This article summarizes the new 2011 report on dietary requirements for calcium and vitamin D from the Institute of Medicine (IOM). An IOM Committee charged with determining the population needs for these nutrients in North America conducted a comprehensive review of the evidence for both skeletal and extraskeletal outcomes. The Committee concluded that available scientific evidence supports a key role of calcium and vitamin D in skeletal health, consistent with a cause-and-effect relationship and providing a sound basis for determination of intake requirements. For extraskeletal outcomes, including cancer, cardiovascular disease, diabetes, and autoimmune disorders, the evidence was inconsistent, inconclusive as to causality, and insufficient to inform nutritional requirements. Randomized clinical trial evidence for extraskeletal outcomes was limited and generally uninformative. Based on bone health, Recommended Dietary Allowances (RDAs; covering requirements of ≥97.5% of the population) for calcium range from 700 to 1300 mg/d for life-stage groups at least 1 yr of age. For vitamin D, RDAs of 600 IU/d for ages 1–70 yr and 800 IU/d for ages 71 yr and older, corresponding to a serum 25-hydroxyvitamin D level of at least 20 ng/ml (50 nmol/liter), meet the requirements of at least 97.5% of the population. RDAs for vitamin D were derived based on conditions of minimal sun exposure due to wide variability in vitamin D synthesis from ultraviolet light and the risks of skin cancer. Higher values were not consistently associated with greater benefit, and for some outcomes U-shaped associations were observed, with risks at both low and high levels. The Committee concluded that the prevalence of vitamin D inadequacy in North America has been overestimated. Urgent research and clinical priorities were identified, including reassessment of laboratory ranges for 25-hydroxyvitamin D, to avoid problems of both undertreatment and overtreatment.

The IOM, at the request of agencies of the U.S. and Canadian governments, assembled a committee to update the DRIs for calcium and vitamin D based upon a rigorous and comprehensive review of the scientific data. The IOM Committee included 14 scientists with a broad range of expertise, assisted by experienced IOM staff members. The DRI process involves identification of health outcomes, or “indicators,” that are consistently and causally linked to the nutrient of interest, determination of the Estimated Average Requirement (EAR; corresponding to the median intake needs of the population), and calculation of the level of intake that would “cover” (meet) the requirements of at least 97.5% of the population [defined as the Recommended Dietary Allowance (RDA), corresponding to 2 sd above the median needs]. The DRI process also specifies the tolerable upper intake level (UL; the highest daily intake of the nutrient that is likely to pose no risk). When the evidence base is insufficient for development of the EAR/RDA, an adequate intake (AI) level may be estimated instead. Importantly, the DRIs are developed for “normal healthy persons” in the North American population (not intended for individuals with specific disease states) and are provided separately for several age and gender life-stage groups (Table 1​1).). Other charges for the Committee were to assess the dietary intakes of calcium and vitamin D in the U.S. and Canadian populations, as well as to identify research needs. The IOM Committee further specified that, due to the unique feature of cutaneous synthesis of vitamin D and the variation in synthesis due to seasonality of solar exposure, skin pigmentation, individual genetic factors, sunscreen use, latitude, outdoor activity, and other factors, as well as concerns about sun exposure and skin cancer, the DRIs for vitamin D would be based on an assumption of minimal or no sun exposure.

The IOM Committee concluded that the evidence that vitamin D or calcium reduced risk of nonskeletal chronic disease outcomes was inconsistent, inconclusive, and did not meet criteria for establishing cause-and-effect relationships. Randomized trial evidence was sparse, and few trials assessed these outcomes as primary prespecified endpoints. Moreover, emerging evidence suggested a curvilinear or U-shaped curve for several outcomes related to vitamin D, including cardiovascular disease, vascular calcification, falls, frailty, pancreatic cancer, and all-cause mortality (7,8,9,10,11), with the lowest risk at moderate levels and increased risk at both low and high levels of 25OHD. These studies are reviewed in detail in the report (1). Although future research may elucidate clear benefits and possibly even different requirement levels for vitamin D in relation to these nonskeletal outcomes, existing data cannot support such conclusions.

The indicators considered in the determination of ULs included hypercalcemia, hypercalciuria, vascular and soft tissue calcification, nephrolithiasis, and, for vitamin D, emerging evidence of a U-shaped relationship for all-cause mortality, cardiovascular disease, selected cancers, falls, and fractures. The 1997 ULs for calcium were 2500 mg/d for all ages above 1 yr, whereas the ULs for calcium now range from 1000–3000 mg/d, depending on life-stage group (Table 1​1).). For vitamin D, the ULs are now 4000 IU/d for ages 9 and older but are lower for infants and young children (Table 1​1).). The 1997 ULs for vitamin D were 2000 IU/d for most age groups. The starting point for the current UL for vitamin D was 10,000 IU/d, because lower intakes have not been linked to hypercalcemia or acute toxicity. However, given that toxicity is not the appropriate basis for a UL that is intended to reflect long-term chronic intake and to be used for public health purposes, this value was corrected for uncertainty based on chronic disease outcomes and all-cause mortality, as well as emerging concerns about risks at serum 25OHD levels above 50 ng/ml (125 nmol/liter). Thus, the Committee followed an approach to maximize public health protection. The UL is not intended as a target intake; rather, the risk for harm begins to increase once intakes surpass this level.

