Calcium is vital for bone health and normal physiologic function. Hence, its consumption in the diet is important, as is an adequate level of vitamin D, which aids in calcium absorption. To address the issue of what constitutes adequate dietary calcium and vitamin D intake, the Institute of Medicine (IOM) issued guidelines in 2010 (1) that recommended a daily intake of calcium for most adults of 1000 to 1200 mg per day and vitamin D of 600 to 800 IUs per day. A variety of foods are good sources of dietary calcium. These include dairy products, sardines and dark leafy green vegetables like spinach, kale, turnips, and collard greens. Vitamin D is, strictly speaking, not an essential nutrient since it can be made from sunlight in the skin. However, there remains a significant fraction of the population with inadequate circulating levels of 25 (OH) vitamin D (the major circulating metabolite). Because calcium intake from food in many diets is below the IOM recommendations, many health care providers have advised their patients to take calcium and/or vitamin D supplements to maintain bone health. However, recent data have argued that there are side effects of daily calcium supplement intake with or without vitamin D and have also questioned the utility of their intake for preventing fragility fractures.
Therefore, there exists great concern among health care professionals as to what forms and doses of calcium and/or vitamin D are appropriate. This topic has been the subject of several of my previous blogs but recent published data and a position paper by the United States Preventive Services Task Force (USPSTF) suggests a need for me to write about it again.
The USPSTF is an independent panel of non-Federal experts in prevention and evidence-based medicine. Its recent report on vitamin D and calcium supplements to prevent fractures (2) stated the following: 1) The current evidence is insufficient to assess the balance of the benefits and harms of combined vitamin D and calcium supplementation for the primary prevention of fractures in premenopausal women or in men, 2) The current evidence is insufficient to assess the balance of the benefits and harms of daily supplementation with greater than 400 IU of vitamin D3 and greater than 1,000 mg of calcium for the primary prevention of fractures in noninstitutionalized postmenopausal women and 3) The USPSTF recommends against daily supplementation with 400 IU or less of vitamin D3 and 1,000 mg or less of calcium for the primary prevention of fractures in noninstitutionalized postmenopausal women.
These recommendations were based on a review of the available literature. The USPSTF was particularly influenced by the results of the Women’s Health Initiative clinical trial (3). This study examined 36,282 postmenopausal women, 50 to 79 years of age. Participants were randomly assigned to receive 1000 mg of calcium as calcium carbonate with 400 IU of vitamin D3 daily or placebo. Fractures were ascertained for an average follow-up period of 7 years. It found that in healthy postmenopausal women, calcium with vitamin D supplementation resulted in a small (6%, p<0.01) improvement in hip BMD, did not significantly affect fracture incidence, and increased the risk of kidney stones by 17% (CI, 1.02 to 1.34).
There also continues to be a concern that calcium supplements with or without vitamin D can increase cardiovascular events (4). In 2012 Bolland et al (5) published a subgroup analysis of women in the WHI study who did not self-prescribe calcium supplements at baseline and found an increased risk of cardiovascular events associated with the use of calcium (1000 mg) and vitamin D (400 IU). However, Prentice et al (6) also reviewed the WHI clinical trial data for women not taking calcium supplements at baseline and included data from the WHI observational study of 93,676 post-menopausal women in their assessment of the benefits of calcium and vitamin D. These authors concluded, “Long-term use of calcium and vitamin D appears to confer a reduction that may be substantial in the risk of hip fracture among postmenopausal women”. They also failed to identify a correlation between calcium intake and cardiovascular events. Hence, for the doses of calcium and vitamin D used in the WHI the conclusions of multiple studies are conflicting. However, there is stronger evidence for a significant risk associated with higher doses of calcium supplements than those used in the WHI. A study by Michaelsson et al (7) recently found that doses of calcium greater than 1400 mg/day correlated with higher death rates from all causes and from cardiovascular disease excluding stroke.
So what should health care providers recommend to their patients? Both the ASBMR (8) and National Osteoporosis Foundation (9) have issued responses to the USPSTF. The ASBMR points out that: “The USPSTF’s recommendations differ from the 2010 Institute of Medicine’s (IOM) findings, primarily because the USPSTF recommendations are based only on fracture outcomes, while the IOM included an examination of the underlying biology of the impact of calcium and vitamin”. Both organizations suggest that the best source of calcium is food and supplements should be taken only to compensate for shortfalls in the IOM recommendations. They also suggest that vitamin D supplements may be needed to achieve the recommended intake. Finally, the ASBMR was concerned that the USPSTF’s recommendations do not apply to institutionalized elderly who are at high risk for osteoporosis or to patients with established osteoporosis.
For patients with established osteoporosis it is reasonable to periodically examine serum 25 OH vitamin D levels and to supplement patients in order to maintain levels above 61 nmol/liter (~24 ng/mL) since this value is associated with a significant decrease in fracture incidence (10). However, there are also concerns about over-supplementation with calcium and vitamin D as intake greater than the IOM recommendations may be detrimental (1).
Farmington, Ct, USA
How Much Calcium And Vitamin D?
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