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NSUP: Vitamin D (2008)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:

To determine the relationship between serum 25-hydroxyvitamin D [25(OH)D] and a range of oral vitamin D3 supplementation in an African-American female population.

Inclusion Criteria:
  • Healthy
  • Female
  • Post-menopausal (confirmed on the basis of serum follicle-stimulating hormone concentrations over 23mIU per L)
  • African-American (ancestry of the participants was assessed by self-declaration that both parents and three out of four grandparents were African-American)
  • Not receiving hormone-replacement therapy.
Exclusion Criteria:
  • Previous treatment with bisphosphonates or fluoride
  • Use of estrogen, calcitonin, glucocorticoids, androgens, phosphate, anabolic steroids
  • Over 400 IU per day vitamin D six months before entry
  • Previous hip fracture
  • Uncontrolled diabetes
  • Anemia
  • Thyroid disease
  • History of current liver, renal, neurologic or malignant disease
  • Malabsorption or alcoholism
  • History of hypercalciuria, nephrolithiasis or active sarcoidosis
  • Smoking more than 10 cigarettes a day
  • Unexplained weight loss
  • Use of medications known to interfere with calcium or vitamin D absorption or metabolism, such as anti-convulsants; severe osteoarthritis or scoliosis that would interfere with bone density assessment of the spine or hip
  • Participation in weight training or elite athletic training.
Description of Study Protocol:

Recruitment

Long Island community.

Design

Randomized placebo-controlled, double-blinded longitudinal study.

Blinding Used

Yes.

Intervention

  • Participants were randomly assigned to receive either 20mcg per day (800 IU per day) oral vitamin D3 or a matched placebo
  • At the completion of 24 months of supplementation, the dose of vitamin D3 was raised to 50mcg per day (2,000 IU per day) in the vitamin D group and the study continued for an additional year
  • Calcium intake was assessed with a food-frequency questionnaire at each visit and calcium carbonate supplements were given to both active and placebo groups to ensure a total daily intake of 1,200mg to 1,500mg calcium.

Statistical Analysis

  • Paired T-test
  • Pearson’s coorelation
  • Mixed-model analysis of variance.
Data Collection Summary:

Timing of Measurements

The following tests were done at zero, three, six, 12, 18, 24, 27, 30 and 36 months:

  • Food frequency questionnaire
  • Fasting blood sample (including serum chemistries, calcium, serum parathyroid hormone, 1,25-dihydroxyvitamin D, osteocalcin and cross-laps)
  • 24-hour urine excretion.

The following test was performed at zero, six, 12, 24, 30 and 36 months: Body fat, using Dual-Energy X-ray Absorptiometry.

Dependent Variables

Serum 25-hydroxyvitamin D concentrations.

Independent Variables

Oral vitamin D3 supplementation.

Description of Actual Data Sample:
  • Initial N: 208
    • Placebo Group: 104
    • Vitamin D Group: 104.
  • Attrition: Not described
  • Age
    • Placebo Group: 61.2±6.3
    • Vitamin D Group: 59.9±6.2.
  • Ethnicity: African-American
  • Anthropometrics
    • Placebo Group: 30±4
    • Vitamin D Group: 29±4.
  • Location: Winthrop University Hospital, Mineola NY.
Summary of Results:

Vitamin D Group

  • First three months at the dose of 20mcg vitamin D3 per day
  • Significantly increased the concentration of serum 25-hydroxyvitamin D (P<0.0001)
  • Significant decrease in PTH (P<0.0001).

Effects of the Season

Vitamin D was significantly lower during the summer months: 50.5.8±18.6nm per L (P=0.12)

Author Conclusion:
  • Higher amounts than the recommended upper daily allowance of 50mcg per day (2000 IU per day) may be required to achieve concentrations of 25(OH)D over 75nmol per L in most of the African-American population
  • This study showed that at dose of 50mcg per day can raise the population serum 25(OH)D concentration to an average of approximately 75nmol per L.
Funding Source:
Government: NIA, NIH
Reviewer Comments:
  • Limited presentation of demographic data
  • No power calculation presented
  • No description of diet composition
  • No data presented on baseline serum chemistries, calcium, serum parathyroid hormone, 1,25-dihydroxyvitamin D, osteocalcin and cross-laps.
Quality Criteria Checklist: Primary Research
Relevance Questions
  1. Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies) Yes
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? Yes
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? Yes
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) Yes
 
Validity Questions
1. Was the research question clearly stated? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? Yes
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? Yes
2. Was the selection of study subjects/patients free from bias? Yes
  2.1. Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study? Yes
  2.2. Were criteria applied equally to all study groups? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? Yes
  2.4. Were the subjects/patients a representative sample of the relevant population? Yes
3. Were study groups comparable? Yes
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) Yes
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? Yes
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) Yes
  3.4. If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis? N/A
  3.5. If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.) N/A
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? N/A
4. Was method of handling withdrawals described? Yes
  4.1. Were follow-up methods described and the same for all groups? Yes
  4.2. Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.) Yes
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? Yes
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? Yes
5. Was blinding used to prevent introduction of bias? Yes
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? Yes
  5.2. Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.) Yes
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? N/A
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? N/A
  5.5. In diagnostic study, were test results blinded to patient history and other test results? N/A
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? Yes
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? Yes
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? Yes
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? Yes
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? Yes
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? Yes
  6.6. Were extra or unplanned treatments described? Yes
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? Yes
  6.8. In diagnostic study, were details of test administration and replication sufficient? Yes
7. Were outcomes clearly defined and the measurements valid and reliable? Yes
  7.1. Were primary and secondary endpoints described and relevant to the question? Yes
  7.2. Were nutrition measures appropriate to question and outcomes of concern? Yes
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? Yes
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? Yes
  7.5. Was the measurement of effect at an appropriate level of precision? Yes
  7.6. Were other factors accounted for (measured) that could affect outcomes? Yes
  7.7. Were the measurements conducted consistently across groups? Yes
8. Was the statistical analysis appropriate for the study design and type of outcome indicators? Yes
  8.1. Were statistical analyses adequately described and the results reported appropriately? Yes
  8.2. Were correct statistical tests used and assumptions of test not violated? Yes
  8.3. Were statistics reported with levels of significance and/or confidence intervals? Yes
  8.4. Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)? Yes
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? Yes
  8.6. Was clinical significance as well as statistical significance reported? Yes
  8.7. If negative findings, was a power calculation reported to address type 2 error? N/A
9. Are conclusions supported by results with biases and limitations taken into consideration? Yes
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? Yes
10. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes