Vitamin D in the Infant: Requirements for Safety

Article Summary

Weston A. Price ( a dentist now deceased) emphasized the special importance of nutrition surrounding the events of marriage and childbirth. The isolated pre-modern groups that Price found to be immune to dental caries and degenerative diseases all prescribed special diets to women--and in some cases men--prior to marriage or conception, to expectant mothers during pregnancy, and to mothers with nursing infants. Price's studies led him to believe that nutrition during the prenatal, perinatal and postnatal periods was paramount to the formation of children possessing the physical excellence characteristic of the groups he studied.

While much attention is currently focused on research showing that the needs of adults for vitamin D are much greater than once thought, very little information on vitamin D is available to those planning a pregnancy. While official recommendations for both pregnant women and nursing infants are unlikely to protect either the mother or the infant even from overt deficiency, research suggests that infants, like adults, may benefit from intakes of vitamin D much greater than the official recommendations. Accurate information about the role of vitamin D in pregnancy and lactation is therefore critically needed if we are to provide the next generation with the health its members deserve.

Official Recommendations

Expectant mothers-to-be nourish inside them growing, living beings that begin developing their skeletons just eight weeks after conception--a process dependent on vitamin D, calcium and phosphorus supplied by the mothers' diets. Maternal intake of vitamin D is necessary for proper fetal growth and bone mineralization, and supplies a growing store of vitamin D to the fetus that he or she will depend on as a newborn.1 An adequate store of vitamin D will protect the newborn against tetany, convulsions and heart failure.2

Although the fetal skeleton begins developing early in gestation, it is late in the third trimester when the bulk of fetal skeletal development takes place. The skeleton of an infant born six weeks prematurely contains only half as much calcium as that of a newborn carried to term, which is why infants born prematurely require more calcium than breast milk alone can supply.3

This rapid skeletal development late in pregnancy also requires phosphorus and vitamin D; because of the increased demand of the fetus for vitamin D, the mother's own stores of vitamin D are depleted over the course of the third trimester.2 For this reason, the American Academy of Pediatrics stated officially in 1963 that "amounts of vitamin D greater than those needed by the normal adult are required for optimal nutrition during the last trimester of pregnancy," while also lamenting the lack of data about exactly how much more vitamin D is required.3 Likewise, Nicholas Bishop of the University of Sheffield's Academic Department of Child Health cited evidence in the 2005 edition of the authoritative textbook, Vitamin D, that vitamin D levels are depleted during the last trimester of pregnancy.2

Yet somehow all this knowledge was lost on the U.S. Institute of Medicine's Food and Nutrition Board in 1997 when it officially declared that the transfer of vitamin D from the mother to the fetus is so small that the mother's vitamin D status is not affected. Citing a 1978 study showing that the average vitamin D level of pregnant women consuming small amounts of vitamin D at high latitudes was 9.1 ng/mL (just under the level required to protect against overt deficiency) the Institute concluded that "there is no additional need to increase the vitamin D age-related AI during pregnancy above that required for non-pregnant women."4 This conclusion is strange, not only because many of the mothers in this study must have had vitamin D levels below the average, but because the average level itself was already deficient.

The Institute did not cite a 1980 study that had been conducted just two years later showing that of 115 Asian women living in London and of 50 of their newborn infants, 36 percent of the women and 32 percent of the infants had no detectable vitamin D in their blood at all.5 Several years after the Institute issued its policy statement, Nicholas Bishop's research team showed that over 60 percent of infants born to mostly white mothers in the spring and early summer in Sheffield had umbilical cord blood levels of vitamin D under 8 ng/mL.2

It is on rather dubious grounds, then, that the Institute of Medicine recommends a daily intake of 200 IU for pregnant women, which it supposes "may actually represent an overestimate of true biological need."4 Until the 1997 publication of that recommendation, the Committee on Nutrition of the American Academy of Pediatrics recommended a daily intake of 400 IU, which they considered "adequate to provide for added demands during the second half of pregnancy and during lactation."3 In 2003, however, the Academy's Committee on Nutrition issued a joint statement with the Academy's Section on Breastfeeding and with Dr. Lawrence Gartner and Dr. Frank Greer, in which they overturned the 40-year position of the Academy in favor of adopting the lower so-called "overestimate" of the Institute of Medicine.6 Nicholas Bishop, on the other hand, recommended 400 IU per day during pregnancy in the 2005 edition of Vitamin D.2

All of these recommendations are based on our understanding of vitamin D's action on the skeletal system. Yet we know from research on adults that when we consider the many other roles of vitamin D, we find substantial evidence that optimal nutrition requires much more vitamin D than that which is required simply to maintain skeletal health.7

The Important Question

The question is, are these increased requirements also true for the developing fetus? Researchers from Norway conducted a small and relatively crude study in 2000 suggesting that maternal use of cod liver oil during pregnancy was associated with a 70 percent reduced risk of the child being diagnosed with type 1 diabetes by the age of 15.8 Unfortunately, the researchers neither took the dose of cod liver oil into account nor had any way of differentiating the effect of vitamin D from the other constituents of cod liver oil. Nevertheless, the study does provide preliminary evidence suggesting that vitamin D may play a much larger role in fetal nutrition than simply providing for growth and skeletal development. Future research may show that the developing fetus, like the adult, needs more vitamin D than previously thought.

