Women are more affected by the changes in the season making them more at risk “winter blues” than men, a new study found.
Shorter days and colder temperatures such as a dip in summer triggers depression in women.
And as the days got longer they felt more tired then men.
Seasonal affective disorder (SAD), also known as “winter depression” because symptoms are more severe, comes and goes in a seasonal pattern.
Those affected feel lethargic, have a persistent low mood, a loss of pleasure or interest in normal everyday activities known as anhedonia, irritability and feelings of despair, guilt and worthlessness.
They often begin in the autumn as the days start getting shorter and become most severe during December, January and February although they improve and disappear in the spring and summer.
An estimated three per cent of the population suffer from SAD.
Women more likely to be affected than men
Now a new study by the University of Glasgow found that women, but not men, experience seasonal changes in their mood across the year, including more depressive symptoms in winter.
Their symptoms peaked in winter and there was a link between shorter and coder days and greater depressive symptoms.
But as days lengthened they also reported feeling more tired.
These triggers were independent of social and lifestyle factors, such as smoking, drinking and physical activity.
The study involved a cross-sectional analysis of more than 150,000 middle aged adults taking part in the UK Biobank cohort.
It analysed data to assess evidence of seasonal variation by scoring ‘total depressive symptoms’, plus symptoms of low mood, anhedonia, tenseness and tiredness.
Associations between depressive symptoms and day length and average outdoor temperatures were also assessed.
Professor of Psychiatry Daniel Smith from the University’s Institute of Health and Wellbeing said: “In this study we report evidence of seasonality of depressive symptoms in women but not men within a large sample of middle-aged adults in the UK.
“Among women, total depressive symptom score and anhedonia peaked in the winter months.
“Longer day length was associated with reduced reporting of low mood and anhedonia and with increased reporting of tiredness in women, independent of demographic and lifestyle confounders of age, ethnicity, deprivation, UK Biobank centre, typical physical activity, smoking status and alcohol intake.
“The association of tiredness with day length was also independent of mean outdoor temperature, but the remaining associations did not survive correction for temperature and time/day of assessment, suggesting that environmental factors other than day length may contribute to seasonal fluctuations in mood.”
He added the “analysis did not reveal a seasonal pattern of depressive symptoms in men, but men showed similar associations of anhedonia and tiredness scores with day length to women.”
He explained the findings confirmed previous studies that linked a higher prevalence of depression with seasonal pattern among women with them more likely to be admitted for depression over winter than men, especially the further north they live.
He said: “Temperature was a significant predictor of low mood and anhedonia scores in women independent of day length and the other demographic/lifestyle confounders.
“Together these findings suggest that temperature may have a greater influence on seasonal variation in mood than day length, although it remains possible that shared variance between both day length and temperature contributes to fluctuations in depressive symptoms.
“Consistent with the role of temperature, an earlier study found that colder temperatures within summer were associated with increased prescriptions of antidepressant medication in Sweden.”
Prof Smith concluded: “This very large, population-based study provides evidence of seasonal variations in depressive symptoms which appear to be more pronounced in women than in men.”
Sex-specific biological mechanism
“We don’t yet fully understand why this should be the case, but it was interesting that the changes were independent of social and lifestyle factors, perhaps suggesting a sex-specific biological mechanism,” said Prof Smith.
“Clearly, this is a complex but important area which requires further study.
“In summary, we provide evidence that feelings of depressive symptoms, particularly anhedonia, are more common during winter months for women, consistent with previous research.
“Further, environmental factors including day length and outdoor temperature are important predictors of depressive symptoms, although future studies should also consider the role of time spent outdoors, time spent in natural light, and latitude.
“These findings have important implications for the provision of healthcare around the world.
“Subclinical depressive symptoms are associated with increased risk of developing major depression and with reduced wellbeing, but are often under-recognised and
“Clinicians should be more aware of these differences in the experience of depressive symptoms between women and men across the seasons in order to facilitate their recognition and appropriate treatment.”
The study was published in the Journal of Affective Disorders.