"There's been increased case reports and people describing it over the past five to 10 years; whether this is a true increase is unclear," said Dr. Steven Abrams, a pediatrician at the Baylor College of Medicine who has been on previous AAP vitamin D guideline committees.
Because the Centers for Disease Control and Prevention does not have exact numbers on rickets cases, recent concerns about its return are difficult to quantify.
The new pediatric guidelines recommend a daily dose of 400 international units of vitamin D per child per day -- doubling the group's old recommendations.
"The recommendation is going to be essentially a supplement for every child and adolescent in the United States," said Dr. Frank R. Greer, a pediatrician at the University of Wisconsin and one of the authors of the guidelines.
Greer notes that while children could get an adequate amount of the nutrient from drinking six glasses of milk a day or eating fatty fish such as salmon and mackerel, children are unlikely to do either of those.
But he also stresses that parents should not over-supplement their children.
"What we don't want is for parents to give their children more than 400 units a day," he said.
Obstacles to Adequate Vitamin D
One problem with maintaining adequate vitamin D levels in children, and even in adults, has been that other wellness guidelines have gotten in the way.
Sun exposure, while necessary for vitamin D, is discouraged because of the risks of skin cancer. And mothers are encouraged to breastfeed their infants -- but with more than half of American women potentially vitamin D deficient, and with breast milk not a good source of the vitamin in general, many babies will not get adequate amounts from their diets.
The use of infant formula avoids that problem, because it is fortified with an adequate amount of vitamin D.
"Breastfeeding babies are at particular risk because there's not much vitamin D in human milk," said Greer.
"The rickets that's been seen in the United States has been largely in minority populations who've been part of the WIC [Women, Infants, Children] program, where they've been emphasizing breastfeeding," said Greer, noting that 55 percent of all infants in the U.S. are involved in the program to provide food, health care and nutrition information for low-income women.
And while breast milk may not be a good source of vitamin D in any case, underprivileged, minority populations are more likely to be deficient in the vitamin.
"Any kids whose mothers are vitamin D deficient ... are at risk for getting full-blown rickets," said Greer. "[The presence of rickets] usually becomes obvious when the child begins to walk."
But the rickets problem may also persist in these populations, as paying for vitamins, particularly in an economic downturn, could present a problem.
"They need to remember to give their babies vitamin D," Abrams said, but he also noted that few states provide the supplements to parents.
As Greer points out, the cost of a month's supply is not expensive, at $7 or $8 for a month's supply, but Abrams said even that could pose a problem.
"$8 to $10 is a cost some people just are not going to spend."
But avoiding rickets may not be the only reason to get those supplements. Another motive for the revised guidelines, according to the AAP, is to build up the body's defenses.
"New evidence supports a potential role for vitamin D in maintaining innate immunity and preventing diseases such as diabetes and cancer," write the authors in their abstract.
But evidence for that is less clear.
"The evidence is not real solid, but sufficient to err on the side of safety," said Thomas M. Badger, chairman of the department of physiology at the University of Arkansas for Medical Sciences.
Badger noted that vitamin D deficiency in children has been understudied, and short of full-blown rickets, physicians do not know much about the condition.
"In children, short of having clinical rickets, we don't really know what constitutes vitamin D deficiency and how severe it is," said Abrams.
While he worries that some will misinterpret the committee's new guidelines as an attack on breast milk, Abrams said he hopes that will be avoided. He said that while breast milk is a good source of nourishment for infants, it was never designed to be a source of vitamin D.
"The message we always try to give is that giving vitamins to your babies is in no way saying that breastfeeding isn't adequate," Abrams said.