An expectant mother's smoking during pregnancy does not increase the likelihood that her child will later try smoking or become a regular smoker. Her pack-a-day smoking, however, doubles the risk that if her child does become a smoker, he or she will become addicted to tobacco, according to the first study to examine rates of tobacco addiction in adults who were prenatally exposed.
The study was led by Dr. Stephen L. Buka of the Harvard School of Public Health in Boston and cosponsored by the National Cancer Institute, the National Institute of Mental Health, The Robert Wood Johnson Foundation, and NIDA. Dr. Buka, together with Drs. Edmond D. Shenassa and Raymond Niaura, both of Brown Medical School in Providence, Rhode Island, collected data from 1,248 individuals aged 17 to 39. All the study subjects' mothers had participated in the Providence cohort of the National Collaborative Perinatal Project (NCPP) between 1959 and 1966. As part of the NCPP, pregnant women provided information about their smoking and gave blood samples for measuring nicotine levels.
Heavier Maternal Smoking During Pregnancy Increased Children's Odds of Nicotine Addiction as Adults. Children of women who smoked at least 20 cigarettes a day during pregnancy were more likely to become addicted to nicotine or progress from regular smoking to nicotine addiction as adults compared with children of women who smoked fewer than 20 cigarettes a day. Children of heavier smokers were no more likely to try smoking or to smoke regularly than children of lighter smokers.Among the men and women in the new study, 62 percent had smoked regularly and 45 percent met the medical criteria for tobacco dependence at some time in their lives. The criteria, as defined by DSM-III (Diagnostic and Statistical Manual of Mental Disorders, Revision III), include persistent, unsuccessful attempts to quit or control smoking, continued use despite smoking-related problems, and smoking to reduce withdrawal symptoms. Thirty-eight percent were born to mothers who did not smoke, 25.6 percent to mothers who smoked less than a pack a day, and 36.4 percent to mothers who smoked a pack or more per day at some point during pregnancy.
Among children who had smoked at least once, those whose mothers smoked up to a pack a day during pregnancy had a 20 percent higher, and those whose mothers smoked a pack a day or more had a 60 percent higher odds of having at some time been addicted to tobacco, compared with those whose mothers had not smoked. Among children who had at some time in their lives smoked daily for a month or more, those exposed in utero to a mother's pack-a-day smoking had double the odds of progressing to addiction.
"The evidence from this study, which reinforces the findings of experimental research with animals, is compelling," says Dr. Buka. "Early exposure to tobacco during pregnancy apparently affects the individual's response to cigarettes in later adolescence and adulthood."
The researchers' statistical analyses indicated that the associations between maternal smoking during pregnancy and offspring's future smoking were independent of socioeconomic status, maternal age at pregnancy, offspring sex, and offspring age at the time of the interview. What's left, then, is a biological factor. "The most likely hypothesis is that the toxins in cigarettes cross the placental barrier and interact with the genes that control cell differentiation, permanently altering cells' responsiveness in ways that increase vulnerability to tobacco addiction," Dr. Buka says.
The cross-generational impetus to tobacco addiction documented by the study is a serious national health concern. Almost half of women who smoke continue to do so when they become pregnant, says Dr. Buka. The smoking mothers-to-be constitute about 12 percent of women who give birth—a national potential for 500,000 prenatal exposures every year.
Maternal Tobacco Smoking During Pregnancy Did Not Affect Children's Odds of Marijuana Use as Adults. The finding that in utero exposure to tobacco did not affect later marijuana use indicates that the two drugs have different physiological pathways.The researchers also collected information about the study participants' marijuana abuse and found no tie to prenatal nicotine exposure. This suggests, the investigators say, that the "pathophysiological pathway" that promotes vulnerability to tobacco addiction among offspring differs from the pathway that leads to marijuana addiction.
The study confirms the need for energetic efforts to deter women from smoking, especially during pregnancy, says Dr. Kevin Conway, deputy chief of NIDA's Epidemiology Research Branch. Preventing smoking by pregnant women will improve nicotine addiction rates of the next generation. "This study highlights opportunities for physicians to intervene with mothers who smoke, for the health of themselves and their children," says Dr. Conway.
"Healthy-baby prenatal visits, labor and delivery, and postnatal-care visits are golden opportunities for providers to offer assistance to quit smoking and prevent relapse, thereby reducing the risk of children's progression to nicotine addiction," says study coauthor Dr. Niaura. "Health care providers must take advantage of every opportunity to ask, advise, and assist patients in efforts to quit smoking."
Source
- Buka, S.L.; Shenassa, E.D.; and Niaura, R. Elevated risk of tobacco dependence among offspring of mothers who smoked during pregnancy: A 30-year prospective study. American Journal of Psychiatry 160(11):1978-1984, 2003. [Abstract]