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TOPIC: Pregnancy and Vitamin D

Pregnancy and Vitamin D 05 Jul 2008 12:31 #8873

  • Debra
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I wanted to pull this section out of this article regarding vitamin D and Pregnancy from Today's Dietitian.

Pregnancy
Along with the general population, pregnant women have been found to have a high incidence of vitamin D deficiency.7 Vitamin D status of the infant at birth is related to the vitamin D status of the mother, as the cord blood will contain 50% to 60% of the maternal circulating concentrations of vitamin D.20

A vitamin D deficiency in pregnant women can cause problems for the mother and the fetus. Maternal effects of vitamin D deficiency include decreased serum calcium concentrations and possible decreased weight gain in the third trimester.21 Fetal vitamin D deficiency can delay growth and bone ossification and cause enamel hypoplasia and problems with calcium regulation (ie, hypocalcemia and tetany), decrease bone mineral content and skeletal mineralization, and cause congenital rickets and craniotabes (softening of the skull).21,22


At issue is whether a vitamin D deficiency decreases maternal weight gain, fetal growth, and birth weight and whether the serum vitamin D level for pregnant women should be higher.

In a study of pregnant women in the Netherlands, 8% of light-skinned women and more than 50% of darker pigmented women were vitamin D deficient, with levels below 25 nmol/L (a level that causes osteomalacia in adults).22 Had the criteria for vitamin D deficiency been set higher, an even greater number of pregnant women would have been identified as vitamin D deficient—up to 100% of the women in the study.

A 2006 study found a correlation of maternal milk intake to infant birth weight in pregnant women living in Calgary, Canada (51º North latitude), independent of other risk factors. As milk intake increased, so did birth weight.23 For each microgram (40 IU) increase in vitamin D intake, birth weight increased by 11 grams. No differences in infant head circumference and length were found between women with higher and lower milk consumption. No serum vitamin D levels were taken.

A study of lactating women given either 2,000 or 4,000 IU per day for three months increased serum vitamin D from 69 to 90.25 nmol/L and 81.5 to 97.9 nmol/L, respectively.20 All these values were within the normal reference range. In addition, the infants of the lactating women had significantly better vitamin D status at the end of the study, since their breast milk was richer in vitamin D. It appears supplementation does improve vitamin D status in pregnant women and their infants, and a vitamin D supplement up to 4,000 IU per day is not harmful.20

New Recommended Daily Intakes?
With all this information, we still have this unanswered question: How much vitamin D does the body need to produce a serum level that protects against disease?


In 1997, the Dietary Reference Intake for vitamin D was published by the Institute of Medicine.24 The adequate intake recommended for infants, children, and adults aged 19 to 50 is 200 IU per day; for adults aged 50 to 70, it is 400 IU per day; and for adults aged 70 or older, it is 600 IU per day.24 The adequate intake recommended for pregnant women is 200 IU. At present, the upper limit recommended for vitamin D is 2,000 IU per day.

Many researchers now believe these recommendations are too low. While the recommended intakes may prevent bone disease, they are not high enough to promote cellular health and prevent other diseases.

In the study of hip fractures previously cited, the authors found that a vitamin D level of 100 nmol/L was optimal and could prevent up to 25% of fractures.8 Reaching that level took a minimum of 700 to 800 IU per day and more if the baseline was below 44 nmol/L.

In a study of healthy young men in Nebraska (41° North latitude), it took 500 IU of vitamin D per day to prevent a seasonal fall in vitamin D and 1,000 IU per day to raise serum vitamin D by 12.5 nmol/L.

Calcium absorption, a measure of vitamin D status, was not maximized until a serum level of vitamin D reached 75 to 80 nmol/L.25,26 To achieve a serum vitamin D level of 80 nmol/L could require a daily intake of up to 2,200 IU, depending on baseline vitamin D levels.26 Individuals exposed to adequate sunlight have serum vitamin D concentrations averaging 150 nmol/L.27

At this point, there is a consensus among researchers and policy makers that the recommended daily allowance for vitamin D does need to be reassessed. Until that happens, the best recommendation is to have the serum vitamin D level checked. Make sure the doctor checks 25(OH)D. Next, encourage clients to go in the sun at least three times per week with maximum skin exposure and use sunscreen after 15 to 20 minutes. If their skin is darker, they will need to be in the sun for a longer period of time.

If they live above 35° North latitude (Atlanta, San Francisco), supplement vitamin D in the wintertime in doses of up to 2,200 IU per day to prevent seasonal declines. Infants need either sun exposure or supplemental vitamin D in a lower dose.

The recommendation to increase serum vitamin D levels in individuals who are deficient is to take 50,000 IU once per week for eight weeks. If the level remains low, repeat the 50,000 IU once per week for another eight weeks. Once a value of 50 nmol/L or greater is achieved, a supplement of 1,000 to 2,000 IU per day will maintain vitamin D in the normal range.5

Toxicity is not seen even at serum vitamin D levels of 250 nmol/L, requiring a vitamin D intake of 10,000 IU per day.26 Individuals exposed to adequate sunlight have serum vitamin D concentrations averaging 150 nmol/L, and lifeguards have closer to 250 nmol/L.27 Hathcock’s risk assessment estimates that 10,000 IU is safe ± five times the 2,000 IU currently recommended by the Food and Nutrition Board.13

In the era of food fortification, we have become complacent and have not recognized that factors such as sunscreen can affect vitamin D levels. The official recommendations sometimes lag behind the research, and dietitians should become more aware of potential risk for inadequacies of vitamin D in their patients, particularly in northern areas and among groups identified here as most at risk. In any case, it seems prudent, absent specific testing to establish adequacy, to recommend a daily supplement of at least 1,000 IU of vitamin D. For vitamin D content of foods click here .

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