I’m concerned that I may not be getting adequate vitamin D. How much is enough?

Q. I eat a pretty healthy diet and also take a multivitamin. Still, I’m concerned that I may not be getting adequate vitamin D. How much is enough?

A. Vitamin D is certainly important. For example, it helps us absorb calcium, which is key to maintaining healthy bones. Most Americans, though, don’t get enough. Up to 90% of people between the ages of 51 and 70 are considered deficient in the vitamin. Vitamin D is available in many foods, particularly fortified milk. Other rich sources are salmon, canned tuna, sardines, eggs, fortified cereal, beef liver, and Swiss cheese. It is also made in the body upon exposure to the sun’s ultraviolet rays—which is why it’s sometimes called the “sunshine vitamin.” As we age, however, it becomes more difficult for the body to make vitamin D from sunlight. Moreover, sunscreen—recommended as protection against skin cancer—all but blocks the body’s ability to make vitamin D. Ironically, preliminary research suggests that vitamin D protects against skin cancer as well as lymphomas and cancers of the lung, colon, and prostate. If you’re between the ages of 51 and 70, aim for at least 400 IU (international units) of vitamin D daily. Some studies recommend twice that amount (but not more than 2,000 IU). Also, get 10 to 15 minutes of sun 2 to 3 times a week.