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zoom RSS 小児のビタミンD不足

<<   作成日時 : 2008/06/06 00:08   >>

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 ボストン小児病院の研究によると、乳幼児の12%がビタミンD欠乏状態にあり、40%が低下している。不足していた子供の3分の1が手首と膝のエックス線骨密度で変化がみられた。少数には、くる病の所見があった。
 2004年の研究で、思春期の小児の42%がビタミンD不足であったので、どの年代も不足におちいっていると推測される。ビタミンDは骨成長と腸でのカルシウム吸収に必須であり、免疫系の調節もしている。
 太陽の紫外線が皮膚でビタミンDを生成するが、有害な紫外線から子どもを守りたい親が衣類や日焼け止めでカバーし、ダイエットでビタミンも不足する。ほとんどの食物はビタミンDを含んでいない。ビタミンD補充していない母乳で育った乳児が最もリスクが高い。
 「母乳は完全栄養食」と言われているが、ビタミンDは不足している。米国小児科学会は、生後2ヶ月から成人するまで、最低200国際単位のビタミンDを補充するように推奨している。ほとんどのミルクは推奨値にあるが、母乳には不足しているため、母乳栄養の乳児は補充する必要がある。
 全ての小児にビタミンDを補充すべきかどうかについては議論がある。
 幼児にジュースの代わりにビタミンD強化ミルクを与え、1日最低30分、体の一部に日光をあてる。という提案をしている人たちもいる。
 ビタミンD不足の母乳栄養の乳児に対する補充については、ほぼ合意が得られてきているが、その他については更なる研究が必要とされている。
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Kids' Low Vitamin D Worries Doctors
Researchers Urge Supplements for All Children; Diet Experts Disagree
By ALLYSON T. COLLINS
ABC News Medical Unit June 3, 2008
http://abcnews.go.com/Health/Diet/story?id=4982913&page=1

The sunshine vitamin is in the spotlight again -- and this time the focus is on infants and toddlers.

vitamins
In a new study, researchers suggest many children are not getting enough vitamin D.
(Getty/ABC News)

Many young children do not get enough vitamin D, one team of researchers said. And while experts agree on the problem, the solution is another matter.

In a study at Children's Hospital Boston, researchers found that 12 percent of infants and toddlers were deficient in vitamin D and 40 percent had below-optimal levels.

The findings, published in the June 2008 issue of Archives of Pediatrics & Adolescent Medicine, also showed that one-third of children who were deficient had changes in bone density seen on X-rays of the wrist and knee. A few even had signs of rickets, or softening of the bones caused by severe deficiency of vitamin D.

"We didn't pick up a lot of rickets, but we did pick up a lot of vitamin D deficiency," said Dr. Catherine Gordon, director of the Bone Health Program at Children's Hospital Boston and one of the study's co-authors. "We need to be concerned."

In 2004, Gordon and her colleagues found that 42 percent of adolescents were vitamin D deficient. This led them to wonder whether the problem began during childhood.

"I think these data suggest that vitamin D deficiency is common throughout the age spectrum now," Gordon said about the latest results.

Vitamin D is crucial for bone growth and calcium absorption in the intestine. It also plays a role in regulating the immune system.

The sun is the best source of vitamin D; ultraviolet rays trigger its production in the skin. Parents routinely cover young children with sunscreen, blankets or additional layers of clothing to protect them from harmful UV rays, so children may not have enough sun exposure to produce sufficient levels of vitamin D.

Diet is another source of the vitamin. Few foods naturally contain vitamin D, but milk products, bread and cereals are often fortified with it.

As expected, infants fed with enriched formulas and toddlers who routinely drank milk were more protected from vitamin D deficiency, and breast-fed infants who did not receive vitamin D supplements were at a higher risk.

"Breast milk is the perfect food," Gordon said. "It's the healthiest way to feed an infant, but it has been shown to be deficient in vitamin D."

The American Academy of Pediatrics recommends that infants and children receive a minimum of 200 international units of vitamin D daily, starting during the first two months of life and continuing through childhood and adolescence.

Most formulas provide the daily recommended value, but breast milk does not. To compensate, breast-fed infants can be given a liquid multivitamin drop that contains vitamin D.
Related
Vitamin D Could Cut Cancer Risk

Vitamin D and Supplements for All?

In light of these findings, Gordon said that routine supplementation of infants and children is a safe and cost-effective measure for correcting vitamin D deficiency.

Some doctors agree.

"There is every reason to supplement with vitamin D and no reason not to," said Dr. Robert Lustig, professor of clinical pediatrics at the University of California at San Francisco.

Lustig points out that the cost of supplementation presents a challenge, though. Vitamins are not considered medicines, and are generally not covered under health insurance policies.

Other experts worry about the potential harm that could result if children consume excess vitamin D. Like vitamins A and E, vitamin D is fat-soluble, so it is stored in the body's fat cells instead of eliminated in the urine. According to the National Institutes of Health, too much vitamin D can cause nausea, vomiting, constipation and weakness.

"Meeting the need is great, but exceeding the need is not always good," said Madelyn Fernstrom, professor and director of the UPMC Weight Management Center in Pittsburgh. "Especially with infants and toddlers, I think we should proceed with caution."

