Month of birth and mood seasonality: A comparison between countries in the northern and southern hemispheres

Abstract

Aims A previous study has reported a significant month‐of‐birth effect on mood seasonality in the northern hemisphere. Higher mood seasonality was observed for university students born during spring or summer months (long photoperiod) compared to those born during autumn or winter months (short photoperiod). The aim of this study was to test the hypothesized photoperiod effect by comparing the correlation between month of birth and mood seasonality in two countries located at the opposite poles of the terrestrial globe: Italy (northern hemisphere) and New Zealand (southern hemisphere). On the basis of the photoperiod‐at‐birth hypothesis, we expected to find higher mood seasonality among individuals born in months with longer photoperiods in both countries. Methods The Seasonal Pattern Assessment Questionnaire was administered to 1514 young adults (1088 women, 426 men; 1027 Italians, 487 New Zealanders), with ages ranging from 18 to 34 years. The Global Seasonality Score, which is a measure of mood seasonality, was calculated from the Seasonal Pattern Assessment Questionnaire. Results A significant overall month‐of‐birth effect was observed on the Global Seasonality Score, but only for men. Men born in April and August (corresponding in Italy to a long photoperiod, in New Zealand to a short photoperiod) had higher mood seasonality than those born in February, regardless of country. Conclusions A significant month‐of‐birth effect was found on mood seasonality, but results do not support the hypothesis based on the photoperiod effect.

Female gender but not season of birth is associated with mood seasonality in a near-equatorial Brazilian city

“…In line with previous findings 9,11 , we observed a main effect for gender on mood seasonality. These congruent findings indicate that women tend to experience greater mood seasonality than men, and that the current treatments for sufferers of mood disorders (such as SAD) may have differing effects for men and women.…”

“…A significant overall month of birth effect was observed only for male participants (regardless of country), with those born in April or August having higher mood seasonality than those born in February. This and other studies have also observed significant gender differences, with female participants showing higher mood seasonality than males 9,11 . Due to the geographic location of the findings reviewed above, it would be necessary to test the robustness of these results using more samples from countries in the Sou thern Hemisphere.…”

“…Higher mood seasonality has been observed in the Northern Hemisphere for individuals born during spring/summer months compared to those born during autumn/winter months 9,10 . The effect of month of birth on mood was also observed in a recent study involving participants from both hemispheres 11 . The present study contributed to this literature by examining the influence of season of birth on mood in another sample from a country in the Southern Hemisphere (Brazil).…”

“…While higher mood seasonality was observed for university students born during spring/summer months compared to those born during autumn/winter months in both Italy and Spain 9 , higher mood seasonality for New Zealand participants was observed for those born during a winter month (August) compared to a summer month (February) 11 . These patterns of findings may be due to a difference between participants born in the Northern and Southern Hemispheres.…”

“…The same pattern of findings was observed in another study with a large sample of Italians in late childhood and adolescence (age ranging from 10 to 17 years), indicating that the significant effect of season of birth on mood seasonality is already present at a young age 10 . Expanding these initial findings, a more recent study compared the influence of season of birth on mood among participants located in the Northern (Italy) and Southern Hemispheres (New Zealand) 11 . A significant overall month of birth effect was observed only for male participants (regardless of country), with those born in April or August having higher mood seasonality than those born in February.…”