Season of birth and substance abuse: findings from a large national sample

Season of birth is a putative etiological factor for several psychiatric illnesses. An excess of late winter and early spring births has been demonstrated repeatedly for schizophrenia, which has usually been interpreted as the result of prenatal or infant exposure to seasonally mediated "harmful effects," such as infectious diseases. This study determined whether the seasonal birth rates of substance abusers differed from those of unaffected control groups.

The 1992 National Longitudinal Alcohol Epidemiologic Survey, an interview-based study of 42,862 men and women, provided data to assess the association between quarter year of birth and lifetime diagnoses of substance abuse.

Logistic regression revealed decreases in winter births in men with histories of alcohol dependence. The significant interaction of sex with season of birth reflected an excess of fall births among male but not female alcoholics. In contrast, there was no evidence of seasonality of birth among alcohol abusers. Men and women with histories of illicit drug use had excesses of fall birth.

Birth rates of men with past or present alcohol dependence, and of men and women with histories of illicit drug use, implicated seasonal factors in the pathogenesis of substance abuse. The similar birth patterns of illicit drug users and male alcoholics suggest that they may share some common etiological factor, such as seasonal effects on environmental temperature, hormonal function, or susceptibility to viral infection during pregnancy or early infancy.