Evidence suggests that an adult's requirement for vitamin D is 10 to 20 times the daily dose recommended by the Institute of Medicine for pregnant women,7,9 and there is certainly no reason to believe that a woman's need for vitamin D declines when she becomes pregnant. As we will see in the next section, vitamin D nutrition is at least as important for the nursing infant as it is for the developing fetus, and extra vitamin D during pregnancy provides newborn infants with essential stores of the vitamin that they will use in their first weeks of life. But stored vitamin D is not enough for infants--these delicate new beings must also be nourished by high-quality, vitamin D-rich breast milk from well-fed mothers and exposed to adequate sunshine as they face a new world in which their quality of life will be powerfully shaped by the nutritional experience of their first and most important years.

Sources of Vitamin D for the Nursing Infant

Immediately after birth, the direct transfer of the mother's own nutrition across the placental wall to her baby is no longer an option. The use of stored vitamin D, exposure to the UV-B portion of sunshine when available, and breast milk are the newborn's three natural methods of obtaining vitamin D. Supplementing with cod liver oil, artificial supplements, or vitamin D-fortified formula can also provide additional sources of vitamin D.

At birth, the vitamin D levels in the mother's blood are correlated closely with those in the blood of the baby's umbilical cord.10,11 The mother must therefore maintain optimal levels of vitamin D during pregnancy in order for the newborn to begin life with optimal stores of vitamin D.

These stores, however, are used up quickly. In 1989, researchers followed 39 pregnant women from the beginning of their third trimester until 24 weeks after birth, measuring the vitamin D levels of both the mothers and their infants.12 At birth, the average maternal vitamin D level was 34 ng/mL and the vitamin D levels of the infants were closely correlated with those of their mothers. During the 24 weeks after birth, the infants were exclusively breast fed and did not receive vitamin D supplements. Over the course of the first eight weeks, infant vitamin D levels declined substantially, after which they remained constant for the duration of the study. This suggests that the stores of vitamin D that infants accumulate as fetuses are used up within the first eight weeks of life, after which their vitamin D levels reach equilibrium with what they continue to acquire from sunshine, breast milk or supplements.

Infants, like adults, can only obtain vitamin D from sunshine when there is adequate UV-B available, which varies according to season and latitude. Also like adults, they obtain vitamin D from the sun in amounts proportionate to the surface of skin they have exposed to it. At most latitudes, however, there will be times of the year during which infants will not be able to obtain vitamin D from sunlight. For this reason, the vitamin D levels of infants who were studied in Cincinnati, Ohio, reached optimal levels of 41-45 ng/mL in the summer, but sank to 21 ng/mL in the winter. Infants born during the winter had an average level of only 16 ng/mL one month after birth.13

The Institute of Medicine and the American Academy of Pediatrics consider human milk to be a poor source of vitamin D.4,6 The Institute of Medicine cites research showing that the vitamin D content of a mother's milk has no effect on the nursing infant's vitamin D status because it is overwhelmed by the effect of sunlight. A closer look at these studies, however, suggests that the vitamin D content of human milk varies widely with the mother's diet, and, as one would logically expect, that the relative contributions of sunlight and breast milk to the infant's vitamin D status vary according to the availability of sunlight and the vitamin D content of the mother's milk.

On one end of the spectrum, nearly all reported cases of

Diabetes Type 1

A group of researchers led by Elina Hypponen published a landmark study in The Lancet in 2001 suggesting that intakes of vitamin D over 2000 IU per day in infancy may be able to nearly eradicate type 1 diabetes.24 The study began in Finland in 1966 when over 10,000 infants were enrolled and researchers recorded whether they were supplemented with the then-official recommendation of 2000 IU per day of vitamin D for the first year of life, more than this amount, less than this amount, or were not supplemented at all. They then followed the study participants for over 30 years until 1997, recording which of the participants were diagnosed with type 1 diabetes by that time and which were not.

The benefit associated with vitamin D occurred at the lowest and highest levels of vitamin D intake and at all points measured in between. Children who developed rickets were 2.6 times as likely to develop type 1 diabetes compared to children who did not develop rickets. Compared to infants who did not receive a supplement of vitamin D at all, those who supplemented regularly, most but not all of whom supplemented with 2000 IU per day or more, had an 88 percent reduced risk of type 1 diabetes. Out of those who supplemented regularly, those who received the dose of 2000 IU per day had a further reduced risk of 78 percent compared to those who received a lower dose. Those who received a dose higher than 2000 IU per day had an 86 percent reduced risk compared to those who received a lower dose. Thus, vitamin D administered during infancy appears to exert a powerful protection against type 1 diabetes in amounts that extend from those just sufficient to prevent rickets to those exceeding 2000 IU.