What pregnant women should do in the hours before bedtime


Pregnant women should dim the lights and turn off screens in the three hours before bedtime to prevent gestational diabetes, scientists have advised.

The warning follows a study of more than 700 pregnant women by Northwestern University, which found that women who developed the condition had greater light exposure in the hours before going to sleep.

Gestational diabetes happens when the body cannot produce enough insulin to control higher levels of blood sugar in pregnancy and can lead to premature and stillbirth, pre-eclampsia or the need for a caesarean section.

Growing evidence suggests exposure to light at night before bedtime may be linked to impaired blood sugar regulation in non-pregnant adults.

However, little was known about the effect of evening light exposure during pregnancy on the risk of developing 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.

“It’s alarming. 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.”

‘Keep screens as dim as possible’

In Britain, gestational diabetes affects four to five in 100 women, and if a woman has it in her first pregnancy she is more likely to also have it in subsequent pregnancies.

Previously studies have shown that obesity is a major risk factor, but researchers now think that bright light exposure from devices like TVs, computers and smartphones before sleep may also be having a major impact.

Experts believe that too much light before bedtime may affect glucose metabolism by activating a ‘fight or flight’ response, causing the heart rate to rise at a time when the body should be winding down - a state known as sympathetic overactivity.

Research shows that 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.

“We don’t think about the potential harm of keeping the environment bright from the moment we wake up until we go to bed,” added Dr Kim.

“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.

“Try to reduce whatever light is in your environment in those three hours before you go to bed. 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.”

‘Importance of reducing light exposure’

Dr Kim said the findings had led to her changing her own behaviour.

“Now I’m the light police at home,” she said “I see all this light I never thought about before. I try to dim the light as much as possible.”

For the new study, 741 women in their second trimester were asked to wear an actigraph on their wrists to measure their light exposure, and also received 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.

Women with the highest levels of bright light in the three hours before bed were five times more likely to develop gestational diabetes than those who dimmed their lighting at night time.

“This study highlights the importance of reducing light exposure in the hours before bedtime” added senior author Kathryn Reid, research professor of neurology at Feinberg at Northwestern.

The study was published in the American Journal of Obstetrics and Gynecology Maternal Fetal Medicine.