maternal Fetal Medicine.
Gestational diabetes rise is ‘alarming’
Gestational diabetes is on the rise in the U.S. and globally. About 4.5% of first-time pregnant women with a baby born between 2011 and 2013 developed gestational diabetes, which has been increasing on average by 3.4% per three-year period until 2019. In 2020, the rate of gestational diabetes was 7.8% of all births in the U.S.
“It’s alarming,” Kim said. “Gestational diabetes is known to increase obstetric complications, and the mother’s risk of diabetes, heart disease, and dementia. The offspring also are more likely to have obesity and hypertension as they grow up.”
Data show that women who have gestational diabetes are nearly 10 times more likely to develop type 2 diabetes mellitus compared to those who do not have glucose issues during pregnancy, Kim said.
Bright light exposure prior to sleep can come from bright lights in your home and from devices like TVs, computers, and smartphones.
“We don’t think about the potential harm of keeping the environment bright from the moment we wake up until we go to bed,” Kim said. “But it should be pretty dim for several hours before we go to bed. We probably don’t need that much light for whatever we do routinely in the evening.”
Scientists don’t know which source of bright light causes the problem, but it might all add up, Kim said.
“Try to reduce whatever light is in your environment in those three hours before you go to bed,” Kim said. “It’s best not to use your computer or phone during this period. But if you have to use them, keep the screens as dim as possible,” Kim said, suggesting people use the night light option and turn off the blue light.
If pregnant persons develop gestational diabetes with the first pregnancy, they are more likely to have it with the next pregnancy.
Pre-sleep light exposure increases heart rate and may lead to abdominal obesity, insulin resistance, increased blood pressure
Pre-sleep light exposure may affect glucose metabolism through sympathetic overactivity, meaning the heart rate goes up before bed when it should go down. “It seems there is inappropriate activation of the fight or flight response when it is time to rest,” Kim said.
Data shows the sympathetic overactivity may lead to cardiometabolic disease, which is a cluster of conditions including abdominal obesity, insulin resistance, increased blood pressure and an imbalance of lipids, all leading to cardiovascular disease.
The study of 741 women in their second trimester was conducted at eight clinical U.S. sites between 2011 and 2013. The participants’ light exposure was measured by an actigraph worn on their wrists. The women were measured during the second trimester of pregnancy, the time when they receive routine screening for gestational diabetes.
After adjusting separately for age, BMI, race/ethnicity, education, commercial insurance, employment schedule, season, sleep duration, sleep midpoint, sleep regularity index, and daytime light exposure, pre-sleep light exposure remained significantly associated with gestational diabetes.
The growing rate of gestational diabetes has been partially attributed to increasing body mass index and the older age of pregnant persons.
“But even after adjusting for BMI and age, gestational diabetes is still rising,” Kim said. “We have a lot to prove, but my personal worry is that light may be silently contributing to this problem without most people realizing the potential harm.”
Losing body weight and exercising also reduce the risk of developing gestational diabetes, which are important but take some effort.
Turning down lights is an easy modification
“Turning down the lights is an easy modification you can make,” Kim said.
“Now I’m the light police at home,” Kim said. “I see all this light I never thought about before. I try to dim the light as much as possible. Just for evening activities such as dinner and bathing the kids, you don’t need bright light.”
“This study highlights the importance of reducing light exposure in the hours before bedtime,” said senior author Kathryn Reid, research professor of neurology at Feinberg.
Reference: “The association between light exposure before bedtime in pregnancy and the risk of developing gestational diabetes mellitus” by Minjee Kim, Francesca L. Facco, Rosemary I. Braun, Michael S. Wolf, Blas Garcia-Canga, William A. Grobman, Phyllis C. Zee and Kathryn J. Reid, 10 March 2023, American Journal of Obstetrics & Gynecology MFM.
The study was funded by the National Heart, Lung, and Blood Institute of the National Institutes of Health.
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