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Recommended Daily Vitamin D Intake Gets a Boost

Most people get enough calcium and the "sunshine vitamin," and an expert panel cautions against taking too much of the nutrients
vitamin d supplement



ISTOCKPHOTO/SIMPLYTHEYU

Vitamin D deficiency has become something of a health bugaboo in recent years, especially after a 2009 study that declared three quarters of U.S. adults and teenagers deficient. Low levels of the vitamin—which is manufactured by the body when sunlight hits the skin and can be found in some fatty fish and fortified food products—have been linked to disparate conditions, such as a sluggish immune system and psychosis.

But a new report from the Institutes of Medicine (IOM), released November 30, concludes that the evidence linking vitamin D and calcium deficiency to anything but poor bone health is inconclusive. It also determined that most people in the U.S. and Canada are getting ample amounts of the vitamin. Even so, the organization is raising the level of recommended daily intake.

The new assessment recommends a daily vitamin D dietary allowance of 600 milligrams for most healthy people 9 years and older (with an estimated average requirement of 400 International Units per day—and no more than 4,000 IU of vitamin D per day). People 71 years and older should take 800 mg of the vitamin per day, according to the report. (Children aged 4 to 8 years should not have more than 3,000 IU/day and those aged 1 to 3 years should not have more than 2,500 IU/day.)

The updated daily recommendations are not directly comparable to previous sets, which were established in 1997 and are based on "adequate intakes" rather than on the newer recommended dietary allowance and estimate average requirement. Catharine Ross, chair of the IOM's review committee and a professor of nutrition at Pennsylvania State University, noted in a Tuesday press briefing that the two values are "like comparing apples to pears." (The previous adequate intake recommendations were 200 IU per day for infants through age 50, 400 IU/day for ages 51 to 70, and 600 IU/day for those 71 and older.)

Adequate intake was more of "a guesstimate," Patsy Brannon, a professor of nutritional sciences at Cornell University and member of the IOM review committee, said at the briefing. Those who did not meet the previous adequate intake levels were at a higher risk for deficiency, but "you cannot assume that individuals are deficient if they do not meet the adequate intake," she explained.

That the IOM is "recognizing that their 1997 recommendations are too low" is substantial progress, says David Hanley, a professor in the departments of Medicine, Community Health Sciences and Oncology at the University of Calgary, who was not involved in the new report.

The report also offered new recommendations for daily calcium intake:

•    Ages 1 to 3: recommended dietary allowance 700 mg/day (no more than 2,500 mg/day)
•    Ages 4 to 8: recommended dietary allowance 1,000 mg/day (no more than 2,500 mg/day)
•    Ages 9 to 18: recommended dietary allowance 1,300 mg/day (no more than 3,000 mg/day)
•    Ages 19 to 50: recommended dietary allowance 1,000 mg/day (no more than 2,500 mg/day)
•    Ages 51 and over: recommended dietary allowance 1,200 mg/day for all except men ages 51-70 who need only 1,000 mg/day (no more than 2,000 mg/day)

Adolescent girls ages 9 to 18 were the only group found to be lacking in either nutrient, and the committee recommended they needed to consume more calcium.

Nutrient rich
Despite all of the recent proclamations about widespread vitamin D deficiency, the new analysis found that "the majority of Americans and Canadians are receiving adequate amounts of both calcium and vitamin D." Why the sudden switch to sufficiency? It is not because North Americans have suddenly upped their intake. The difference has to do with the lab tests and concentration criteria that are used—neither of which is standardized.

Vitamin D is measured via levels of 25-hydroxyvitamin D in the blood. Cutoff points of sufficiency and deficiency "have not been based on rigorous science," Hanley says. And the IOM's new assessment uses a lower concentration of 25-hydroxyvitamin D to mark deficiency. And over the past several years, there has been "a slow ramping up of what that threshold is," Glenville Jones said at the press briefing. Jones, a member of the review committee, heads the biochemistry department at Queens University in Ontario.

