一天应该摄入多少维生素D

It's the vitamin that is associated with the sun, that helps strengthen our bones, and may do a lot more.  The U.S. Institute of Medicine has increased the recommended levels of vitamin D that it says people need to stay healthy.  But the panel's statement is not the last word on this vitamin. 

Many people take vitamin D supplements because vitamin D works with calcium to form strong bones. The latest recommendations say most  people under the age of 70 need 600 units a day.  Those 71 and older need 800 units daily. Previous recommendations were between 200 to 600 units daily.

Still, some doctors wonder if the new amounts recommended are enough.  "It's a big jump forward, but they still didn't go far enough," said Dr. Michael Holick at the Boston University School of Medicine.

Doctors like him say vitamin D has many other benefits. "There is a lot of evidence suggesting that increasing your vitamin D intake will reduce your risk of many serious chronic diseases," said Dr. Holick. 

Diseases like cancer, high blood pressure and heart disease.  A new study shows that exercise and vitamin D supplements can also prevent the elderly from falling. In addition, studies show that pregnant women can reduce their chances of having complications if they take 4,000 units of vitamin D each day.

But Dr. Michael Irwig, at George Washington University Medical School, says more work needs to be done to support these findings.  "The truth is, we really do not know definitively, just due to a lack of randomized trials," he said. 

Dr. Irwig tells some of his patients to take between 1,000 to 2,000 units of vitamin D daily because data from the Centers for Disease Control show that a lot of people do not get enough vitamin D -- even though the Institute of Medicine says most people can get enough through their food or from the sun.

The problem is, people absorb or make vitamin D differently.  The elderly cannot make it as effectively as younger people can. And those who are obese may have problems absorbing vitamin D.  Measuring the amount of vitamin D in the body is also tricky.

"Measuring vitamin D is very challenging just due to the types of measurement that are out there and the different techniques that are used so you can't compare one measurement to another, and they are not very precise measurements," said Dr. Irwig.

A study currently underway may answer the question of whether vitamin D plays a role in protection against heart disease and cancer.