Smoking depletes vitamin C from mom, fetus.

In his later years, Nobel laureate Linus Pauling touted megadoses of vitamin C as a preventive medicine. He speculated that the vitamin prevents diseases ranging from the common cold to cancer. While conventional nutritional wisdom questions the benefits of such a regimen for everyone, new evidence suggests that pregnant smokers may do well to double their vitamin C intake.

A research team from Our Lady of Mercy Medical Center in New York followed a group of smoking and nonsmoking women through their pregnancies and reported its findings last week in San Francisco at the annual meeting of the American College of Obstetricians and Gynecologists.

The team found not only that the 226 smoking mothers had lower concentrations of vitamin C in their bloodstreams compared to the 174 nonsmoking participants, but that their fetuses got comparatively less vitamin C -- even when both groups of women had the same vitamin C concentrations.

"It really appears that the smokers may need more vitamin C and maybe more of other nutrients that we haven't identified yet to get the appropriate amount of nutrients across the placenta to the fetus," says study collaborator Lois Brustman.

Previous work had established that in order to neutralize the damaging free radicals found in tobacco smoke, smokers in general use more vitamin C than nonsmokers. In fact, the National Research Council included two-thirds more vitamin C for smokers in its 1989 Recommended Daily Allowance guidelines. However, the guidelines didn't address the needs of pregnant smokers.

The New York team followed the 400 women through their pregnancies and found striking differences in the amount of vitamin C in their bloodstreams. On average, the smokers had 15 percent less vitamin C than the nonsmokers.

Surprisingly, the smokers' bodies appeared to notice the deficit: Smokers consumed 30 percent more vitamin C. Team leader Kevin D. Reilly says the smoking mothers "appeared to be satisfying a biological craving to consume vitamin C--containing foods and juices," because the smokers didn't know that smoking specifically depletes vitamin C.

Because vitamin C needs increase substantially in pregnancy, Reilly's group speculated that the discrepancy between the amount of vitamin C consumed by pregnant smokers and the amount in their blood may result from the dual stresses of smoking and pregnancy.

Typically, newborns have twice the vitamin C concentration of their mothers. The New York team examined the concentrations of vitamin C in the mothers' bloodstreams and in blood from the infants' umbilical cords. While the newborns of nonsmoking mothers had twice as much vitamin C in their cord blood, the newborns of smokers had only 1.5 times as much as their mothers.

"This isn't just a case of less available vitamin C. We are looking at a potential problem with transport of vitamin C across the placenta," Brustman says. This, she adds, indicates that smoking mothers may need twice as much vitamin C as nonsmokers.

While the study is only preliminary, biochemist Balz Frei of Boston University Medical Center calls the finding "interesting" and "indicative of a transport problem, since the ratio between mother and infant is different."

Another result indicates problems with the placentas of smoking mothers. When the researchers looked at the three stages of labor, they discovered that the final stage, when the uterus expels the placenta, lasted nearly twice as long for the smokers. "This can be particularly dangerous, because the longer stage 3 is, the more a woman is likely to hemorrhage," Reilly says.

The team plans to study whether low vitamin C, which plays a role in connective tissue development, prolongs the final stage of labor.