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DRI Dietary Reference Intakes Calcium Vitamin D
emerged regarding vitamin D intake and hypercalcemia in infants. Stearns (1968) commented that Fomon et al. (1966) did not study the infants long enough, because the greatest differences in the Jeans and Stearns (1938) study appeared after 6 months. Also, a report from 1959 (Graham, 1959) suggested that a serum calcium level obtained from a study in Glasgow of infants with hypercalcemia ages 3 weeks to 11 months was associated with an estimated vitamin D intake of 1,320 IU/day. Overall, on balance, 1,800 IU/day is reasonable as a NOAEL and offers an appropriate starting point.
Infants 0 to 6 Months of Age
The first order of importance is to protect young infants, and the intake of 1,800 IU/day may not be entirely protective of such young infants. As the UL can reasonably be considered to affect all non-growth retarded infants at greater than 37 weeks gestational age at birth, and given the current practice to begin vitamin D supplementation within days of birth (Wagner and Greer, 2008), it is necessary to ensure an absence of toxicity in infants as small as 2,500 to 3,000 grams who would meet this definition. As such, applying an uncertainty factor of 0.5 and rounding would reasonably give a level of 1,000 IU/day, which is also about 400 IU/kg body weight per day, a dose that can reasonably be considered an upper safety level on a body weight basis. This UL is the same as the UL established in 1997 (IOM, 1997).
Infants 6 to 12 Months of Age
Consistent with general principles of toxicology, the committee considered that an infant’s capacity to handle excess substances such as vitamin D is likely increased with increased body size, organ maturation, and growth needs. Therefore, for older infants it is reasonable to consider a higher UL than for younger infants, although available data are inadequate for quantitative risk assessment. Also, the endpoint is acknowledged to be relatively insensitive. The UL for infants 6 to 12 months of age is increased by 500 IU/day from that established for infants 0 to 6 months of age, to a value of 1,500 IU/day. This reflects a more cautious approach than would be taken if the UL were doubled and is consistent with public health protection. This UL is slightly greater than the UL for vitamin D established for this life stage group in 1997, but is consistent with the toxicological principles that older infants are likely to have greater tolerances than younger infants (IOM, 1997).