Background: Exposure to tobacco smoking prenatally is a risk factor for reduced semen quality, but whether the exposure has adverse effects on reproductive hormones, pubertal development or adult BMI remain largely unexplored. The aim of this study was to investigate the associations between these factors while controlling for the effects of current smoking in young adulthood.
Methods: This cross-sectional study (1996-2006) included 3486 Danish men (median age: 19 years), participating in a semen-quality study. Data were obtained from questionnaires, physical examinations, semen analyses and assessments of reproductive hormones. The main outcome measures were markers of pubertal onset, BMI, reproductive hormones and semen variables.
Results: Maternal smoking during pregnancy was associated with earlier onset of puberty (e.g. early pubic hair development in 25.2 versus 18.9% of unexposed subjects), lower final adult height (median: 1.80 versus 1.82 cm), higher BMI (22.9 versus 22.4), smaller testicles (14.0 versus 14.5 ml), lower total sperm counts (119 versus 150 million), reduced spermatogenesis-related hormones (e.g. inhibin-B/FSH 66 versus 73 pg/mU) and higher calculated free testosterone (free-T, 2.38 versus 2.33 nmol/l). If not exposed prenatally, men's own smoking was associated with increased total testosterone but unchanged free-T. For smokers who had been exposed prenatally, total testosterone was increased but free-T was reduced (2.30 versus 2.38 nmol/l, P = 0.003) due to higher levels of sex hormone-binding globulin.
Conclusions: Prenatal exposure to tobacco may lead to faster pubertal development possibly caused by a higher free-T, and to higher adult BMI and impairment of testicular function. The findings may not be clinical relevant for the individual but are of public health importance, and add to the knowledge of effects of tobacco smoking.