Prenatal nicotine exposure (such as from maternal smoking during pregnancy) has been hypothesized
to cause a so called programming effect, where epigenetic changes might result in a long-lasting
vulnerability to tobacco use and dependence, manifesting during adolescence or young adulthood.
However, previous observational studies show mixed results, perhaps because the association could
be influenced by a common genetic predisposition to tobacco use as well as by social factors
influencing both parental tobacco use during pregnancy and tobacco use in the offspring.
The aim of this thesis was to enhance knowledge about the association between prenatal exposure
to nicotine and tobacco use and tobacco dependence later in life.
Study I assessed the association between parental tobacco use during pregnancy and tobacco use
and dependence in adolescent offspring, based on 3,020 youths living in Stockholm County, who
were followed from age 11 to 18. Study II investigated the influence of maternal smoking during
pregnancy on tobacco use in adult offspring, based on 1,124 young adults, participating in the
Stockholm Public Health Survey in 2006 and 2010. The Swedish Sibling Health Cohort, which consists
of 1,538 sibling pairs, 19-27 years old and discordant for maternal smoking during pregnancy,
constituted the study population for Study III and IV. These studies assessed the influence of
prenatal exposure to maternal smoking on tobacco use (Study III) and dependence (Study IV) in
young adults, while taking genetic and environmental factors into account. Study IV was based on
two subsamples where both siblings were lifetime daily smokers (193 pairs) or snus users (173 pairs).
Results from this thesis showed that prenatal exposure to parental tobacco use was linked with a
higher risk of heavy tobacco use and dependence in adolescent girls (Study I). Maternal smoking
during pregnancy was associated with an increased risk of established and heavy snus use in young
adults (Study II). However, there was no association between maternal smoking during pregnancy and
tobacco use (Study III) or dependence (Study IV) when exposure-discordant siblings were compared.
In this thesis, prenatal nicotine exposure from parental tobacco use was not associated with tobacco
use or dependence in young adults. An association with heavy use and dependence in adolescent girls
cannot be excluded, but is more likely caused by residual confounding. These findings do not support
the hypothesis of an important programming effect caused by prenatal nicotine exposure. If such an
effect exists it is most likely weaker than the influence of genetic and early-environmental factors.
Instead, this thesis emphasizes the utmost importance of genetic and early-environmental influences on
the development of tobacco use and dependence
