Sardines may not appeal to your toddler, but that may be just what the doctor ordered. Researchers have published two studies in this week's online version of the journal Pediatrics that raise some concerns about whether children receive adequate amounts of vitamin D.
Vitamin D is abundant in fatty fish like sardines, tuna and salmon, and it's also found in fortified cereals, milk and orange juice. And the old-fashioned teaspoon of cod liver oil has about 400 international units of the vitamin, which is the current dose recommendation for children from the American Academy of Pediatrics.
Federal officials are now reviewing their recommended daily allowance, which is currently set at 200 IUs a day. The review is in response to mounting evidence that American adults as well as children are not getting enough vitamin D. And that vitamin D deficiency could be linked to a host of health problems, including cardiovascular disease, diabetes and certain cancers.
In one recent study, researchers from Albert Einstein College of Medicine of Yeshiva University and Johns Hopkins School of Medicine looked at federal health statistics on children between the ages of 1 and 21. They determined that 9 percent of them were deficient in vitamin D. That's nearly 8 million children who had less than 15 nanograms per milliliter of blood.
They also found that 61 percent — or 50.8 million children — were what researchers term "insufficient." These children had less than 30 nanograms per milliliter, though using this number as a standard is controversial, as the medical community does not agree on what constitutes optimal levels of vitamin D.
In the study, Dr. Michal Melamed, from Albert Einstein College, describes her findings as extremely surprising and worrisome. "After we turn 30, we start losing bone, so, if many of our young children don't have enough vitamin D and are not reaching peak bone mass, then, in 60 years, there'll probably be a lot more osteoporosis" among adults, she says.
The second study focused on teenagers. Researcher and epidemiologist Jared Reis, with the National Heart, Lung and Blood Institute, says adolescents with the lowest levels of vitamin D appeared to have two times the risk of high blood pressure; hyperglycemia or high blood glucose levels; and four times the risk of metabolic syndrome, which is a collection of cardiovascular risk factors, when compared with adolescents who had the highest levels of vitamin D. Reis says this suggests vitamin D may play some role in the development of these conditions.
But these studies are preliminary, Reis says, and weren't designed to confirm whether low vitamin D actually causes these health problems. To answer that, he says scientifically controlled studies have to be done.
This January, researchers funded by the National Institutes of Health will begin recruiting 20,000 adults to take part in large clinical trials of vitamin D and omega 3 fatty acids. The findings of this study, expected in about five years from inception, should shed some light on the health benefits of vitamin D. But the study focuses on older adults, not children, adolescents or middle-aged adults. Future studies will have to include these population groups as well.
Dr. Joann Manson directs preventive medicine at Brigham and Women's Hospital and is one of the principal investigators for the upcoming clinical trials. She cautions against jumping on the vitamin D megadose bandwagon until this research yields some definitive answers.
And it should yield some answers, she says: "What's particularly exciting is that vitamin D may have a role in reducing some of the health disparities that are seen in race and ethnicity, because it is known that African-Americans tend to have high risk of vitamin D deficiency, and they also have a higher frequency of diabetes, hypertension, heart failure and many other chronic health problems."
Definitive vitamin D research, says Manson, could provide that causal link between the vitamin deficiency and health problems.
Darker skin pigment inhibits the body's ability to synthesize vitamin D from the UV rays of the sun. Today, most Americans use sunscreen to protect against skin cancer. This blocks the harmful rays of the sun, but it also blocks production of vitamin D. To compensate, researchers like Melamed say people can try eating foods rich in the vitamin. "Things like sardines, salmon and tuna have vitamin D in them naturally, and older people will remember taking cod liver oil, which is very rich in vitamin D," she says.
But if kids don't find those foods appealing, Melamed says, parents can offer their children breakfast cereals, milk and orange juice.
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MELISSA BLOCK, host:
A majority of U.S. children may have vitamin D levels that are too low, and worrisome health problems in adolescence might also be linked to low vitamin D. Those are the findings in this week's online version of the journal Pediatrics.
Here's NPR's Patty Neighmond.
PATTY NEIGHMOND: There's been some evidence that vitamin D not only helps build bones but also helps build the immune system and may even guard against heart disease. Most of that research has been about vitamin D levels in adults. Now some researchers are turning their attention to children. In one new study, researchers looked at federal health statistics on children between the ages of one and 21. They determined that nine percent of them were deficient in the vitamin. That's nearly eight million children. Another 60 percent of children, about 51 million, had levels of vitamin D that were lower than what some doctors consider optimal.
Dr. Michal Melamed is a kidney specialist with New York's Albert Einstein College of Medicine and she headed the study.
Dr. MICHAL MELAMED (Kidney Specialist, Albert Einstein College of Medicine): After we turn 30, we start losing bone. And so, if so many of our young children don't have enough vitamin D, you know, potentially were not actually reaching the peak bone mass that we should be reaching. And in 60 years, there will probably a lot more osteoporosis.
NEIGHMOND: But it's not just future bone health that may suffer when children grow up with too little vitamin D. A second study in the journal focused on teenagers. Researcher Jared Reis with the National Heart, Lung and Blood Institute.
Dr. JARED REIS (Researcher, National Heart, Lung, and Blood Institute): Adolescents with the lowest levels of vitamin D appear to have about two times the risk of high blood pressure, of having hyperglycemia or high blood glucose levels and about four times the risk of metabolic syndrome, as compared to adolescents who had the highest levels of vitamin D, suggesting that vitamin D may play some role in the development of these conditions.
NEIGHMOND: But Reis says these studies were preliminary and not designed to confirm whether low vitamin D actually causes these health problems. To answer that, he says, more studies have to be done. And in January, researchers begin recruiting 20,000 adults to take part in a large scientific trial of vitamin D, along with omega 3 fatty acids. Dr. Joann Manson directs preventive medicine at Brigham and Women's Hospital and is one of the study's principal investigators. She cautions against jumping on the megadose vitamin D bandwagon until research yields some definitive answers.
Dr. JOANN MANSON (Director of Preventive Medicine, Brigham and Women's Hospital): And what's particularly exciting is that vitamin D may have a role in reducing some of the health disparities that are seen by race and ethnicity, because it is known that African-Americans tend to have higher risk of vitamin D deficiency, and they also have a higher frequency of diabetes, hypertension, heart failure.
NEIGHMOND: Darker skin pigment inhibits the body's ability to synthesize vitamin D from the UV rays of the sun. Researchers say if it does turn out that vitamin D in fact has dramatic health benefits, then deficiencies can be solved fairly simply. For starters, Dr. Michal Melamed says parents can offer children foods high in vitamin D.
Dr. MELAMED: Things like sardines, and salmon and tuna have vitamin D in them naturally. And older people will remember taking cod liver oil, which is very rich in vitamin D.
NEIGHMOND: But if kids don't find those foods appealing, then says Melamed, parents can offer breakfast cereals, milk and orange juice, which are all fortified with vitamin D. Right now, federal guidelines suggest only 200 international units of vitamin D for everyone up to 50 years old, but the government's now reviewing that number. The American Academy of Pediatrics one year ago doubled its recommendation for children to 400 international units a day, a common dose now found in vitamins for children.
Patty Neighmond, NPR News. Transcript provided by NPR, Copyright NPR.