And do so as long before conception as possible. Perhaps years before. That's the conclusion of a new study that solves what has for years been a major puzzle about smoking and pregnancy: In a family where both parents smoke, how can doctors say which parent contributed to any medical problems in their children? Although further studies need to be done, the research by Bu-Tian Ji, M.D., who is also a Ph.D. candidate at the National Cancer Institute (NCI), suggests that men ought to quit smoking to protect their children from childhood cancer.
Dr. Ji went back home to his native China for his research because many more Chinese men smoke than women. "The smoking rate in Shanghai is about 60 percent among men," Dr. Ji says. "But traditionally, Chinese women don't smoke or drink." That means Dr. Ji and other researchers could easily zero in on large numbers of families where the dad smokes and mom doesn't.
Dr. Ji and his team of scientists studied 642 cases of cancer in Chinese children under the age of 15. At the same time they looked at another similar group with no cancer history, for comparison. They then confirmed the smoking histories of both parents to isolate what happens to the next generation when it's the man who uses tobacco.
What they found: Fathers who had smoked cigarettes at any point in their lives were 30 percent more likely to have a child with cancer than dads who had never smoked. "The length of time they smoked turned out to be more important than how many cigarettes they lit up per day," Dr. Ji says.
Dr. Ji's not sure why a man's past smoking habit seems to put his child at greater risk. "Even though sperm are made fresh in a man's body, we think maybe the environment in the reproductive system can continue to damage the sperm, or not protect it," he says. "But we don't yet have proof that this is what happens."
He acknowledges that his study doesn't exclude the possibility that the increase in childhood cancer is caused by secondhand smoke, inhaled by mothers-in-waiting. But other studies, of mothers who smoke, find no effect on the rate of cancer in their kids. That suggests that sperm, not secondhand smoke, could be the culprit. Another 1997 study, in England, backs up Dr. Ji's major finding. It links a father's smoking habit -- but not a mother's -- to an increased risk of cancer death among children in the U.K.
Dr. Ji looked only at the effects on childhood cancer, diagnosed annually in about 14 of every 100,000 U.S. children under age 15. Several other studies dating back to the 1960s reveal that fetuses and newborns are more likely to struggle for their lives if their fathers smoke. One showed that the overall death rate among infants of fathers who puff cigarettes was about 45 percent higher than the toll for babies sired by nonsmoking fathers. In addition, almost all studies of fathers who smoke find a greater incidence of birth defects in their children than in the offspring of fathers who don't light up.
More research is needed before anyone can be sure of the cancer connection and the overall risk of genetic damage to the next generation. Still, Dr. Ji's advice to men is not to wait until all the results are in. Stop smoking as long as possible before conception, he says. "I believe that it's best to quit at least five years before."