Smoking while pregnant may leave your adult son more winded than his counterparts, a new Finnish study published Wednesday in BJOG suggests.

Studying the fitness records of more than 500 young Finnish men who entered the military in 2005, the authors were able to find a relatively small but real connection between the soldiers’ fitness levels and their mothers’ smoking history. Those whose mothers had smoked more than a cigarette a day during their pregnancy were more likely to report lower aerobic fitness than those whose mothers hadn’t, independent of other factors like the person’s own smoking habits or body mass index (BMI).

"It’s well established that smoking and breathing in second-hand smoke are harmful for both mother and baby. Our study adds to the existing evidence base of the negative and long-standing impacts of maternal smoking,” said lead author Dr. Maria Hagnäs from the University of Oulu, Finland, in a statement. “Women must receive advice and support to help them stop smoking during pregnancy, as well [as] guidance on how to maintain a healthy weight to minimize the risks to their unborn child.”

A Smoking Gun

In order to look back in time at the men’s maternal influences, Hagnäs and her colleagues turned to data from the Northern Finland Birth Cohort study, a long-running longitudinal study of expectant mothers and their offspring that ran first in 1966 and then in 1986. This meant the researchers could easily track down the 508 sons from the 1986 phase who joined the military around the age of 19, as well as cross-reference them with their mothers’ health status during pregnancy. All young Finnish men are conscripted to join either military or civilian service for a period of time once they’re above 18, with just under 80 percent choosing the military.  

One of the qualifications needed to join the Finnish military service involves taking the Cooper Test, which simply asks someone to run as far as they can for 12 minutes straight. Armed with these scores, as well as their muscle fitness index, the authors could make a comparison between the group of 59 men whose mothers had smoked during pregnancy and the group whose mothers hadn’t.

On average, the smoking group ran 2356 meters in 12 minutes (a smidge less than 1.5 miles), while the nonsmoking group ran 2537 meters (slightly over 1.5 miles). Though factors like the sons’ physical activity or smoking levels may account for some of this difference, the researchers still found an enduring association between worse fitness scores and maternal smoking alone. Conversely, although high prepregnancy maternal BMI and/or large weight gain during pregnancy was also associated with worse fitness for sons, that connection disappeared after the researchers took birth weight into consideration.

While untangling the exact influence that even something as harmful as cigarette smoke can have in the womb is a difficult task, this study is only the latest brick in the mortar demonstrating the long-lasting repecussions of smoking while pregnant. It’s already believed that maternal exposure to smoking contributes to lower birth weight, respiratory illness, and the risk of premature birth, among many other conditions.

“Stopping smoking is one of the most important things a pregnant woman can do to improve their baby’s health, growth and development, and this study demonstrates the negative effect smoking in pregnancy can have on a child’s long-term health too,” commented Dr. Geeta Kumar, chair of the Royal College of Obstetricians and Gynecologists Patient Information Committee, which is based in the United Kingdom. “It is important that women understand the risks of smoking in pregnancy and are aware of the support that is available to help them stop. Women who are unable to quit smoking should be encouraged to abstain during their pregnancy, use nicotine replacement therapy, or to reduce smoking as much as they can.”

Source: Hagnäs M, Cederberg H, Jokelainen J, et al. Association of maternal smoking during pregnancy with aerobic fitness of offspring in young adulthood: a prospective cohort study. BCOG. 2015.