Screening for Vitamin D Deficiency: A Systematic Review for the U.S. Preventive Services Task Force

Vitamin D is obtained through food consumption and synthesis in the skin after ultraviolet (UV) B exposure (1). Researchers have reported associations between low 25-hydroxyvitamin D [25-(OH)D] levels and risk for fractures (26), falls (7, 8), cardio... show more

Vitamin D is obtained through food consumption and synthesis in the skin after ultraviolet (UV) B exposure (1). Researchers have reported associations between low 25-hydroxyvitamin D [25-(OH)D] levels and risk for fractures (26), falls (7, 8), cardiovascular disease (914), colorectal cancer (1320), diabetes (13, 14, 2129), depressed mood (13, 14, 30, 31), cognitive decline (13, 14), and death (13, 32). Vitamin D deficiency is determined by measuring total serum 25-(OH)D concentrations (33). Measuring 25-(OH)D levels is complicated by the presence of multiple assays (34); evidence of intermethod and interlaboratory variability in measurement (3543); and the lack of an internationally recognized, commutable vitamin D reference standard (44). Efforts to increase standardization are in progress (34, 44). There is no consensus on optimal 25-(OH)D concentrations. Although experts generally agree that levels lower than 50 nmol/L (20 ng/mL) are associated with bone health (36, 45), disagreement exists about whether optimal 25-(OH)D levels are higher than this threshold (Table 1). According to NHANES (National Health and Nutrition Examination Survey) data from 2001 to 2006, 33% of the U.S. population was at risk for 25-(OH)D levels below 50 nmol/L (20 ng/mL) (47) and 77% had 25-(OH)D levels below 75 nmol/L (30 ng/mL) (48). Risk factors for low vitamin D levels include darker skin pigmentation (33), low vitamin D intake (4951), little or no UVB exposure (49, 50, 5254), and obesity (4951, 55). Older age (4953), female sex (49, 51, 52), low physical activity (49, 50, 53), low education attainment (48), and low health status (51, 54) were factors also associated with vitamin D deficiency in some studies. Table 1. Summary of Current Opinions About Appropriate 25-(OH)D Level Cutoffs for Defining Vitamin D Deficiency and Associations Between These Cutoffs and Health Outcomes* Vitamin D deficiency is treated by increasing dietary intake of food fortified with vitamin D or oral vitamin D treatment. Two commonly available vitamin D treatments (vitamin D3 [cholecalciferol] and vitamin D2 [ergocalciferol]) are available in several forms (for example, tablet and gel capsule), dosages (for example, 200 to 500000 IU), and dosing regimens (for example, daily, weekly, monthly, or yearly) and can be given in combination with oral calcium (56, 57). Potential harms of vitamin D treatment include hypercalcemia, hyperphosphatemia, suppressed parathyroid hormone levels, and hypercalciuria (46, 58, 59). Although very high levels of vitamin D are associated with other potential harms, these events are rare with typical replacement doses (Table 1). Screening for vitamin D deficiency can identify persons with low levels who might benefit from treatment. This report reviews the current evidence on vitamin D screening in asymptomatic adults to help the U.S. Preventive Services Task Force (USPSTF) develop a recommendation statement. Although the USPSTF has not previously issued recommendations on screening for vitamin D deficiency, it has made recommendations on vitamin D supplementation to prevent adverse health outcomes (for example, falls, fractures, cancer, and cardiovascular disease) in populations not necessarily vitamin Ddeficient (that is, general populations who may or may not have been deficient) (6063). Methods Scope of the Review We developed a review protocol and analytic framework (Appendix Figure 1) that included the following key questions: Appendix Figure 1. Analytic framework. Numbers on figures indicate key questions. For a list of key questions, see the Methods section or Table 2. 1. Is there direct evidence that screening for vitamin D deficiency results in improved health outcomes? 1a. Are there differences in screening efficacy between patient subgroups? 2. What are the harms of screening (for example, risk for procedure, false positives, or false negatives)? 3. Does treatment of vitamin D deficiency using vitamin D lead to improved health outcomes? 3a. Are there differences in efficacy between patient subgroups? 4. What are the adverse effects of treatment of vitamin D deficiency using vitamin D? 4a. Are there differences in adverse effects between patient subgroups? Detailed methods and data for this review are contained in the full report, including search strategies, inclusion criteria, abstraction and quality rating tables, and contextual questions (46). We developed our protocol using a standardized process after gathering input from experts and the public. The analytic framework focuses on direct evidence that screening for vitamin D deficiency improves important health outcomes (for example, death, falls, fractures, functional status, or risk for cancer) versus not screening. Further, the framework details evidence that treatment in persons found to have vitamin D deficiency is associated with improved health outcomes, harms resulting from screening or subsequent treatment, and how effects of screening and treatment vary in subgroups defined by demographic and other factors (for example, body mass index, UV exposure, and institutionalized status). We did not review the accuracy of vitamin D testing because of the lack of an accepted reference standard and studies reporting diagnostic accuracy. For the purposes of this report, the term vitamin Ddeficient refers to populations in which at least 90% of persons have 25-(OH)D levels of 75 nmol/L (30 ng/mL) or less. For studies that did not restrict enrollment to persons with 25-(OH)D levels of 75 nmol/L (30 ng/mL), we used the mean 25-(OH)D level plus the SD multiplied by 1.282 to approximate the 90th percentile to determine whether this level was at or below the 75-nmol/L (30-ng/mL) threshold. Because of uncertainty about what 25-(OH)D level constitutes deficiency, we stratified studies according to whether at least 90% of persons had levels less than 50 nmol/L (<20 ng/mL in this report) or at least 90% had levels less than 75 nmol/L (30 ng/mL) with show less