Vitamin D deficiency is associated with an increased risk of hip fracture

Underlying vitamin D deficiency in post-menopausal women is associated with increased risk of hip fracture, according to investigators at Brigham and Women's Hospital in Boston, Massachusetts. In a group of women with osteoporosis hospitalized for hip fracture, 50 percent were found to have a previously undetected vitamin D deficiency. In the control group, women who had not suffered a hip fracture but who were hospitalized for an elective hip replacement, only a very small percentage had vitamin D deficiency, although one-fourth of those women also had osteoporosis.

These findings were reported in the April 28, 1999, issue of the Journal of the American Medical Association. The study, conducted by Meryl S. LeBoff, MD; Lynn Kohlmeier, MD; Shelley Hurwitz, PhD; Jennifer Franklin, BA; John Wright, MD; and Julie Glowacki, PhD; of the Endocrine Hypertension Division, Department of Internal Medicine, and Department of Orthopedic Surgery, Brigham and Women's Hospital, Boston, was supported by grants from the National Institute on Aging (NIA) and the National Center for Research Resources (NCRR), components of the National Institutes of Health.

These investigators studied women admitted to either Brigham and Women's Hospital or the New England Baptist Hospital, both in Boston, between January 1995 and June 1998. A group of 98 postmenopausal women who normally reside in their own homes were chosen for the study. Women with bone deterioration from other causes were excluded from the study. There were 30 women with hip fractures caused by osteoporosis and 68 hospitalized for elective joint replacement. Of these 68, 17 women also had osteoporosis as determined by the World Health Organization bone density criteria.

All the participants answered questions regarding their lifestyle, reproductive history, calcium in their diet, and physical activity. Bone mineral density of the spine, hip, and total body were measured by dual X-ray absorptiometry (DXA) technique, as was body composition. Blood chemistry and urinary calcium levels were analyzed.

The two groups of women with osteoporosis did not differ significantly in either time since menopause or bone density in the spine or hip. They did, however, differ in total bone density. The women admitted for a hip fracture had fewer hours of exercise than the control group.

Fifty percent of the women with hip fractures were deficient in vitamin D, 36.7 percent had elevated parathyroid hormone (PTH) levels (a hormone which can stimulate loss of calcium from bone), and 81.8 percent had calcium in their urine, suggesting inappropriate calcium loss. Blood levels of calcium were lower in the women with hip fractures than in either elective group.

These researchers propose that vitamin D supplementation at the time of fracture may speed up recovery and reduce risk of fracture in the future. Current Dietary Reference Intake Guidelines contain a daily recommendation of 400 IU of vitamin D for people aged 51 through 70 and 600 IU for those over age 70.

"We know that a calcium-rich diet and regular weight-bearing exercise can help prevent osteoporosis. This new research suggests that an adequate intake of vitamin D, which the body uses to help absorb calcium, may help women to reduce their risk of hip fracture, even when osteoporosis is present," observed Dr. Evan C. Hadley, NIA Associate Director for geriatrics research. "Osteoporosis leads to more than 300,000 hip fractures each year, causing pain, frequent disability, and costly hospitalizations or long-term care. Prevention of such fractures would greatly improve the quality of life for many older women and men, as well as significantly reduce medical costs."

The bones in the body often undergo rebuilding. Some cells, osteoclasts, dissolve older parts of the bones. Then, bone-building cells known as osteoblasts create new bone using calcium and phosphorus. As people age, if osteoporosis develops, more bone is dissolved than is rebuilt, and the bones weaken and become prone to fracture. Also in many older persons, levels of vitamin D in the blood are low because they eat less or spend less time in the sun, which stimulates the body's own production of vitamin D.

Experts do not understand fully the causes of osteoporosis. However, they do know that lack of estrogen which accompanies menopause, diets low in calcium, and lack of exercise contribute to the problem. Eighty percent of older Americans who face the possibility of pain and debilitation from an osteoporosis-related fracture are women. One out of every two women and one in eight men over the age of 50 will have such a fracture sometime in the future. These fractures usually occur in the hip, wrist, and spine.