Nutrition During Pregnancy Part I: Weight Gain, Part II: Nutrient Supplements (1990) / Chapter Skim
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18 Water-Soluble Vitamins
18 Water-Soluble Vitamins
Pages 351-379
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From page 351... ...
by women of childbearing age is generally reported to be lower than that of other water-soluble vitamins. Thus, the subcommittee reviewed evidence regarding the importance of vitamin B6 and folate in pregnant women, the estimated need for these vitamins, and the usual dietary intakes as a basis for its recommendations on supplementation.
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From page 352... ...
, the physiologically active form of the vitamin, is a coenyme in over 100 known reactions involved primarily in amino acid metabolism. PLP-containing enzymes include aminotransferases, which are essential to the synthesis of nonessential amino acids, and decarboxylases, which are needed in the formation of histamine, serotonin, dopamine, and y-aminobutyric acid.
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The most substantial decrease in plasma PLP levels is found between the fourth and eighth months of gestation, paralleling the period of most intensive growth of the
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From page 354... ...
. Plasma PLP, which has been studied extensively, has been reported to be an indicator of vitamin B6 body stores, whereas pyridoxic acid has been said to reflect intake (Leklem and Reynolds, 1988; Shane and Contractor, 1980; van den Berg, 1988~.
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Abnormal results from a combination of two or more laboratory tests, e.g., decreased activity of vitamin B6-dependent enzymes coupled with high activity coefficients, are considered more indicative of vitamin B6 inadequacy than is one abnormal measurement. Usual Intakes As shown in Chapter 13, 1bble 13-2, dietary intakes of vitamin B6 by pregnant women in the United States have often been reported to be lower than the RDA (NRC, 1989~.
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The active transport of vitamin B6 from maternal to fetal blood against a concentration gradient in the placenta lessens the effects of maternal vitamin B6 inadequacy on the newborn, but it also could result in abnormally high levels in the fetus if pregnant women are given enough supplemental pyridoxine to increase their plasma PLP levels to those of nonpregnant women. Shane and Contractor (1975)
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From page 359... ...
Toxicity There are few data on the safety of pyridoxine supplementation during human pregnancy. Oral doses of pyridoxine greater than 500 mg/day for prolonged periods can result in the development of sensory neuropathy in nonpregnant adults (Cohen and Bendich, 1986)
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From page 360... ...
was associated with significantly lower maternal and umbilical cord serum vitamin B6 levels than those in women who took no oral contraceptives, and evidence indicates that their vitamin B6 reserves may be decreased in early pregnancy (Roepke and Kirksey, 1979b)
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From page 361... ...
successfully treated macrocytic anemia in pregnant women with yeast extract; the active substance was later identified as folate. The etiologic role of folate deficiency in megaloblastic anemia of pregnancy and the efficacy of folate therapy in the treatment of this disease are now well established.
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From page 362... ...
Adverse pregnancy outcomes have been linked with impaired folate status in disadvantaged populations in which folate deficiency and adverse birth outcomes are relatively common. In Johannesburg, South Africa, for example, an oral 500-,ug/day supplement of folic acid was associated with a 50% reduction in small-for-gestational-age newborns among Bantu women consuming a low-folate diet; a similar eRect was not observed among white women, who consumed more fruits and vegetables (Baumslag et al., 1970~.
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From page 363... ...
A dietary folate intake of 3 ,ug/kg of body weight has been reported to support adequate liver folate stores and to provide for a margin of safety in nonpregnant women (NRC, 1989; Reisenauer and Halsted, 1987~. ~ determine more precisely the magnitude of the increased folate need during pregnancy, a more complete understanding of cellular folate homeostasis and tissue folate requirements is required (Reisenauer and Halsted, 1987~.
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From page 364... ...
showed that folic acid supplements produced a peak increase in reticulocytes from O up to 5 to logo of circulating red blood cells in most folate-deficient patients within 5 to 10 days after treatment. Usual Intake Folates are present in a variety of foods and occur in especially high levels in liver, fortified or whole grain breads and cereals, dried peas and beans, leafy vegetables, fruit (Subar et al, 1989)
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diets is approximately one-half to two-thirds that of supplemental folio acid ingested separately from food (Sauberlich et al., 1987~. Estimates of dietary folate for population subgroups in the United States are limited.
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Low acute and chronic toxicity has been observed in nonpregnant adults. Folic acid is readily excreted in urine.
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Substantial amounts of thiamin, riboflavin, and niacin are provided by enriched and fortified grain and bakery products. Microfloral synthesis of pantothenic acid and biotin augment the dietary intake of those vitamins.
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The decrease has been attributed largely to hormonal adjustments and blood volume expansion during pregnancy rather than to the increased vitamin C demands by maternal and fetal tissues. Increased intake of vitamin C may prevent or mitigate the fall in plasma levels (Vobecky et al., 1974~.
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Other Considerations Some subpopulations follow practices that increase their need for, or result in low dietary intake of, vitamin C These include users of street drugs and cigarettes (see Chapter 20)
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Niacin is present in all cells and participates in several metabolic processes, including glycolysis, fatty acid metabolism, and tissue respiration. Because of this involvement of thiamin, riboflavin, and niacin in energy metabolism, these vitamins are needed during pregnancy in amounts proportional to the increased energy requirements (Table 18-1~.
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From page 371... ...
Dosage Range and Toxicity In nonpregnant humans, no toxic effects have been reported for thiamin, riboflavin, and niacin following long-term high-dose (100 to 200 mg/day) oral supplements of the vitamins, except for some gastric upset.
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From page 372... ...
The vitamin is widely distributed in foods, especially in meats, whole-grain cereals, nuts, and legumes. Synthesis of pantothenic acid by intestinal bacteria possibly supplements the dietary intake of this vitamin.
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From page 373... ...
For complete vegetarians, a daily vitamin B:2 supplement of 2.0 fig is recommended. · Special attention should be given to improving the diet of and administering supplements to pregnant adolescents, women bearing more than one fetus, users of cigarettes or street drugs, heavy users of alcohol, and pregnant women at nutritional risk because of poor nutritional knowledge or insufficient financial resources to purchase adequate food.
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1970. Reduction of incidence of prematurity by folic acid supplementation in pregnancy.
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1972. Pyridoxal phosphate and folic acid concentration in blood and erythrocyte aspartate aminotransferase activity during pregnancy.
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1975. Effect of folio acid supplement on birth weights of infants.
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1987. Recommended dietary intakes (RDI)
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1975. Relationships of ascorbic acid to pregnancy and oral contraceptive steroids.
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From page 379... ...
86-1. Nutrition Monitoring Division, Human Nutrition Information Service, U.S.
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