Abstract
BackgroundThe comparison of traits in twins from opposite-sex (OS) and same-sex (SS) dizygotic twin pairs is considered a proxy measure of prenatal hormone exposure. To examine possible prenatal hormonal influences on anthropometric traits, we compared mean height, body mass index (BMI), and the prevalence of being overweight or obese between men and women from OS and SS dizygotic twin pairs.MethodsThe data were derived from the COllaborative project of Development of Anthropometrical measures in Twins (CODATwins) database, and included 68,494 SS and 53,808 OS dizygotic twin individuals above the age of 20 years from 31 twin cohorts representing 19 countries. Zygosity was determined by questionnaires or DNA genotyping depending on the study. Multiple regression and logistic regression models adjusted for cohort, age, and birth year with the twin type as a predictor were carried out to compare height and BMI in twins from OS pairs with those from SS pairs and to calculate the adjusted odds ratios and 95% confidence intervals for being overweight or obese.ResultsOS females were, on average, 0.31 cm (95% confidence interval (CI) 0.20, 0.41) taller than SS females. OS males were also, on average, taller than SS males, but this difference was only 0.14 cm (95% CI 0.02, 0.27). Mean BMI and the prevalence of overweight or obesity did not differ between males and females from SS and OS twin pairs. The statistically significant differences between OS and SS twins for height were small and appeared to reflect our large sample size rather than meaningful differences of public health relevance.ConclusionsWe found no evidence to support the hypothesis that prenatal hormonal exposure or postnatal socialization (i.e., having grown up with a twin of the opposite sex) has a major impact on height and BMI in adulthood.
Highlights
The comparison of traits in twins from opposite-sex (OS) and same-sex (SS) dizygotic twin pairs is considered a proxy measure of prenatal hormone exposure
OS males were on average, taller than SS males, but this difference was only 0.14 cm
Mean body mass index (BMI) and the prevalence of overweight or obesity did not differ between males and females from SS and OS twin pairs
Summary
The comparison of traits in twins from opposite-sex (OS) and same-sex (SS) dizygotic twin pairs is considered a proxy measure of prenatal hormone exposure. Whether an analogous effect exists in humans is uncertain; it has been postulated that twins influence each other hormonally during prenatal life because they share their intrauterine environment [4]. This is called the twin testosterone transfer (TTT) hypothesis. Support for the TTT hypothesis comes from previous twin studies showing that females from opposite-sex (OS) twin pairs express more male-typical characteristics (i.e., are masculinized) in a variety of sexually dimorphic traits. Having grown up with a sibling of the same sex versus a sibling of the opposite sex is likely to result in different social learning experiences and has been linked to sex-typed behavior; for example, boys with older brothers and girls with older sisters have been found to be more sex typed than children from opposite-sex sibling dyads [8]
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