Keith Ayoob, associate professor of pediatrics at Albert Einstein College of Medicine in New York, agrees that routine supplementation is unnecessary at this point.

"The first line of defense is to find out why kids are not getting enough vitamin D and correct that," he said.

Ayoob and Fernstrom suggest that this deficiency is primarily a lifestyle problem, resulting from the fact that children are not consuming enough vitamin D to meet the guidelines.

"It doesn't matter how great a recommendation is if a parent is not using it," Fernstrom said.

In the study, low vitamin D levels were linked to lack of milk intake for many of the children. Therefore, Ayoob said dietary deficiencies should be addressed first.

"If you supplement them, they're still going to have a bad diet," he said. "They're going to have a very well-supplemented bad diet."

Fernstrom suggests a few simple changes that might remedy the problem: Giving toddlers vitamin-D fortified milk instead of juice and making sure at least a small part of the body, such as the hands or legs, are exposed to sunlight for about 30 minutes a day.

Experts do agree that one group should be routinely supplemented: infants who are breast-fed, as breast milk just doesn't have enough vitamin D.

The next step? Dr. James Taylor, professor in the department of pediatrics at the University of Washington, said a long-term study is needed to determine the lasting effects of vitamin D deficiency on infants and toddlers. Researchers should also look at whether supplements have positive effects on bone density.

"There's a lot of research on vitamin D right now," Taylor said. "I think we're not to the final answer yet. This study is just a piece of the puzzle."

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Many infants and toddlers don't get enough vitamin D
Researchers call for supplements for breastfeeding infants and increased milk intake for toddlers
June 2, 2008
http://www.childrenshospital.org/newsroom/Site1339/mainpageS1339P1sublevel433.html
Many otherwise healthy infants and toddlers have inadequate vitamin D levels that may put future bone health at risk, finds a study from Children's Hospital Boston. The major risk factor for infants was exclusive breastfeeding without vitamin D supplementation; for toddlers, it was inadequate milk consumption. Findings appear in the June issue of Archives of Pediatrics & Adolescent Medicine.

画像Led by Catherine Gordon, MD, MSc, Director of the Bone Health Program at Children's, the researchers studied 365 infants and toddlers who visited the hospital's general pediatric clinic for well-child exams at age 9 and 18 months, respectively. Blood testing found that 40 percent of the children had vitamin D levels below the optimum considered good for bone health, and 12 percent were frankly deficient.

Of the deficient group, 13 children (32.5 percent) had evidence of bone loss, as assessed by computed radiography of the wrist and knee. Three children (7.5 percent) had bone changes consistent with rickets (a softening of the bones that can lead to fractures, stunted growth and deformities like curved spine and bowed legs), although only one of these children had signs of rickets on physical examination.
Image
Catherine Gordon, MD, MSc
"We were struck by the number of children in our study with suboptimal vitamin D levels," says Gordon. "Vitamin D status is not routinely checked as part of routine care, and the majority of the children did not show signs of rickets or other evidence of a deficiency, so it is concerning that this problem would have otherwise gone undetected."

In infants, the major predictor of deficiency was exclusive breastfeeding without vitamin D supplements. Infants in this category were 10 times more likely to be vitamin D deficient than infants who were exclusively bottle-fed. (Breast milk does not contain vitamin D, whereas formula and cow's milk are fortified with the vitamin.) In toddlers, the major risk factor was inadequate milk consumption: blood vitamin D levels increased in close correlation with the number of cups per day of milk the child drank.

"As a pediatrician, I am pleased that breastfeeding has become more common among new mothers," says Gordon. "Of concern, however, is the rise in cases of rickets accompanying this trend. Our data suggest the importance of vitamin D supplementation for young children, and particularly breast-fed infants."
The authors were struck by the strength of the correlation between vitamin D deficiency and breastfeeding without supplementation, since only 8 percent of children in the study were exclusively breastfed. Although the American Academy of Pediatrics and Institute of Medicine recommend that infants and children receive 200 IU daily of supplemental vitamin D, few breastfed infants in this study were receiving such supplementation.

Since both dark skin and sunscreen reduce absorption of the ultraviolet rays that help the body manufacture vitamin D, the researchers expected to find skin pigmentation, sunscreen use and time spent outdoors to be predictive of vitamin D deficiency. However, their data revealed no significant correlation with these factors. They speculate that the layers of clothing babies are typically dressed in may prevent them from absorbing enough sunlight.

"We were surprised that neither skin pigmentation nor season significantly predicted vitamin D deficiency," Gordon says. "Our data suggest that unique risk factors for this problem can arise, ones that pediatric health care providers should be cognizant of in the care of young children."
The infant and toddler years are the first crucial period for laying down bone. Once bone mass reaches its peak--by age 18--it can never increase. No one really knows what will happen when children with bone loss enter adulthood and old age, but Gordon fears they may be predisposed to osteoporosis.

The study was funded by the Allen Foundation, Inc., the McCarthy Family Foundation, the National Institutes of Health, and the Maternal and Child Health Bureau of the U.S. Health Resources and Services Administration.

Contact:
Jamie Newton
617-919-3110
james.newton@childrens.harvard.edu

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