Cigarette smoking, alcohol use and adverse pregnancy outcomes: implications for micronutrient supplementation.

This literature review examines whether smoking or alcohol use during pregnancy increases maternal micronutrient requirements and whether smoking or alcohol use interacts with micronutrient deficiencies to affect pregnancy outcomes. Studies suggest that vitamin C requirements increase for pregnant smokers. Studies also indicate that beta-carotene, vitamin B-12, vitamin B-6 and folate concentrations appear lower in pregnant smokers than in pregnant nonsmokers, although it is unclear whether lower serum concentrations are due to increased requirements, lower dietary or supplement intakes or other factors. Experimental animal studies suggest that iron supplementation partially ameliorates impaired fetal growth caused by cadmium, a heavy metal inhaled from cigarette smoke, but studies in humans have not substantiated cadmium's effect on fetal growth. Animal studies also suggest chronic alcohol consumption at levels of 20-50% of energy intake during pregnancy may mobilize fetal vitamin A concentration from the liver and result in increases in vitamin A in fetal organs and subsequent defects. Evidence is lacking, however, on whether zinc metabolism is altered by alcohol intake during pregnancy. Health care practitioners should consider increasing nutrient levels in pregnant women who do not meet the Recommended Dietary Allowances through their diet. Future studies that examine the nutrient levels of women exposed to cigarette smoke and alcohol should control for dietary intake. In addition, randomized controlled studies of the health impact of micronutrient supplementation in pregnant women should consider stratification by exposure to cigarette smoke and alcohol use.