A large percentage of people aged 50 or older, particularly women, have osteoporosis. Canadian researchers found that 19 percent of women (and 3% of men) aged 50 years and older have osteoporosis.1 The National Osteoporosis Foundation reports that 10 million Americans have osteoporosis and 34 million have low bone mass.2
The prevalence of inadequate intake of calcium and vitamin D is relatively high. Based on 2004 dietary and supplement intake among 10,879 Canadian respondents aged 50 and older, 45% to 69% had inadequate intake of calcium, and 54% to 66% had inadequate intake of vitamin D.
The National Health and Nutrition Examination Survey3 indicates women in the U.S. consume an average of 833 milligrams of calcium daily as compared to the U.S. Recommended Daily Allowance (RDA) of 1,200 mg daily. Similarly, women aged 50 and older consume only 176 IU of vitamin D as compared to 600 IU of the U.S. RDA for vitamin D. Between low dietary intakes and menopause, women in the U.S. do not consume enough calcium to prevent gradual losses in bone calcium content.
When estrogen production decreases, calcium absorption decreases and bone resorption increases. Resorption means the process by which osteoclasts, or bone cells, break down bone and releases minerals, resulting in a transfer of calcium from bone fluid to the blood. Bone loss can lead to osteoporosis in which weakened bones may fracture.
The National Institute of Health randomly assigned 36,282 postmenopausal women in the Women's Health Initiative clinical trial to receive 1,000 mg of calcium carbonate with 400 IU of vitamin D3 daily or a placebo. Researchers measured their bone density, and ascertained fractures over an average 7-year period. Among healthy postmenopausal women, calcium with vitamin D supplementation resulted in a modest but significant improvement in hip bone density. Calcium and vitamin D supplementation reduced the risk of hip fracture by 29 percent among women with an adherence of 80 percent or more.4
A meta-analysis identified eight controlled trials to evaluate vitamin D3 supplementation with or without calcium. Vitamin D3 supplementation showed a 70% probability of being a better treatment than placebo for the prevention of non-vertebral fractures, hip fractures, and non-vertebral, non-hip fractures. Compared to calcium supplementation, vitamin D3 plus calcium reduced non-vertebral fractures and non-vertebral, non-hip fractures, but did not reduce hip fractures. This meta-analysis supports the use of vitamin D3 of 800 IU daily.5