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Nutritional rickets has long been considered a disease caused by vitamin D deficiency, but recent data indicate that inadequate dietary calcium intake is an important cause of rickets, particularly in tropical countries. Children with rickets due to calcium deficiency do not have very low 25(OH)D concentrations, and serum 1,25[(OH).sub.2]D values are markedly elevated. Studies of Nigerian children with rickets demonstrated they have high fractional calcium absorption. A high-phytate diet was demonstrated to increase calcium absorption compared with the fasting state, and enzymatic dephytinization did not significantly improve calcium absorption. When given vitamin D, children with rickets have a marked increase in 1,25[(OH).sub.2]D concentrations without any change in fractional calcium absorption. No positive relationship was found between fractional calcium absorption and serum 25(OH)D concentrations in children on low-calcium diets. More research is needed to understand the interaction between calcium and vitamin D and the role of vitamin D in calcium absorption. doi: 10.1111/j.1753-4887.2010.00338.x

Increasing calcium absorption and bone calcium accretion to levels above those achieved by human milk-fed, full-term infants is possible with infant formulas. However, no data support such a goal or suggest that it is beneficial to short- or long-term bone health. Small differences in the bioavailability of calcium between infant formulas are unlikely to have long-term consequences. Long-term studies of the effects of infant feeding type on ultimate bone mass are needed. For now, the vitamin-replete breast-fed infant's rate of calcium accretion during the first year of life should be the standard targeted for infant formulas. Key words: bone mineral content, calcium absorption, human milk, minerals

Calcium supplementation has been shown to increase bone mineralization in children and adolescents. However, catch-up mineralization later in puberty appears likely if intake is consistent with usual average intakes in the United States. Ultimately, individualized risk assessment will be developed based on genetic and lifestyle factors that can be used to guide optimal calcium intake during childhood. Key words: calcium absorption, dietary requirements, puberty, bone mass

For full-term infants in the first 6 months of life, exclusive breastfeeding remains the nutritional standard for calcium intake. However, unsupplemented human milk does not meet the nutritional requirements for growth of the very-low-birth-weight (< 1500 g) infant. Methods for human milk fortification have been evaluated, and recent studies have demonstrated the safety of these fortifiers. Key words: human milk, fortification, minerals, prematurity

Nutritional rickets, an ancient disease that was thought to have been cured in the early part of the 20th century, has made an unexpected comeback in recent years throughout the world. Although the frequency of its occurrence is poorly documented, increasing case reports of rickets are apparently related to low dietary intake of vitamin D and calcium and decreased sunshine exposure. Greater awareness of this problem is needed, as are further data regarding vitamin D status and incidence of rickets among infants and toddlers. Routine provision of supplemental vitamin D to all breastfed infants remains controversial, but may become more widely recommended. Key Words: rickets, vitamin D, calcium, sunshine

For full-term infants in the first 6 months of life, exclusive breastfeeding remains the nutritional standard for calcium intake. However, unsupplemented human milk does not meet the nutritional requirements for growth of the very-low-birthweight (<1500 g) infant. Methods for human milk fortification have been evaluated, and recent studies have demonstrated the safety of these fortifiers.