Vitamin D is essential to building and maintaining strong bones, health experts say. Yet so many Americans — women, in particular — aren’t getting enough of it that in a report to the secretaries of the departments of Agriculture, and Health and Human Services’ Dietary Guidelines Advisory Committee called vitamin D a “shortfall nutrient … of public health concern.”
“Vitamin D is required for calcium absorption, and calcium is one of the major minerals in the bone,” said Erin Gaffney-Stomberg, a research physiologist and principal investigator at the U.S. Army Combat Capabilities Development Command Soldier Center’s Combat Feeding Directorate, Natick, Massachusetts.
“So if you don’t have adequate vitamin D status, your calcium absorption will be impaired,” Gaffney-Stomberg said.
In adults, severe vitamin D deficiency may lead to fragile, soft and misshapen bones, a condition called osteomalacia. Osteoporosis is a disease in which the density and quality of bones are reduced over time.
More than 80% of the 10 million Americans who have osteoporosis are women, according to the Department of Health and Human Services’ Office on Women’s Health.
Women are more affected because they typically have smaller, thinner and less-dense bones than men, said Joanne Porwoll, a nurse practitioner in endocrinology at Fort Belvoir Community Hospital in Virginia.
Other risk factors for osteoporosis include smoking and drinking more than three alcoholic beverages daily.
Lifestyle changes can lower the risk for osteoporosis, Porwoll said.
Those changes include doing weight-bearing activities and ensuring there’s enough vitamin D in the diet.
Porwoll said people with the highest risk of having a vitamin D deficiency include those who live or work in environments with minimal sun exposure, have darker skin pigmentation, have health disorders that affect gut absorption of nutrients, or who take medications that affect the metabolism of vitamin D.
“Vitamin D really is unique because it can actually be made in our bodies,” Gaffney-Stomberg said.
In response to sunlight, a form of cholesterol in the skin is transformed into vitamin D, she said. But exposing unprotected skin to the sun has health risks, the American Cancer Society warns.
People also can get vitamin D through foods, including fatty fishes such as salmon and mackerel and dairy products and cereals that have been fortified with vitamin D. However, studies have found that people generally have a very poor intake of vitamin D from food sources.
Gaffney-Stomberg cited a study of Soldiers in initial Army training that found 70 percent of the women consumed less than a third of recommended levels of vitamin D. For men, the figure was 55 percent. These statistics are similar to those found in the civilian population, she said.
Decreased bone mass at any age can lead to an increased risk of fracture. That’s what led Gaffney-Stomberg and other U.S. Army Research Institute of Environmental Medicine researchers to collaborate with the Combat Feeding Directorate to develop a food item called the Performance Readiness Bar. The PRB is a supplemental snack bar fortified with vitamin D and calcium to support bone health. The aim is for Army recruits to consume the bar to prevent stress fractures.
“Stress fractures are one of the most common injuries during initial Army training,” Gaffney-Stomberg said. “Trainees are 18 times more likely to sustain a stress fracture compared to active-duty service members, and women have a four times greater risk than men.”
The PRB is a result of research that showed Army recruits who consumed two bars containing calcium and vitamin D every day during basic training experienced greater increases in bone density compared to those who ate placebo bars, Gaffney-Stomberg said.
A four-year study of 4,000 recruits is underway by scientists at USARIEM to understand the risk factors associated with stress fractures in recruits and the extent to which the PRB makes a difference.
Porwoll suggests Military Health System beneficiaries talk with their primary care providers about whether they should take vitamin D supplements. She noted that some calcium supplements also contain vitamin D, and too much vitamin D can be harmful. The National Institutes of Health’s Office of Dietary Supplements provides recommended dietary allowances.
While vitamin D previously had been thought to lower the risk of some types of cancer, a large clinical trial by the NIH’s National Cancer Institute recently concluded there was no link. When it comes to good bone health, however, there’s no dispute about the benefit of vitamin D.