Supplement to breast-feeding may prevent rickets. (African American Infants at High Risk).
This semantic confusion may be obstructing efforts to prevent rickets, in the face of a small but alarming resurgence in a condition that until recently had been considered virtually extinct in the United States, Dr. Thomas Welch said at a pediatric meeting sponsored by the Children's Hospital Medical Center of Cincinnati.
"Some zealots make the outrageous claim that there is no rickets in breastfed infants," said Dr. Welch, who observed that, in actuality, breast-fed infants bear a higher risk.
After the early part of the 20th century, vitamin D supplementation, the enrichment of cow's milk, and an appreciation of the value of sun exposure virtually eradicated rickets in this country. "For years, it was hard to teach residents about it," said Dr. Welch, formerly the director of nephrology and hypertension at the medical center. He is now professor and chairman of the department of pediatrics at the State University of New York, Syracuse.
But now it's back. One recent article documented 30 cases in a single state, North Carolina, in the last decade--18 of them in 18 months. Dr. Welch said he sees two to three cases per year in his own practice. The group at particular risk appears to be breast-fed African American infants.
Rickets--insufficient mineralization of infant bone--may have systemic causes, but the majority of cases are nutritional in etiology: a deficiency of dietary calcium (extremely rare) or of the vitamin D needed to absorb and retain the mineral.
A precursor of vitamin D, 7-dehydrocholesterol, is naturally present in the human skin; it is transformed to calciferol by the action of ultraviolet light, and this compound is metabolized in the liver and kidney to active vitamin D (1, 25 dihydrocholecalciferol) itself.
The increased incidence of rickets accompanied a decrease in sun exposure that resulted from industrialization in the 19th century. Early solutions to the problem emphasized sunbathing--"till the skin turns red," in the words of one pediatrician in the 1920s--and supplementation with cod liver oil. For much of the last century, cow's milk has been enriched with vitamin D.
The reappearance of the disease may be an unintended consequence of otherwise praiseworthy efforts to increase breast-feeding. Several widely read books on the subject, including the La Leche League International's classic manual, "The Womanly Art of Breast Feeding," explicitly suggest that vitamin D supplementation is unnecessary in nursing infants of well-nourished mothers, Dr. Welch said.
In actuality breast milk contains too little of the compound, and maternal vitamin D supplementation would have to reach toxic levels to achieve an adequate milk concentration, he said.
Breast-feeding advocates who consider heretical the idea of supplementing "a perfect food" should realize that vitamin D is not in fact a vitamin. "It's not naturally present in any food and is more properly considered a steroid hormone," Dr. Welch said.
To prevent rickets, all infants and children should receive 400 IU of vitamin D daily. In breast-fed infants, this means supplementation. The alternative, sun exposure, is difficult to quantitate and inadvisable for other health reasons.
Supplementation is particularly critical for infants and children with dark skin because pigmentation interferes with the transmission of ultraviolet light and puts them at higher risk for rickets. The majority of recent cases have been in breast-fed African American children, Dr. Welch pointed out.
Clinical features of rickets include failure to thrive and short stature, frontal bossing, delayed closure of the anterior fontanelle, delayed dentition, bowing of weight-bearing bones, and hypotonia. Indrawing of the softened ribs along the attachment of the diaphragm causes a hollowing called Harrison's sulcus. Skull bones can be indented by finger pressure, and there can be expansion of the costochondral junctions. Seizures are a late feature.
In terms of diagnostic tests, serum calcium can be low or normal, serum phosphorus is low, and plasma alkaline phosphatase activity is much increased. Wrist joint x-rays show cupping and fraying of the metaphyses and a widened epiphyseal plate.
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|Date:||Mar 1, 2002|
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