By getting enough vitamin D while pregnant, women may strengthen their children’s bones.

Scientists in the U.K. found that 9-year-old kids had higher bone mineral content, as reflected by bone mineral density (BMD) testing, if their mothers had gotten vitamin D supplements while pregnant.

Those kids may grow up with less risk of bone fractures from osteoporosis (thinning bones), note the researchers, who included Cyrus Cooper, FMedSci.

Osteoporosis can usually be diagnosed by measuring bone mineral density, which reflects the bone calcium content, a marker of bone mass or content.

Cooper is a professor at the MRC Epidemiology Resource Center at England’s University of Southampton.

The study appears in The Lancet.

Vitamin D’s Role

Calcium often gets the spotlight for its role in bone health. But vitamin D and other nutrients are also important.

Vitamin D is needed for the body to absorb calcium. It’s found in foods including egg yolks, liver, saltwater fish, and vitamin-D fortified products (such as milk and some breakfast cereals).

The researchers note that vitamin D deficiency can be commonly seen in healthy pregnant women and the elderly.

Supplements and sunshine are two more sources. Sunlight helps the body make vitamin D. Supplements containing vitamin D may also include other nutrients, such as calcium.

About 10-15 minutes of sunshine twice weekly -- without sunscreen -- is usually enough for the body to make vitamin D, according to the NIH’s Office of Dietary Supplements.

Falling Short on Vitamin D

Many people don’t get enough vitamin D. Diet and sun exposure are part of the issue, along with age and skin color.

Making vitamin D is harder for people older than 50 and those without light-colored skin. Melanin in darker skin makes it more difficult to make vitamin D from sunlight.

Seasons and geography also matter. Short winter days mean less opportunity to make vitamin D, especially in northern areas.

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Vitamin D Study

Cooper’s study included 160 white women who had babies in the early 1990s.

Blood tests showed that nearly half of the women didn’t have enough vitamin D, which was measured in late pregnancy. The shortfall was slight for 49 women (31 percent) and bigger for 28 others (18 percent), who had vitamin D deficiency.

None of the women was assigned to get more vitamin D from diet, supplements, or sun exposure.

Nine years later, the children the women had been carrying when the study started were evaluated with BMD tests.

The study showed lower bone mineral content for kids whose mothers hadn’t gotten vitamin D supplementation during pregnancy.

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Supplements for Moms?

The researchers are certain that many pregnant women got too little vitamin D.

If those women had taken vitamin D supplements, their kids might have built stronger bones that would be less likely to fracture later in life, the researchers write.

They call for a study to test that theory directly. A long-term study on the development of osteoporosis or fractures in the children may give us more insight into the role of vitamin D.

Of course, getting enough vitamin D wouldn’t just help the kids’ bones. The moms’ bones might also benefit.

Visit WebMD's Pregnancy Center

By Miranda Hitti, reviewed by Louise Chang, MD

SOURCES: Javaid, M. The Lancet, Jan. 7, 2006; vol 367: pp 36-43 Office of Dietary Supplements, “Dietary Supplement Fact Sheet: Vitamin D.” News release, The Lancet.