New research has found that the amount of daylight a woman is exposed to during late pregnancy could influence her risk of developing postnatal depression.
Carried out by researchers at San José State University and the University of California San Francisco, and published in the Journal of Behavioral Medicine, the new study looked at 293 women who were all first-time mothers.
The researchers gathered data on the amount of daylight the women were exposed to during the final trimester of their pregnancy, along with information about known risk factors for postpartum depression, including a history of depression, age, socioeconomic status and how much she slept.
The findings suggested that the number of daylight hours a woman was exposed to during her final month of pregnancy, as well as just after birth, influenced her risk of developing depressive symptoms.
Among women whose final trimester coincided with late summer to autumn, when days were shortening, the risk of depressive symptoms was highest (35 per cent), with these symptoms also continuing to be more severe following the birth of their babies.
Women whose final trimester coincided with seasons with longer daylight hours had the lowest risk of depression, which was 26 per cent.
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The findings are also in line with what is already known about the relationship between reduced exposure to natural light and the risk of depression in the general population.
Lead author Deepika Goyal commented that the results suggest that if the late third trimester and birth occur when the days are shorter, using light therapy may help to reduce postpartum depressive symptoms. In addition, health experts should be encouraging women to spend more time outdoors to help increase light exposure.
"Women should be encouraged to get frequent exposure to daylight throughout their pregnancies to enhance their vitamin D levels and to suppress the hormone melatonin," explains Goyal. "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. Likewise, early morning or late evening walks may be relaxing but would be less effective in increasing vitamin D exposure or suppressing melatonin."
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