The effect of maternal smoking on the relationship between maternal and fetal zinc status and infant birth weight.

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Abstract
We have previously reported a trapping of zinc in the placenta directly related to circulating cadmium that comes from cigarette smoke. The purpose of this study was to examine in detail the effect of smoking on (a) the relationship between maternal and fetal zinc status and (b) the relationship between zinc status and birth weight. One hundred and eighteen smokers and 172 nonsmokers without any medical complications during pregnancy were studied. Atomic absorption spectroscopy was used to assess zinc status in maternal and cord vein plasma and red blood cells. Plasma alkaline phosphatase was also determined as an index of zinc status. Thiocyanate was used as an index of smoking status. The data were analyzed using univariate correlations and repeated measures analysis of variance. Infants of smokers had a statistically significant decrease in plasma zinc (5%), alkaline phosphatase (13%), and in cord vein RBC zinc (12%). Furthermore, the results showed an altered relationship between maternal and fetal indices of zinc status and zinc status and birth weight due to maternal smoking. The infant of the nonsmoking mother appears to be able to maintain adequate zinc status due to depletion of maternal zinc. However, it appears that the infant of the smoking mother may be marginally zinc deficient. These findings support studies of zinc supplementation in the pregnancy complicated by smoking. The effect of cigarette smoking on, 1st, the relationship between maternal and fetal zinc status, and 2nd, the relationship between zinc status and birthweight was investigated in 118 smokers and 172 nonsmoking controls. Zinc status in maternal and cord vein plasma and red blood cells was assessed by means of atomic absorption spectroscopy. Plasma alkaline phosphatase was also used as an index of zinc status, while thiocyanate was used as an index of smoking status. The data indicated an altered relationship between zinc status in mother and fetus and an altered relationship between plasma and cord vein red blood cell zinc and birthweight due to maternal smoking during normal pregnancy. In smokers, there were significant positive correlations between maternal and cord vein heat labile alkaline phosphatase, between maternal and cord vein red blood cell zinc, between maternal and fetal plasma zinc, and a significant negative correlation was found between maternal plasma zinc and fetal red blood cell zinc. At each birthweight interval, infants of nonsmokers have more red blood cell zinc in their cord blood than their mothers. Also found was an inverse relationship between maternal plasma zinc and birthweight in smokers, suggesting that zinc is unable to reach the smoker's fetus. In contrast, infants of nonsmokers appear to be able to maintain adequate zinc status due to depletion of maternal zinc. It is possible that the inability of zinc to cross the placenta in cases of maternal smoking can be partially ameliorated by a more adequate maternal zinc status. Thus, zinc supplementation in smokers is worthy of consideration during pregnancy.

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