Nutrition During Pregnancy Part I: Weight Gain, Part II: Nutrient Supplements (1990) / Chapter Skim
Currently Skimming:
16 Calcium, Vitamin D, and Magnesium
16 Calcium, Vitamin D, and Magnesium
Pages 318-335
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 318... ...
, and phosphorus is not ordinarily contained in multivitaminmineral supplements. CALCIUM Metabolism Several changes in calcium metabolism associated with pregnancy facilitate the transfer of calcium from mother to fetus while protecting calcium levels in maternal serum and bone.
|
From page 319... ...
A relatively new immunoradiometric assay that is highly specific for the intact, and presumably biologically active, form of PTH indicated that the mean serum PTH level in 81 pregnant women was 14.4 ~ 6.3 compared with 24.8 it 9.0 (standard deviation) ng/ml in 11 nonpregnant women (Davis et al., 1988)
|
From page 320... ...
Interpretation of these balance data is difficult due to the different levels of calcium intake, stage of pregnancy, and duration of the various studies. Maternal Bone Loss It is unclear whether the increased efficiency of intestinal calcium absorption during pregnancy prevents a net loss of calcium from the mother.
|
From page 321... ...
Since the total amount of calcium transferred to the fetus is 30 g, which is equivalent to only 2.5% of maternal skeletal calcium, bone loss would be difficult to detect even with more precise techniques such as dual photon beam absorptiometry. Severe calcium and phosphorus restriction in rats increases maternal PTH synthesis, plasma 1,25-dihydroxycholecalciferol, and intestinal calcium absorption and reduces urinary calcium excretion.
|
From page 322... ...
The subcommittee recommends, therefore, that younger women with low calcium intakes should either increase their intake of food sources of calcium, such as milk or cheese, or, less preferably, add a supplement that provides 600 mg of calcium per day. In the United States, however, there have been no reports on the effect of maternal calcium supplementation on bone mineralization of the mother or the fetus.
|
From page 323... ...
, although the possible inhibitory effects of a meal high in phytate or fiber on calcium absorption have not been adequately investigated. It is unlikely that pregnant women over age 35 would benefit from calcium supplementation to a greater extent than younger women would.
|
From page 324... ...
Thus, the extent to which maternal vitamin D status regulates the placental transport of calcium is not clear, although the vitamin is necessary for the maintenance of maternal calcium status. Requirements The dietary requirement for vitamin D is highly dependent on exposure of the skin to ultraviolet light.
|
From page 325... ...
There are numerous examples of low 25hydroxycholecalciferol levels resulting from clothing that restricts exposure to ultraviolet light, e.g., in Bedouin (Biale et al., 1979) and Saudi Arabian (Serenius et al., 1984)
|
From page 326... ...
of vitamin D per day increased maternal and newborn 25-hydroxycholecalciferol levels in both spring and fall (Verity et al., 1981~. In Finland, supplementation given because of low 25-hydroxycholecalciferol levels quickly improved plasma levels of the vitamin (Kuoppala et al., 1986~.
|
From page 327... ...
The relative efficacy of maternal supplementation with vitamin D is greatest during the third trimester (Clements and Fraser, 1988~. Supplements of vitamin D2(ergocalciferol)
|
From page 328... ...
per day given to women in their third trimester was less effective than two very large doses of 15 mg (600,000 IU) given in the seventh and eighth months, based on increased serum calcium, reduced alkaline phosphatase, and increased birth weight (Marya et al., 1981~.
|
From page 329... ...
Vitamin D supplementation has no effect on maternal or umbilical cord blood magnesium concentrations (Cockburn et al., 1980; Verity et al., 1981~. Magnesium is probably actively transported to the fetus (Reitz et al., 1977~.
|
From page 330... ...
Nevertheless, there is some concern that low calcium intakes during pregnancy might impair bone mineral deposition, especially in women under age 25.
|
From page 331... ...
· Older pregnant women do not need higher calcium intakes than do those who are younger. Evidence does not support the practice of prescribing calcium for leg cramps during pregnancy.
|
From page 332... ...
1988. The relationship between calcium intake and pregnaney-indueed hypertension: up-to-date evidence.
|
From page 333... ...
1986. Cholecalciferol and placental calcium transport.
|
From page 334... ...
1988. Evidence for a novel parathyroid ho~mone-related protein in fetal lamb parathyroid glands and sheep placenta: comparisons with a similar protein implicated in humoral hypercalcaemia of malignancy.
|
From page 335... ...
1972. The influence of numerous pregnancies and lactations on bone dimensions in South African Bantu and Caucasian mothers.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.