The number of people in the United States and Canada with vitamin D deficiency may be overestimated because of inconsistent testing methods, according to a report(www.iom.edu) from the Institute of Medicine, or IOM. In fact, the new guidelines say that the majority of people in North America are meeting their needs for vitamin D and calcium.
Steven Clinton, M.D., a member of the IOM committee that reviewed dietary reference intakes for the two nutrients, said during a Nov. 30 news conference that there has been a large and unnecessary increase in the number of tests for vitamin D levels in recent years.
Clinton, a professor of internal medicine at the Ohio State University College of Medicine in Columbus, said vitamin D testing should not be part of routine medical care, and physicians should instead assess individual patients for risk factors.
The committee's report resulted from requests by the U.S. and Canadian governments for the IOM to assess available data on health outcomes related to calcium and vitamin D. The IOM asked the committee to review the evidence and issue updated recommendations for daily intake.
Committee chair A. Catharine Ross, Ph.D., professor and the Dorothy Foehr Huck Chair in the department of nutritional sciences at the College of Health and Human Development at Pennsylvania State University in University Park, said the panel's findings confirmed the benefits of calcium and vitamin D related to bone health. However, reviews of about two dozen other health outcomes -- including cancer, cardiovascular disease, hypertension and diabetes -- found insufficient and sometimes conflicting data regarding the nutrients' benefits.
"Although we believe that a role for calcium and vitamin D in other health outcomes should continue to be explored, we could not find solid evidence that consuming more of either nutrient would protect the public from chronic diseases ranging from cancer to diabetes to improved immune function," Ross said.
The IOM committee determined that the level of serum 25-hydroxyvitamin D (25[OH]D) that is needed for good bone health for most individuals was 50 nanomoles per liter, or 50 nmol/L, and according to the committee, national surveys in the United States and Canada indicate average blood levels are above that mark.
In its report, the committee said, "a considerable overestimation of the levels of vitamin D deficiency" exists in North America because of the current use of cut-points that exceed 50 nmol/L, including some higher than 125 nmol/L.
According to the committee, patients are at risk of deficiency at serum 25(OH)D levels less than 30 nmol/L, and some, but not all, are potentially at risk for inadequacy at serum 25(OH)D levels between 30 nmol/L and 50 nmol/L.
"The current lack of evidence-based consensus guidelines is problematic and of concern because individuals with serum 25(OH)D levels above 50 nmol/L may at times be classified as deficient and treated with high-dose supplements of vitamin D containing many times the levels of intake recommended by this report," committee members said.
The committee, which reviewed data from more than 1,000 studies and heard testimony from numerous scientists and other stakeholders, established the following intake categories for both vitamin D and calcium:
- estimated average requirement, or EAR, which reflects the average amount of the nutrients needed by normal, healthy people;
- recommended dietary allowance, or RDA, which identifies the level of intake likely to meet the needs of nearly 98 percent of the population; and
- tolerable upper intake level, or UL, which is defined as the point at which the potential harm from too much of a nutrient increases.
The committee determined that for most North Americans, regardless of age group, an EAR of 400 international units, or IUs, of vitamin D per day is needed. An RDA of 600 IUs was set for children ages 1 year and older, as well as for adolescents, pregnant and lactating women, and adults as old as 70.
For people ages 71 and older, an RDA of 800 IUs of vitamin D per day is advisable, the committee said. Other subgroups, such as those with dark skin pigmentation, also may be at increased risk for getting too little vitamin D.
ULs range from 1,000 IUs per day for infants to 4,000 IUs per day for people ages 9 years and older. Elevated levels of vitamin D are known to cause kidney and tissue damage, the committee said.
Ross said the committee assumed minimal sun exposure when establishing recommendations for vitamin D because exposure varies greatly from person to person.
- children ages 1 through 3 years should receive 700 mg of calcium per day;
- children ages 4 through 8 years should receive 1,000 mg per day;
- adolescents need 1,300 mg per day;
- women ages 19 through 50 and men as old as 70 need 1,000 mg daily; and
- women 51 and older and men 71 and older need 1,200 mg per day.
ULs for calcium ranged from 1,000 IUs in infants to 3,000 IUs in adolescents and teenagers.
Despite the committee's findings that the majority of people in North America receive adequate levels of calcium and vitamin D, Ross said supplementation still is appropriate from some groups, including calcium for girls ages 9-18 years and older women.
However, Patsy Brannon, Ph.D., professor in the Division of Nutritional Sciences at Cornell University in Ithaca, N.Y., cautioned that some older Americans are at risk for hypercalcemia because of the misuse of supplements.
Ross said the committee's recommendations are intended for prevention of disease in healthy people. People with chronic conditions should talk to their health care professionals about the levels of vitamin D and calcium they should be receiving, Brannon said. Some chronic conditions, such as kidney disease, affect metabolism of those nutrients.
Clinton called on medical organizations with physician education programs to ensure that clinicians know the appropriate calcium and vitamin D intake recommendations for different age groups.