Women who give birth in winter are more at risk of postnatal depression, a study has found.
Those who enter their final trimester during ‘shortening’ daylight hours are 29 per cent more likely to suffer from the mental-health condition.
In the northern hemisphere, this runs from August 5 to November 4 when there is 12 hours of daylight, according to the researchers. The third trimester begins at 28 weeks.
Sunlight is thought to trigger the production of the hormone serotonin, which boosts a person’s mood and helps them feel calm.
The switch from the long days of summer to short winter days is thought to trigger depression in expectant mothers.
Women who conceive early in the year are more at risk of postnatal depression (stock)
The researchers at San José State University analysed two studies with a total of 293 women.
These trials investigated the amount of daylight the women were exposed to during the last trimester of their pregnancies.
All of the participants were first-time mothers from California.
They also completed a questionnaire that assessed how often they experienced depression symptoms within the first three months of parenthood.
These symptoms included insomnia, a loss of appetite and feeling lonely.
Results, published in the Journal of Behavioral Medicine, suggest pregnant women have a 30 per cent risk of developing postnatal depression overall.
This risk falls to just 26 per cent among those who are in their third trimesters during ‘long’ daylight hours – which the researchers defined as being from May 6 to August 4.
Women who are in their final stage of pregnancy between August and early November – ‘short’ days – are the most at risk, with a 35 percent chance of suffering from postnatal depression.
These women’s symptoms are also more severe if the condition does develop.
‘Among first-time mothers, the length of day in the third trimester, specifically day lengths that are shortening compared to day lengths that are short, long or lengthening, were associated with concurrent depressive symptom severity,’ lead author Dr Deepika Goyal said.
The researchers recommend women with a history of depression who are in the final stage of their pregnancies during the short daylight months use light boxes.
This involves sitting in front of a light-emitting box for around half-an-hour at the start of each day.
Although evidence of their effectiveness is mixed, light therapy is thought to stimulate the sun’s rays that are missing during the winter months.
Pregnant women may also benefit from being outside as much as possible.
‘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,’ Dr Goyal said.
Melatonin is a hormone that regulates sleep, however, too much has been linked to insomnia and high blood pressure.
‘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,’ she added.
‘Likewise, early morning or late evening walks may be relaxing but would be less effective in increasing vitamin D exposure or suppressing melatonin.’
The study also found insomnia, stress and a poor relationship with their partner also increases a woman’s risk of postnatal depression.
A mother’s age and income has no effect, the research adds.
Postnatal depression affects more than one in 10 women within a year of giving birth in the US and UK.
Many experience the ‘baby blues’; when they feel down, teary and anxious within the first two weeks of giving birth.
But postnatal depression occurs when a woman feels persistently sad, tired and withdrawn, as well as her struggling to bond with her baby.
As many men may struggle with the condition as women, research suggests.
This comes after a study released earlier this year suggested singing helps women overcome postnatal depression.
New mothers who struggle with moderate-to-severe symptoms of the condition recover faster if they sing in a group, according to research by the Centre for Performance Science in London.