Pregnant women should dim lights before bed to cut gestational diabetes risk, says study

Expecting mothers should dim the lights and turn off, or at least turndown, their screens a few hours before bed to reduce the risk of gestational diabetes mellitus, according to researchers at Northwestern University.

The study, published on Friday in the American Journal of Obstetrics and Gynecology Maternal Fetal Medicine, found that women who developed the condition had greater light exposure in the three hours before sleep.

“It seems there is inappropriate activation of the fight or flight response when it is time to rest,” Dr Minjee Kim, who lead the study, said.

The study did not identify what percentage increase is associated with the risk, with Dr Kim saying "we have more to prove", but said light exposure "remained significantly associated with gestational diabetes".

Gestational diabetes mellitus is a common pregnancy complication with significant health risks for both mother and unborn child.

In 2020, the rate of gestational diabetes was 7.8 per cent of all births in the US. It is known to increase obstetric complications, the mother's risk of diabetes, heart disease and dementia, as well as the child's risk of obesity and hypertension as they grow up. Data shows 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.

The study of 741 women in their second trimester was conducted at eight clinical US sites. 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 for factors including age, BMI, race/ethnicity, season, sleep duration, sleep regularity index and daytime light exposure, pre-sleep light exposure remained significantly associated with gestational diabetes.

Scientists do not know what source of bright light causes the problem, but it might all add up, according to Dr Kim, who is an assistant professor of neurology at Northwestern University Feinberg School of Medicine, Chicago, and a Northwestern Medicine neurologist.

She 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.”

In addition to dimming the lights, losing weight and exercising also reduce the risk of developing gestational diabetes.

Dr Kim said: “Turning down the lights is an easy modification you can make.”

The study suggests that light exposure before bedtime may be an under-recognised yet easily modifiable risk factor of gestational diabetes.