Vitamin D is a fat-soluble vitamin that exists in two forms, vitamin D3 or cholecalciferol which is the mammalian form and vitamin D2 or ergocalciferol which is the fungal form (1, 2). From a nutritional perspective both forms are metabolized similarly (3). At birth, human infants have a limited amount of vitamin D stores that primarily reflect transfer from the mother during pregnancy (1, 2). After birth, vitamin D can be obtained by the infant through mother’s milk (0.5-1.8 micrograms per liter), and through supplements (1). Vitamin D can also be made in the infant’s skin when exposed to ultraviolet beta solar radiation (4). However, at latitudes greater than 37 degrees north or south the beta radiation is too low to enable vitamin D production during the late fall to early spring months. In addition, melanin pigmentation of the skin absorbs beta radiation and thus it limits the ability to make vitamin D for those with darker skin (5). Parents are advised to limit their infant’s exposure to ultraviolet solar radiation by use of hats, swaddling in blankets and avoidance of direct exposure to sunlight (6-8). This means that even though vitamin D can be made in the skin in some regions and seasons, the limited exposure of infants to sunshine renders this source to be minimal. Therefore, the main sources of vitamin D for the infant include vitamin D obtained from the mother during pregnancy and after birth from diet and supplements.

The best biological indicator of body stores of vitamin D from all sources is blood serum concentration of 25-hydroxyvitamin D (25(OH)D) (1). Values of 25(OH)D below a concentration of 30 nanomoles per liter (nmol/L) of serum indicate high risk of vitamin D deficiency, whereas healthy concentrations for infants are believed to be at or above 50 nmol/L (1). Body stores can decline by 50% over less than a month in infants (9), and thus without a source of vitamin D, vitamin D deficiency can rapidly develop.

Vitamin D deficiency in infants (10-18) is evident throughout the world, covering a wide range of geographic regions and cultures. This is in part because not all health care practitioners recommend vitamin D supplementation even after considering exclusive breastfeeding and dark skin pigmentation (19-23). Furthermore, parent noncompliance to supplementation is a widespread concern (24-26), in some cases due to parental perception that their infant does not like the supplement (27-30). Immigration and refugee status is also a risk factor for low vitamin D status in infants (31-33), including countries with high beta radiation exposure (34).

Vitamin D is required to maintain blood calcium and bone health. The consequences of vitamin D deficiency in infancy classically manifest as soft malformed bones (rickets), seizures due to low blood calcium and difficulty breathing (35-40). At the time of diagnosis, infants with vitamin D deficiency rickets have very low serum 25(OH)D concentration, below 25 nmol/L (41, 42) and most have not received vitamin D supplementation (6, 43). Vitamin D deficiency is also thought to increase risk of other diseases including type 1 diabetes later in childhood (44-48).

The most widely accepted approach to building healthy vitamin D stores in infants is through vitamin D supplementation. Based on randomized controlled trials, 5 (49, 50) to 10 micrograms daily (49, 51-56) is enough to support a serum 25(OH)D concentration of 50 nmol/L in infants from birth to one year. Educational strategies aimed at parents are effective in increasing infant vitamin D status (57). High dose bolus supplementation to rapidly build stores in infants (58) is not yet recommended as a public health strategy.

Recommendations for vitamin D intakes in infancy are available from various organizations throughout the world and are typically 5 (2) to 10 micrograms daily (1, 6, 59-62). Some organizations suggest greater amounts (25 to 30 micrograms daily) as a supplement to exclusive breastfeeding (63). Supplements are usually recommended to begin within the first month of birth and continue until that amount can be attained from other foods (1, 6, 59). For some cultures and countries, the introduction of alternative milks, such as fortified cow’s milk or infant formula, and cereals may provide an additional source. Strategies to increase the amount of vitamin D in newborns using high dosage maternal supplementation show potential in preventing vitamin D deficiency in newborn infants (64-66), but are not part of public health policy recommendations at this time. If an infant is diagnosed with rickets, global consensus recommendations for the treatment of vitamin D deficiency have recently been published (41).

There appears to be consistency across the world that newborn infants are at an elevated risk of vitamin D deficiency and that a vitamin D supplement to exclusive breastfeeding is highly recommended in the primary prevention of vitamin D deficiency and rickets (1, 2, 6, 59-63). Public health actions including information dissemination to parents and health care providers need to be strengthened to reduce the incidence of vitamin D deficiency.

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