JoAnn E. Manson, MD, chief of preventive medicine at Brigham and Women’s Hospital, Boston

• The numbers don’t back up the hype.
Over the past few years, studies have given hope that getting more D might be the key to preventing a range of health problems, from cancer to diabetes. But a committee I was a member of, convened by the Institute of Medicine (IOM), recently examined all the existing data and ruled that these links are inconclusive and insufficient.

• Fewer people are deficient than we thought.
The IOM panel concluded that having between 20 and 30 nanograms per milliliter (ng/mL) of D in the blood is safe and healthy. But people with levels nearly twice that have been told they’re deficient.

• Our bodies make—and store—plenty of D.
The IOM’s new guidelines now call for an intake of 600 IU per day; most of us already get that from food, multivitamins, and everyday sun exposure. And our bodies naturally store any excess D we make, for those times when we don’t get enough.

YES: Most of of us would benefit from more.
John J. Cannell, MD, executive director of the Vitamin D Council

• The new guidelines are too low.
Despite the IOM ruling, I believe there are enough studies to suggest that larger doses, closer to 4,000 or 5,000 IU a day, are what people need. We know that people who have blood levels below 40 ng/mL have abnormal bone development and increased instances of cancer, cardiovascular diseases, and other chronic conditions.

• You can’t get enough D from food alone.
An adult would have to drink 50 glasses of milk a day or eat two to three servings of fish per meal to get that 5,000 IU per day. Taking a daily supplement and getting 5 to 10 concentrated minutes of sunshine without sunscreen is an easier alternative; obese people or those with darker skin will need more.

• There’s no harm in taking extra D.
Even the IOM panel concluded you can take up to 10,000 IU a day without adverse effects.

Our advice:
Ask your doctor to check your D level. If you’re below the optimal level outlined by the new guidelines, discuss taking a supplement. Though it may not help, it can’t hurt to increase your intake of D-rich foods like milk, fish, and fortified cereal. Just don’t ditch the sunscreen: It’s not worth it to risk developing skin cancer in pursuit of more D.