Guidelines regarding the use of serum markers of vitamin D status for medical management of individual patients and for screening were beyond the scope of the Committee’s charge, and evidence-based consensus guidelines are not available. However, these issues should be addressed by appropriate federal agencies and professional organizations in light of the findings in this report. As noted above, the Committee recognized that serum 25OHD is a useful integrated marker of vitamin D exposure, incorporating endogenous synthesis from solar exposure, dietary intake from foods, fortified products, and/or supplements, and other factors. However, the Committee also recognized that observational studies of correlations between 25OHD and clinical outcomes are subject to confounding and do not prove causation. Concerns about inaccurate or imprecise serum 25OHD measurements are being overcome by methodological advances, frequent quality assessments, and accurate calibration tools. In contrast, serum 1,25-dihydroxyvitamin D represents a more complex endocrine parameter, regulated by calcium and PTH status and affected by kidney function. After a careful review of available literature, the Committee concluded that serum 25OHD levels of 16 ng/ml (40 nmol/liter) cover the requirements of approximately half the population, and levels of 20 ng/ml (50 nmol/liter) cover the requirements of at least 97.5% of the population. These levels will be useful to clinicians as they consider management of patients under their care. For upper levels of serum 25OHD, sparse data are available, particularly regarding long-term effects of chronically high concentrations, and a margin of safety for public health recommendations is prudent. Thus, serum 25OHD levels above 50 ng/ml (125 nmol/liter) should raise concerns among clinicians about potential adverse effects.

Major food sources of calcium include dairy products, selected low-oxalate vegetables, legumes, nuts, and fortified foods; for vitamin D, primary sources are fortified dairy products, fortified foods, and fatty fish. Based on national government surveys in the United States and Canada, it appears that most groups have adequate intake of calcium (as defined by intakes above the EAR), with the exception of girls aged 9–18 who have high requirements. The data underscore the need to increase calcium intake among girls in mid-to-late childhood and adolescence; in contrast, among postmenopausal women, high calcium intake from supplements may be concerning. Regarding vitamin D, average intake from foods tends to be less than 400 IU/d, but mean 25OHD levels have been above 20 ng/ml (50 nmol/liter) in representative samples. Thus, based on these data and a level of 20 ng/ml (50 nmol/liter) identified as meeting the needs of at least 97.5% of the population across all life-stage groups, it appears that the majority of the North American population currently is meeting its needs for vitamin D. Nonetheless, subgroups of individuals, particularly those with poor nutrition, those living at northerly latitudes or in institutions, or those with dark skin pigmentation may be at increased risk of not meeting their needs, especially if their 25OHD levels are below 16 ng/ml (40 nmol/liter), the level identified as the average requirement as discussed above.

The Committee identified a large number of uncertainties surrounding the DRI values, as well as extensive research needs. A particular priority is rigorous, large-scale, randomized clinical trials to test the effects of vitamin D on skeletal and nonskeletal outcomes, as well as to identify threshold effects and possible adverse effects where present. Elucidating the biology of the diverse effects of vitamin D, as well as effects of sun exposure, adiposity, body composition, race/ethnicity, and genetic factors on these associations, is also of great importance.

The available scientific evidence supports a key role for calcium and vitamin D in skeletal health, providing a sound basis for DRIs. The evidence, however, is not yet compelling that either nutrient confers benefits for, or is causally related to, extraskeletal health outcomes. Moreover, existing evidence suggests that nearly all individuals meet their needs at intake levels (RDAs) provided in this report and, for vitamin D, at 25OHD levels of at least 20 ng/ml (50 nmol/liter) even under conditions of minimal sun exposure. Furthermore, higher levels have not been shown consistently to confer greater benefits, challenging the concept that “more is better.” The Committee finds that the prevalence of vitamin D inadequacy in the North American population has been overestimated by some groups due to the use of inappropriate cut-points that greatly exceed the levels identified in this report. Serum concentrations of 25OHD above 30 ng/ml (75 nmol/liter) are not consistently associated with increased benefit, and risks have been identified for some outcomes at 25OHD levels above 50 ng/ml (125 nmol/liter). Additional research, including large-scale, randomized clinical trials, is needed. In the meantime, however, we believe that there is an urgent clinical and public health need for consensus cut-points for serum 25OHD inadequacy to avoid problems of both undertreatment and overtreatment.