Draft Research Plan

Vitamin D Deficiency in Adults: Screening

October 25, 2018

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This figure is the analytic framework depicting the four key questions and the research approach that will guide the evidence review for this topic. In general, the figure illustrates the overarching and first key question of whether screening for vitamin D deficiency leads to reduced all-cause mortality; reduced incidence of fractures and falls; reduced incidence of cancer, cardiovascular disease, and diabetes; improved physical functioning; and improved quality of life. The framework starts on the left and follows the intervention pathway for the population of interest, namely asymptomatic adults without underlying disorders of bone metabolism and who are not known to be vitamin D deficient. Moving from left to right, the second key question examines whether any harms result from such screening. The third key question examines whether treating vitamin D deficiency leads to reduced all-cause mortality; reduced incidence of fractures and falls; reduced incidence of cancer, cardiovascular disease, and diabetes; improved physical functioning; and improved quality of life. The fourth key question evaluates whether any harms result from such treatment.

Abbreviation: KQ=Key Question.

1. a. Does screening for vitamin D deficiency result in improved health outcomes?
    b. Does screening efficacy vary among patient subpopulations at higher risk for vitamin D deficiency (e.g., persons residing in institutions, with obesity, with low levels of sun exposure, or who are older)?
2. What are the harms of screening for vitamin D deficiency?
3. a. Does treatment of vitamin D deficiency with vitamin D result in improved health outcomes?
    b. Does treatment efficacy vary among patient subpopulations at higher risk for vitamin D deficiency (e.g., persons residing in institutions, with obesity, with low levels of sun exposure, or who are older)?
4. a. What are the harms of treatment of vitamin D deficiency with vitamin D?
    b. Do harms vary among patient subpopulations at higher risk for vitamin D deficiency (e.g., persons residing in institutions, with obesity, with low levels of sun exposure, or who are older)? 

Contextual questions will not be systematically reviewed and are not shown in the Analytic Framework.

  1. What are the various assays for measuring serum vitamin D (including total and free 25-hydroxyvitamin D and 1,25-dihydroxycholecalciferol), and what is known about the intermethod and interlaboratory variability of these assays?
  2. In observational studies, what is the association between vitamin D use or serum vitamin D levels and selected health outcomes (i.e., mortality, fractures, falls, cardiovascular disease, and cancer)?
  3. What is the relationship between vitamin D use and selected intermediate outcomes (i.e., bone mineral density, blood pressure, and measures of physical or muscle strength)?

The Proposed Research Approach identifies the study characteristics and criteria that the Evidence-based Practice Center will use to search for publications and to determine whether identified studies should be included or excluded from the Evidence Report. Criteria are overarching as well as specific to each of the KQs.

  Include Exclude
Population KQs 1, 2: Nonpregnant adults age ≥18 years without known vitamin D deficiency

KQs 3, 4: Nonpregnant adults enrolled in studies based on vitamin D deficiency (defined as serum vitamin D levels <30 ng/mL); studies in which 90% of the study population have serum vitamin D levels in the deficiency range will also be included
  • Pregnant women
  • Persons with clinical signs of vitamin D deficiency
  • Studies in which patients are selected for conditions associated with altered vitamin D levels or bone metabolism (e.g., osteoporosis, malabsorption)
  • Studies in which patients are selected for a specific clinical condition to assess the benefit of adding vitamin D to existing treatment (e.g., depression, diabetes, chronic kidney disease, infertility, multiple sclerosis)
Intervention KQs 1, 2: Screening with serum 25-hydroxyvitamin D assay

KQs 3, 4: Treatment with oral or injectable vitamin D2 or D3, with or without calcium

 KQs 1, 2: Vitamin D−binding protein; 1,25-dihydroxycholecalciferol assay

KQs 3, 4: Food-based interventions; vitamin D analogs, multivitamins that include a vitamin D component, sun, or ultraviolet exposure
Comparison KQs 1, 2: No screening

KQs 3, 4: Placebo or no treatment, or usual care

 KQs 1, 2: Head-to-head comparisons of different serum vitamin D assays

KQs 3, 4: Head-to-head comparisons of vitamin D doses or formulations
Outcomes KQs 1, 3:
  • All-cause mortality
  • Incidence of falls
  • Incidence of fractures
  • Incidence of diabetes, cardiovascular disease, and cancer
  • Quality of life, as measured by validated instruments
  • Patient-reported physical functioning, as measured by validated instruments

KQ 2: Anxiety and labeling

KQ 4: Toxicity, renal harms (e.g., nephrolithiasis), and other adverse events

 KQs 1, 3: Changes in serum vitamin D levels, intermediate physiologic outcomes (bone mineral density, osteoporosis, blood pressure, cholesterol, glucose, muscle mass), behavioral outcomes (changes in diet or physical activity), or physical fitness/muscle strength measures (e.g., grip strength, timed up and go test, distance walked test, step test, balance test)

KQs 2, 4: None
Timing KQ 1: Outcomes measured at 8 weeks or longer after screening

KQs 2, 4: Any duration and any timing of measurement

KQ 3: Duration of treatment intervention of at least 8 weeks; outcomes measured at 8 weeks or longer after start of treatment

 KQ 1: Outcomes measured at less than 8 weeks after screening

KQs 2, 4: None

KQ 3: Duration of treatment intervention of less than 8 weeks or outcomes measured at less than 8 weeks after start of treatment
Settings
  • Countries categorized as “very high” on the 2016 Human Development Index (as defined by the United Nations Development Programme)
  • Primary care settings and settings generalizable to primary care
  • Institutional settings (e.g., nursing homes)
 Countries categorized as less than “very high” on the Human Development Index
Study design KQs 1, 3: CCTs, RCTs, and nested case-control studies within RCTs; systematic reviews of CCTs or RCTs with a similar scope to this review

KQs 2, 4: CCTs, RCTs, cohort studies, case-control studies, and systematic reviews with a similar scope to this review

 Editorials, narrative reviews, letters to the editor, and study designs not listed as specifically included (e.g., case reports, case series, studies without a comparison group)
Language English language Languages other than English
Study quality Good- and fair-quality studies (i.e., studies with low risk of bias or some concerns for bias) Poor-quality studies (i.e., studies with high risk of bias)

Abbreviations: CCT=controlled clinical trial; RCT=randomized, controlled trial.