A lack of vitamin D — thought to be a problem of a bygone era — is showing up in growing numbers of women, children and the elderly, increasing the risk of bone disease and possibly other health problems.

Exposing only the face, hands and forearms to sunlight for 10 to 30 minutes, just two or three days a week, can usually produce all the vitamin D we need. Yet today, many people’s lifestyles and locations do not allow them to produce enough, making dietary sources vital.

Many North Americans have low blood levels of vitamin D, which might be caused by one of many reasons. For example, the dark skin of African-Americans tends to form active vitamin D in response to sunlight more slowly than does skin with less pigment. A lack of vitamin D is also common among the elderly, especially those who are institutionalized. Other reasons include low consumption of milk, no intake of vitamin supplements, seasonal changes and urban location.

Vitamin D helps our bodies absorb calcium from food and also plays a vital role in the constant remodeling of our bones. Calcium can’t be used properly for bone formation when children lack vitamin D, leading to skeletal deformities in the condition called rickets. Inadequate vitamin D isn’t as obvious in adults, but bone weakening can be significant. In one study of women with osteoporosis, those who consumed the most vitamin D from food and supplements developed 37% fewer hip fractures than did women who consumed the least. Other studies show that raising inadequate vitamin D intake can increase bone density, but results are not completely consistent. Some studies also link adequate calcium and vitamin D intake with a lower risk of colon cancer.

Experts recommend different amounts of vitamin D for people of different ages. For adults 19 to 50, it’s 200 IU of vitamin D daily. From age 51 to 69, that increases to 400 IU, and from age 70 onward, it increases again to 600 IU.

The primary food sources of vitamin D are milk (including soy milk, if it’s fortified), fortified breakfast cereals, naturally high-fat fish (such as salmon and mackerel) and egg yolks.

While we aim for 200 to 600 IU, some researchers suggest that elderly people with low blood levels, people who are not exposed to sunlight, people with intestinal diseases that keep them from absorbing fat properly, and people on chronic steroid medications may need even higher amounts.

“Nutrition Notes” is provided as a public service by the American Institute for Cancer Research, 1759 R Street, NW, Washington, DC 20009