Most people in the research the IOM assessed had what the group considered sufficient levels of 25-hydroxyvitamin D (50 nanomoles per liter as measured in the U.S. and 20 nanograms per mole as measured in Canada) despite not meeting daily intake recommendations. This incongruity suggests that despite increased caution about sun exposure to avoid skin cancer, people are still getting a substantial amount of vitamin D from natural synthesis. To be safe, however, the committee made their intake suggestions based "on the assumption of minimum sun exposure," Ross said.

Hanley worked with researchers from Osteoporosis Canada who published recommendations this summer in the Canadian Medical Association Journal, and they recommended 400 to 1,000 IU per day for optimum bone health in those 50 and younger. But the two recommendations fall within a comfortable range of one another. "We're not talking about major differences here," Hanley says. "These recommendations would be an improvement on what we have now," he notes. "Where the argument might come in is: What's optimal for bone?" His group's recommendations are likely higher because they were focused on bone health—as well as a population that generally receives less sunlight in winter months.

Deficient evidence
Despite having assessed 1,000 studies and reports and "listened to testimony from scientists and stakeholders" the IOM committee found that most published health benefits (aside from bone strength) provided "mixed and inconclusive results and could not be considered reliable," according to the report, which was commissioned by the U.S. and Canadian governments.

Evidence that vitamin D plays a role in fending off some cancers or preventing cardiovascular disease has emerged "largely through association, identified through population studies and not through controlled trials," Hanley says. "So it's not high-level evidence." Nevertheless, he notes, "it's probably true that vitamin D is important in many body systems" Hanley points out that some studies have uncovered a link between very high levels of 25-hydroxyvitamin D and pancreatic cancers, whereas other studies have found very low levels of the vitamin associated with the cancer. "None of the findings in relationship to cancer—both benefit and harm—are consistent," he says.

It may well be a matter of research catching up to biology. To really home in on the ideal levels of vitamin D, Hanley recommends studies that follow people deficient in vitamin D who are randomly assigned to a supplement or placebo group. "What were missing were studies of cause and effect," Ross explained.

Too much of a good thing
The IOM conclusions at least may stop those who may be getting excessive vitamin D and calcium via supplements. Too much vitamin D hurts the heart and kidneys, and too much calcium can lead to kidney stones. Other side effects include increased risk of death from any cause as well as increased risk of fractures, falls and possibly some cancers, the authors of the report noted in a summary.

So one of the committee's changes was trying to figure out "how much is too much" of these crucial nutrients, Ross explained. Previous evidence has shown definitive increase in harm for those taking more than 10,000 IU of vitamin D a day, but "we took a cautious approach" in assigning new upper limits, Ross said.

Nevertheless, the upper limit of 4,000 IU/day of vitamin D should not be a goal, Jones noted. "We don't recognize any benefit from taking a dose" between the recommended daily allowance and the top levels considered safe, he said.

Ross noted that the new recommendations will "have a shelf life of many years" in terms of setting health recommendations—influencing everything from nutritional labeling to school lunch composition.

In the meantime, there is "an urgent need" to standardize blood tests, Ross said. Currently, one person might be declared vitamin D deficient or sufficient depending on which test they are given. And for now, some experts recommend scaling back on the amount of screening for vitamin D deficiency. Such tests "probably should not be part of routine care," Steven Clinton, a professor of hematology and oncology at the Ohio State University and review committee member, said at the briefing. In the next decade, as tests become more consistent and more studies are done, he said, doctors will likely be able to provide patients personalized recommendations for vitamin D and calcium intake based on their family history and genetic profile.

But many more tests and trials remain to be done, not only to zero in on optimum doses of the nutrients, but also to explore their role in the human body. "As a basic scientist, I am still very excited about this molecule, which regulates hundreds—maybe thousands—of genes in the body," Jones said.

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