A baby whose mother smoked during pregnancy will age more quickly

We know: exposure to tobacco during pregnancy is harmful to the fetus. Prematurity, low birth weight or even, as you grow up, an increased risk of respiratory problems, diabetes, cancer or even a greater susceptibility to addiction. The list of harms of tobacco for the unborn child is long… and continues to grow. Because prenatal exposure to tobacco also promotes the biological aging of certain organs. This is the conclusion of a Chinese study published in Science Advances. In other words, people exposed to tobacco in the womb and/or in childhood are more likely to suffer early from diseases that normally appear in the elderly.

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In this study, researchers from Huazhong University of Science and Technology (Wuhan) retrieved the biological data of more than 270,000 participants, 80,000 of whom were exposed to tobacco in utero, from the British Biobank database. They were specifically interested in blood markers known to vary during aging (cholesterol, creatinine and glucose levels, immune cells, etc.), as well as the size of telomeres. “Telomeres are structures composed of DNA sequences located at the ends of chromosomes, and responsible for protecting their integrity. In all humans, they shorten with age but this process can be more or less rapid,” explains Eric Gilson, professor at the Faculty of Medicine of Nice and researcher at the Institute for Research on Cancer and Aging (IRCAN ).

From this data, they were able to estimate and compare the actual age of individuals' bodies, depending on whether or not they were exposed to tobacco in utero. This is called “biological” age – independent of their actual age or “chronological age” (the number of years since their birth). This estimate of biological age was based on two statistical approaches: the calculation of the KDM-BA score (Klemera-Doubal Method for Biological Age), an algorithm which takes into account several biomarkers (blood, genetics, etc.), and the PhenoAge score, an approach based on clinical measurements such as blood pressure, cholesterol level, weight, height, etc.

Result: if we compare two 40-year-old people, the body of the one exposed to cigarette smoke at an early age ages more quickly. In detail, people exposed in utero were older by 0.26 KDM-BA years and 0.49 PhenoAge years compared to individuals of the same age who had not undergone maternal smoking, and their telomeres were on average longer. short of 5.34%. This acceleration of aging was even more pronounced for people exposed during childhood (or even having started smoking during adolescence): their bodies were on average older by 0.88 KDM-BA years and 2.51 PhenoAge years and their telomeres shorter by 10.53%. But first place on the podium goes to individuals exposed both in utero and during childhood, who were 1.13 years KDM-BA and 2.89 years PhenoAge older than their actual age.

Also read: Why don't all our organs age at the same speed?

“We suspected the harmful effects of childhood smoking on aging, but this is one of the first studies to estimate it with a robust approach which made it possible to eliminate the effect of confounding factors such as genetic predisposition to early aging », underlines Professor Gilson. However, the mechanisms by which tobacco affects aging remain unclear. Toxic substances (heavy metals, tar, carbon monoxide, etc.) are the first to be blamed because they are capable of crossing the placental barrier and inducing oxidative stress. “These toxic compounds produce reactive oxygen species (ROS) that can damage DNA, accelerate telomere shortening, and contribute to cellular senescence, a state where cells remain alive but stop functioning optimally, while promoting chronic inflammation of the affected organs,” underlines Professor Gilson.

“We knew that smoking was associated with cardiovascular signs of aging in smokers, including the appearance of fatty plaques (atheroma) in the arteries, or even hypertension,” explains Tripti Rastogi, doctoral student at the center. multi-thematic clinical investigation at the Nancy University Hospital. “The novelty with this study is the demonstration of signs of aging in people exposed prenatally, raising fears of an early cardiovascular risk for these victims of smoking.”

While waiting to better understand the underlying mechanisms, the authors hope that these results will offer a new strong argument for prevention initiatives. “Contrary to popular belief, it is the smoke which is toxic and not the nicotine, which is the addictive substance,” recalls Dr Marion Adler, tobacco specialist at Paris hospitals. It is therefore preferable for pregnant women to take the dose of nicotine they need in the form of nicotine substitutes (patches, gum, etc.), rather than exposing themselves and their baby to smoke, to be able to stop the 'tobacco intoxication as quickly as possible and without suffering from withdrawal'.