補充維他命D和鈣的新建議

New Vitamin D and Calcium Recommendations: Experts Weigh In

What experts say about the Institute of Medicine's new recommendations for vitamin D and calcium.

By Kathleen M. Zelman, MPH, RD, LD
WebMD Feature

Reviewed by Laura J. Martin, MD

The Institute of Medicine has set new dietary intake levels for vitamin D and calcium for their role in bone health -- but says more research is needed to confirm other possible health benefits associated with these nutrients.

Over the last 10 years, there has been increasing interest in the health benefits of vitamin D. It’s been called the miracle vitamin, as numerous studies suggest the importance of vitamin D goes beyond bone health and may reduce the risk for cancer, heart disease, stroke, diabetes, autoimmune diseases, and more.

“Everyone wants vitamin D to be the new magic bullet to prevent all kinds of chronic disease, but the evidence is inconsistent and inconclusive at this time to warrant levels beyond our recommendations,” says Harvard’s JoAnn Manson, PhD, MD, and member of the IOM vitamin D and calcium committee.

The committee based its recommendations on a rigorous and thorough review of nearly 1,000 published studies. They were charged to evaluate current data and consider chronic disease implications and outcomes for disease prevention.

New Recommendations for Vitamin D, Calcium

The IOM set the following recommendations for vitamin D:

• Ages 1-70: 600 international units (IUs) per day. Older than 71: 800 IUs. The IOM previously said 200 IUs was adequate for people aged 50 and younger, 400 IU for people aged 51-70, and 600 IUs for people older than 70. 
• The tolerable upper limit (UL) is 4000 IUs for ages 9 and above (up from 2000 IU in the IOM's previous guidance).

The IOM's calcium recommendations, based on age, range from 700 to 1300 milligrams (mg) daily with a tolerable upper limit range of 1000-3000 mg.

Experts Respond to Vitamin D Safe Upper Limit

University of Cincinnati bone health expert Nelson Watts, MD applauds the establishing of 4000 IUs as the safe upper limit.

Robert Heaney, MD, a vitamin D researcher and Creighton University professor, agrees but would like to see it even higher. 

“I am delighted the upper limit for vitamin D has been doubled to 4000 IUs per day, although this is a conservative level, considering the body of scientific evidence indicating it should be 10,000 IUs," Heaney says. "However, few people need more than 4000 IUs, which will meet the needs of most healthy people, give physicians confidence to recommend supplementation, and allow research at higher vitamin D levels."

In his book, The Vitamin D Solution, Michael Holick, PhD, MD, author and vitamin D researcher, recommends an upper limit of 10,000 IUs for adults and 5,000 IUs for children.

Keep in mind that the upper limit is not the goal for taking supplements or evaluating food labels but is set to establish the safe upper limit.

Vitamin D Deficiency Overestimated?

Many adults and children were thought to have inadequate levels of vitamin D. But Manson says the problem may be confusion about the definition of adequacy and deficiency.

“It is our opinion that vitamin D deficiency is not as widespread as reported because laboratories across the country are using different cut points that overestimate the number of people with vitamin D deficiency,” Manson says.

The only way to know if you are getting enough vitamin D is to have your blood level checked.

All of the experts interviewed for this story were disappointed the committee did not assess the merit of the huge body of vitamin D evidence beyond bone health.

Sunlight and Supplements

The best food sources naturally rich in vitamin D are cod or fish liver oils, salmon, tuna, sardines, mackerel, and shrimp. Vitamin D is also found in egg yolks, beef liver, and mushrooms. Fortified foods -- such as milk, some yogurts, cereals, and orange juices -- also provide vitamin D.

Another option to increase vitamin D levels is to take dietary supplements to fill in the nutritional gaps; however, experts say to be careful.

“Manufacturers are putting more vitamin D in multivitamins and there are some single 5000 IUs vitamin D supplements that exceed the safe upper limit,” Watts says.

“Buy from reputable companies and don’t exceed the safe upper limit unless you are under a physician's care,” Holick says. He recommends children take 1000 IU and teenagers and adults 2000-3000 IUs supplements daily.

The body makes vitamin D when exposed to sunlight. But the IOM committee didn't factor that into the recommendations, because many factors (including, skin color, and geographic location) affect that process. Nor did the committee make any recommendations regarding supplements.

 “Individuals need to discuss supplementation with their health care provider,” Manson says.

 

相關鏈接:

Most getting enough calcium, vitamin D, report says - USATODAY.com

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