技术文章

New guidelines for vitamin D call for increasing the recommended dietary allowance （RDA） of vitamin D to 600 international units （IU） for everyone aged 1-70, and raising it to 800 IU for adults older than 70 to optimize bone health.

The guidelines, released by the Institute of Medicine （IOM）, also raised daily calcium RDAs.

The new guidelines call for a recommended dietary allowance of 700 milligrams of calcium per day for children aged 1 through 3, 1,000 milligrams daily for almost all children aged 4 through 8, 1,300 milligrams of calcium per day for adolescents aged 9 through 18, and 1,000 milligrams for all adults aged 19 through 50 and men until age 71. Women starting at age 51 and men and women aged 71 and older need 1,200 milligrams of calcium per day.

The majority of Americans and Canadians are getting sufficient vitamin D and calcium, the new guidelines state. Some adolescent girls aged 9-18 may fall below the daily recommended level of calcium intake, and some elderly people may have an inadequate intake of calcium and vitamin D.

The older vitamin D guidelines call for a recommended dietary allowance of 200 IU a day for people up to age 50, 400 IU a day for those ages 51 to 70, and 600 IU a day for those older than age 70.

Vitamin D helps the intestines better absorb calcium and plays an important role in bone health. It is often called the "sunshine vitamin" because our bodies make it when exposed to sunlight. It is often added to milk.

Growing numbers of studies link vitamin D deficiency to diseases such as heart disease, certain cancers, and diabetes. The studies show associations that indicate further investigation is needed and do not necessarily prove that vitamin D deficiency has a causative role. Many scientists were hoping that the new dietary intake levels would go even higher to reflect the findings of these studies.

But “we don’t think more is better,” says committee member Clifford J. Rosen, MD, a senior scientist at the Maine Medical Center Research Institute in Scarborough. “We believe that taking in amounts larger than 600 to 800 IU a day has no extra benefit for bones.”

“More isn’t necessarily better, and anything over the new upper intake levels may increase risks,” says Committee chair Catharine Ross, PhD, professor and Dorothy Foehr Huck Chair of the department of nutritional sciences at Pennsylvania State University in University Park.

The new upper intake levels for calcium are:

1,000 milligrams per day for infants up to 6 months
1,500 milligrams per day for infants 6 to 12 months
2,500 milligrams per day from ages 1 through 8
3,000 milligrams daily from ages 9 through 18
2,500 milligrams daily from ages 19 through 50
2,000 milligrams per day for all other age groups
Recommendations Promote Bone Health
The new vitamin D guidelines only refer to bone health, she says. Ross ls WebMD that that there is no conclusive evidence that vitamin D intake is related to cancer, heart disease, or immune function.

“There isn’t a strong suggestive body of evidence for those indicators,” she says.

Michal L. Melamed, MD, an assistant professor of medicine and epidemiology and population health at Albert Einstein College of Medicine in New York, reviewed the guidelines prior to their release. She says, “They went high enough given the evidence that is out there.”

“The IOM was cautious, and it is probably the right thing to do because we don’t have large randomized clinical trials that show higher levels of vitamin D are associated with improved health,” she says. “Those studies are ongoing.”

The new recommendations will provide a level of vitamin D that keeps people out of the deficiency range, she says.

Second Opinion
Michael F. Holick, MD, PhD, a professor of medicine, physiology, and biophysics at Boston University School of Medicine and the author of The Vitamin D Solution, says the new guidelines on vitamin D are “a step in the right direction.”

He hopes that as more information on the benefits of vitamin D comes out “the next committee will be even more convinced of the non-skeletal benefits of vitamin D.”

Robert P. Heaney, MD, a professor of medicine at Creighton University in Omaha, Neb., says of the new guidelines: “They are way too conservative. There is evidence to support higher numbers.”