Season of birth is different in Inuit suicide victims born into Traditional than into Modern Lifestyle: a register study from Greenland

BACKGROUND: There is growing evidence that living conditions at birth play a role in medical conditions later in life. Population-based studies from the Northern Hemisphere have shown that persons born in the spring or summer are at greater risk of committing suicide. A statistical correlation with light availability at birth has been observed in past research, but the cause remains unknown. Greenland is one of the most extreme of natural human habitats with regard to seasonal changes in light. The combination of rapid social changes and reliable population statistics offers a unique opportunity to make comparisons between persons born into a Traditional Lifestyle and those born into a Modern Lifestyle. The aim of this work was to assess whether season of birth differed between suicide victims born into an old or into a modern lifestyle. METHODS: Official population and mortality registers were used. Suicide victims born (1903–1950) into the Traditional Lifestyle were compared with those born into the Modern Lifestyle (1961–1980). Rayleigh’s test for circular distributions was used to assess the season of birth in suicide victims. Data regarding season of birth in the general population were collected. RESULTS: Persons born in March-June in the Traditional Lifestyle were much less likely to commit suicide than those born during other periods of the year. This is contrary to the findings of other studies. The seasonal differences had disappeared for those born into the Modern Lifestyle. The suicide rate increased from very low rates to about 140 suicides/100 000 person-years in the 1980s. CONCLUSIONS: The reason behind a variation in season of birth in suicide victims born into the old lifestyle is unknown. It is also unknown why the seasonal difference had disappeared with modern lifestyle. Possible influence of artificial light, nutrition, microbiota and seasonal infections are discussed. The underlying causes behind suicides may be different in traditional and modern Greenland.