October 08, 2018
2 min read

Fewer daylight hours in late pregnancy linked to depression

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Image of Deepika Goyal
Deepika Goyal

First-time mothers in their third trimester of pregnancy during the seasons with shorter daylight hours were at greater risk for postpartum depression, according to findings published in Journal of Behavioral Medicine.

Less daylight during months with short day lengths may influence levels of vitamin D and melatonin, which may put pregnant women at further risk for depression, Deepika Goyal, PhD, MSN, professor of nursing at San Jose State University Valley Foundation School of Nursing, and colleagues explained.

“Although reduced exposure to natural light has been associated with depression among adults in the general population, conflicting research exists regarding the effect of light exposure or seasonality on depressive symptoms during pregnancy and postpartum,” they wrote.

In this secondary analysis, researchers examined whether seasonal light exposure impacted depressive symptoms in late pregnancy and the first 3 months postpartum after controlling for known risk factors such as depression history, age and low socioeconomic status using linear mixed models and multiple linear regression.

“It is important to examine non-pharmacological methods to prevent/reduce risk of developing depression,” Goyal told Healio Psychiatry. “Often women are reluctant to take medication that can potentially harm the fetus.”

They assessed depressive symptoms in 279 women expecting their first child using the Center for Epidemiologic Studies Depression Scale as well as their stress levels using the Perceived Stress Scale and sleep duration using a wrist activity tracker. Day lengths were categorized into short (Nov. 5 to Feb. 4), lengthening, (Feb. 5 to May 4) long (May 6 to Aug.4) and shortening (Aug. 5 to Nov. 4).

Overall, 273 participants had data for all four time points. Analysis revealed that day length at the late third trimester had an effect on the trajectory of depressive symptom scores over time (P = .024). Post hoc analysis indicated that during the third trimester, depressive symptom scores during the shortening day length were higher over time (P = .005) than the other three types of day lengths. The overall rate for risk of depression was 30% in the third trimester and 22% at 3 months postpartum, according to the results.

The investigators found that the lowest risk for depression (26%) occurred during the short length period and was highest (35%) during the shortening day length period. Women who gave birth during the shortening day length time frame experienced higher depressive symptom scores over time (95% CI, 11.8-14.1) compared with those who gave birth during the other three types of day length (95% CI, 10.8-11.9). Women who gave birth during the shortening day length time frame were also at greater risk for depression.

“Women giving birth or who are in the postpartum period during months with shortening days may be at risk of developing depressive symptoms depending on where they live and how much outdoor light exposure they get,” Goyal told Healio Psychiatry. “Clinicians should be more vigilant with these women, particularly if there are other risk factors present during the third trimester.”

Furthermore, Goyal and colleagues found that the type of day length during the late third trimester predicted postpartum depressive symptoms at 3 months, even after controlling for mental health history and third trimester depressive symptom scores.

“Our study findings have several implications for clinical practice, including encouraging frequent exposure to daylight throughout the pregnancy to enhance vitamin D levels and suppress melatonin,” the researchers wrote.

“Ensuring daylight exposure is particularly important for women living in higher latitudes where day light exposure is even shorter than in northern California,” they continued. “Clinicians should encourage women to get more exercise outdoors when weather and safety permit. Daily walks during daylight hours may be more effective in improving mood than walking inside a shopping mall or using a treadmill in a gym.”

Disclosure: The authors report no relevant financial disclosures.