August 5, 2025, 8:43 am | Read time: 6 minutes
Does the month of birth affect our mental health in adulthood? A new study explored this question–with a remarkable result: Men born in the summer showed more frequent depressive symptoms. No similar correlation was found in women. What early environmental factors might have to do with this–and why the topic is important not only for researchers but also for health policy–read here.
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What Was Studied and Why?
Previous studies have suggested that the month of birth can influence the risk of certain diseases–such as schizophrenia or multiple sclerosis.1 The background: During pregnancy, the body is particularly sensitive to external influences like sunlight, nutrition, or infections. These so-called seasonal environmental factors change throughout the year–and could thus also affect the development of the unborn child.
Less researched is whether common mental issues like depression or anxiety disorders are related to the season of birth. The existing results are inconsistent. The study examined whether there could be a connection between birth month and depression in adulthood. A Canadian research team led by Arshdeep Kaur sought to find out if there is a link between birth timing and later mental symptoms–and whether this might depend on gender.
Conducting the Study
Between January and March 2024, 303 adults participated in an online survey. They were on average 26 years old, and 65 percent of them were women. Participants were recruited through social media, student networks, and postings at universities in the Vancouver area (Canada).
To assess the participants’ mental stress, the researchers used two globally recognized questionnaires:
- PHQ-9 (Patient Health Questionnaire-9):
This test measures depressive symptoms based on nine typical complaints–such as lack of drive, sleep disturbances, concentration problems, or feelings of worthlessness. The more frequently the symptoms occur, the higher the score. From ten out of 27 possible points, there is an increased risk of a depressive disorder. - GAD-7 (Generalized Anxiety Disorder-7):
This questionnaire captures seven symptoms that indicate a generalized anxiety disorder–such as constant worries, nervousness, or physical restlessness. Here too, from ten points on the scale, the risk for a treatable anxiety disorder is increased.
Additionally, information on age, income, education level, ethnic background, and relationship status was collected. The birth months were divided into four seasons: spring, summer, fall, and winter. To avoid distortions, the statistical analysis also considered differences in residence (by geographic latitude), income, and age. A possible influence of birth month and depression was examined with a gender-specific focus.
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Higher Depression Scores in Men Born in Summer
The mental stress in the sample was notably high overall:
- 84 percent of participants reached scores indicating depressive symptoms,
- 66 percent showed signs of an anxiety disorder.
Younger participants and those with lower incomes were particularly affected. Women also reported stronger symptoms on average than men.
However, the central question of the study was whether the time of birth influences the risk of mental illnesses–and whether this effect is differently pronounced in men and women.
The Central Result
- Men born in the summer had higher depression scores on average than men with other birth months.
- No comparable correlation was found in women.
An interaction effect between gender and birth time was found–a term from statistics that describes two characteristics having a joint influence. In this case: Gender and season of birth together influence the risk of depressive symptoms. The measured statistical value–the so-called p-value–was 0.054.
What Does This Mean?
In science, a result is considered “statistically significant” if the p-value is below 0.05. This means: It is very unlikely that the observed difference is due to chance alone. In this study, the value was just above this threshold–at 0.054. This means: The correlation is not clear, but close enough to the significance threshold to be considered a possible indication of a real effect. Such results are referred to as “marginally significant.”
For anxiety symptoms, however, no connection with the birth time could be established–neither in men nor in women. Characteristics such as ethnic affiliation, educational level, or professional status also showed no clear influence.
Season and Gender Apparently Important Regarding Depression Risk
The study provides indications that the season of birth–as an indirect hint at environmental conditions during pregnancy–could have long-term effects on mental health. Particularly interesting: This effect seems to occur only in men.
How Could This Be Explained?
Previous investigations show that the time of birth influences the growth of certain brain regions–such as the so-called superior temporal lobe, which is responsible for emotions, social perception, and stimulus processing.2 Notably: This brain region seems to develop differently in men and women depending on the season. This could explain why depressive symptoms occur gender-specifically depending on the birth time.
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Study Classification and Possible Limitations
As with any scientific investigation, there are limitations here:
- The sample was relatively small (303 people) and consisted mainly of young adults. Almost 80 percent of participants were between 18 and 29 years old, nearly 40 percent were students, and more than half were female. Therefore, the results cannot be easily generalized to the entire population.
- This is a so-called cross-sectional study, a snapshot. This means: Connections were observed, but no statements about causes and effects were made. Whether the season of birth actually promotes depression–or whether other influences are involved–remains open.
- The survey was conducted only in the winter months (February and March). This could have affected the self-assessment of mental stress–although the researchers methodically considered this effect by focusing on the birth month rather than the current mood.
Conclusion
The study shows: Men born in the summer may have an increased risk of depressive symptoms in adulthood. The available data suggest that the birth month could increase the risk of depression–but not in women. This effect was not detectable in women. For anxiety symptoms, no connection with the season of birth was found.
Even though the results must be interpreted cautiously, they suggest that seasonal environmental factors during pregnancy could play a role in mental health–and these effects may depend on gender. Future research should further investigate this connection in larger, more diverse samples.