Daily vitamin D helps prevent bone loss
Insufficiency can lead to osteoporosis, other poor health outcomes
By Mary I. O’Connor, MD, and Julie Glowacki, PhD
Vitamin D has been a hot topic in health care news recently, with numerous new studies extolling its benefits. Vitamin D is necessary for maintenance of normal blood levels of calcium and phosphorus, and works in conjunction with other vitamins, minerals and hormones to promote bone mineralization and to regulate bone resorption.
Natural vitamin D3, cholecalciferol, is obtained through exposure of skin to ultraviolet B photons and ingestion of certain foods (e.g. fatty fishes and fish liver oils), but many people need an additional dietary supplement to meet the recommended daily intake. One common synthetic form has the structure of ergocalciferol, vitamin D2. Both forms are converted by the liver to 25-hydroxyvitamin D (25(OH)D) and the kidneys to 1,25-hydroxyvitamin D (1,25(OH)D), which signals the intestines to increase calcium and phosphorus absorption.
Calcium and phosphorus—which are needed for building and maintaining strong bones and reducing bone fragility––are ineffective without the guidance of vitamin D.
A study from the U.S. Department of Agriculture’s Human Nutrition Research Center on Aging noted that 25(OH)D concentrations of 75-80 nmol/L are required for optimal bone health. This level of 25(OH)D decreased parathyroid hormone concentrations, which resulted in decreased rates of bone loss and reduced rates of fracture.1 Bones decrease in density as a natural part of the aging process and without intervention, can lead to osteoporosis.
Vitamin D may also reduce fracture rates via another mechanism. A double-blind, placebo-controlled study by the Elderly Day Hospital in London determined that vitamin D supplementation “improves neuromuscular or neuroprotective function…explain[ing] the mechanism whereby vitamin D reduces falls and fractures.” The study also showed that vitamin D affects functional performance, balance and reaction time.2
Additional studies have shown improved musculoskeletal function and increased coordination among people who take vitamin D supplements along with calcium and phosphorus. Research conducted at the University of Basel in Switzerland found that vitamin D may affect factors directly related to muscle strength. The study identified specific receptors for vitamin D in human muscle tissue and also noted that elderly persons with higher vitamin D serum levels have increased muscle strength and a lower number of falls.3
The 2004 Surgeon General’s Report on Bone Health and Osteoporosis highlights vitamin D intake as important for the absorption of calcium and bone mineralization and currently recommends a total daily intake of 200-600 International Units (IU) of vitamin D, with higher doses for the frail elderly.4 Recommendations for daily intake of vitamin D are expected to increase substantially in the near future to ensure that people achieve the required blood levels.
The AAOS currently recommends 400-600 IU of vitamin D daily for adults over 50, in accordance with the 2004 Surgeon General’s Report and the National Institutes of Health’s Office of Dietary Supplements (see table). Vitamin D intake should not exceed an upper limit of 1000 IU for infants and 2000 IU for children, adults and the elderly.
Although vitamin D3 was previously considered equipotent to vitamin D2, some data show that it leads to a 1.7-fold greater increment in circulating 25(OH)D levels than does vitamin D2.5 Many over-the-counter vitamin products do not indicate which form of vitamin D they contain.
Data indicate that 50 percent of women are not consuming the recommended amounts of vitamin D.6 These women are at risk for hypovitaminosis D, which can lead to osteomalacia and secondary hyperparathyroidism. Hypovitaminosis D can occur if a patient does not take the recommended levels of vitamin D, has little or limited exposure to sun, is lactose intolerant or a strict vegetarian, or if the patient’s kidneys are unable to convert vitamin D to its active hormone form.6 The current prevalence of osteomalacia in the United States is not known.
Vitamin D is vital to our aging population, especially women, for the prevention of bone loss. Osteoporosis is a long-term effect of vitamin D insufficiency, as vitamin D is essential in the absorption of calcium. Currently, more than 25 million Americans suffer from osteoporosis, 80 percent of whom are women. Millions more Americans have low bone mass, leaving them susceptible to developing this condition.
Osteoporotic fractures are a leading cause of disability, deformity, pain and even death in the elderly. More than 1.5 million fractures annually are associated with osteoporosis. Falls are second only to motor vehicle crashes as the most common mechanism of injury and account for 30 percent of all emergency trauma cases. In a recent analysis of community-dwelling postmenopausal women with hip fracture, 50 percent had deficient 25(OH)D levels and 37 percent had secondary hyperparathyroidism.7 Determination of the underlying cause of a fragility fracture requires a team approach and is essential for postoperative management and prevention of further fractures.
Osteoporosis places a considerable burden of disease on society. It is vital, therefore, that physicians promote proven preventive measures such as vitamin D intake in appropriate doses.
1. Dawson-Hughes, B: Racial/ethnic considerations in making recommendations for vitamin D for adult and elderly men and women. Am J Clin Nutr 2004;80:6:1763S-1766S.
2. Dhesi JK, Jackson SH, Bearne LM, et al: Vitamin D supplementation improves neuromuscular function in older people who fall. Age Aging 2004;33(6):589-595.
3. Bischoff, HA, Stahelin HB, Dick W, et al: Effects of vitamin D and calcium supplementation in falls: a randomized controlled trial. J Bone Miner Res 2003;18(2):343-351.
4. U.S. Department of Health and Human Services. Bone Health and Osteoporosis: A Report of the Surgeon General. Rockville, MD: U.S. Department of Health and Human Services, Office of the Surgeon General, 2004.
5. Trang HM, Cole DE, Rubin LA, Pierratos A, Siu S, Vieth R: Evidence that Vitamin D3 increases serum 25-hydroxyvitamin D more efficiently than does Vitamin D2. Am J Clin Nutr 1998;68(4):845-858.
6. National Institutes of Health Office of Dietary Supplements. Dietary Supplement Fact Sheet: Vitamin D. Web site: http://dietary-supplements.info.nih.gov/factsheets/vitamind.asp
7. LeBoff M, Kohlmeier L, Hurwitz S, Franklin J, Wright J, Glowacki J: Occult vitamin D deficiency in postmenopausal US women with acute hip fracture. JAMA 1999;281(16):1505-1511.
Mary I. O’Connor, MD, is chairman of the AAOS Women’s Health Issues Committee. Julie Glowacki, PhD, is director of skeletal biology in the department of orthopaedic surgery at Brigham and Women’s Hospital and Harvard Medical School, Boston.