BACKGROUND: Early midlife individuals (ages 30-40) experience demographic shifts that may influence the remainder of adult life. Although new or persistent alcohol misuse is common during this period, early midlife is understudied in alcohol use literature. We examined the heritability of alcohol misuse; the associations between alcohol misuse and sociodemographic factors, physical health, and well-being; and whether these associations were robust in cotwin comparisons.

METHODS: Participants were 1446 Finnish twin pairs and 748 nonpaired Finnish twins with mean age 34 years. The alcohol misuse index was a composite measure of frequency of use, intoxication, heavy episodic drinking, and alcohol problems assessed with the Malmö-modified Michigan Alcoholism Screening Test and the Rutgers Alcohol Problem Index. Early midlife correlates included relationship status and length, family formation, unemployment status, education level, self-rated health, pain, sleeping difficulties, life satisfaction, psychological health, and other substance use. We employed a sex-limitation model to estimate early midlife heritability. Linear and fixed effects regression models were used for individual and cotwin comparison analyses, respectively.

RESULTS: Additive genetic (A) and unique environmental (E) components of alcohol misuse variance differed across sex (Females: A = 62%, E = 38%; Males: A = 49%, E = 51%). In individual-based analyses, higher scores on the alcohol misuse index were associated with lower relationship stability, financial situation, education level, self-rated health, physical fitness, life satisfaction and psychological health, and higher self-reported pain, sleep difficulties, unemployment rates and other substance use (R = 0.008-0.12). Associations remained significant in cotwin comparison analyses (R = 0.004-0.10) except for financial situation and education level.

CONCLUSIONS: There is evidence of sex differences in the etiological factors that influence early midlife drinking. After controlling for confounding familial factors, associations between alcohol misuse and poorer early midlife functioning largely remained, suggesting that alcohol misuse may play a role in poorer functioning across several outcomes.