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NSUP: Vitamin D (2008)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
  • To study how vitamin D3 supplements at varying doses affect serum 25 hydroxy vitamin D concentrations
  • To determine the lowest vitamin D3 supplement dose to maintain serum 25 hydroxy levels above the insufficiency range
  • To determine which dose is effective in decreasing S-iPTH concentration.
Inclusion Criteria:
  • Women
  • 65 to 85 years old.
Exclusion Criteria:

None disclosed.

Description of Study Protocol:

Recruitment

52 women recruited from an announcement in local Helsinki newspaper.

Design

12-week study included 52 women randomly assigned to four groups:

  • Placebo
  • 5mcg vitamin D3 supplement
  • 10mcg vitamin D3 supplement
  • 20mcg vitamin D3 supplement.

Intervention

Vitamin D3 supplement at either 5mcg per day, 10mcg per day or 20mcg per day.

Statistical Analysis

  • SPSS version 10.0 for Windows
  • Pearson correlation characteristics; the association between variables
  • Repeated-measures of ANOVA was used to study the effects of supplementation at different time-points and differences between groups
  • T-test was used for two group-comparison independent samples
  • Post-hoc tests were performed with Tukey's honestly significant difference and least significant difference
  • The Friedman, Kruskal-Wallis or Mann-Whitney U-test were used if the variables were not normally distributed.
Data Collection Summary:

Timing of Measurements

  • Fasting blood samples collected at baseline and every other week
  • 24-hour urine samples collected at beginning, middle and end of study
  • FFQ and medical history questionnaire were also collected at baseline.

Dependent Variables

Serum 25 hydroxy vitamin D.

Independent Variables

Vitamin D3 supplements.

Description of Actual Data Sample:
  • Initial N: 52
  • Attrition (final N): 49
  • Age: 65 to 85 years
  • Ethnicity: Undisclosed.

Other Relevant Demographics

  Placebo 5mcg 10mcg 20mcg
Age
71
71
72
71
Weight (kg)
67.2
68.9
66.6
71.2
Height (cm)
161.5
163.9
160.9
161.8
Users of HRT
6%
6%
3%
9%
Dietary Intake of Vitamin D (ug/d)
10.9
9.7
10.6
9.7
Dietary Intake of Calcium (mg/d)
946
1,225
911
1,152
S-25-OHD (nmol/L)
52.2
46.0
46.5
44.1

Location

Helsinki, Finland.

Summary of Results:
  • All supplemenation groups had significantly increased serum 25 hydroxy levels (P<0.001)
  • Placebo group serum 25 hydroxy levels decreased
  • A plateau was reached in serum 25 hydroxy levels after six weeks in all the supplementation groups
  • The s-25-OHD concentration increased in the treatment groups beyond the placebo group by two weeks (P<0.001)
  • S-iPTH concentration was not normalized after 12 weeks even at 20- mcg-per-day dose.

  5mcg 10ug 20mcg
Plateau Levels (nmol/L)
57.7
59.9
70.0

Other Findings

  • 15mcg is thought to be adequate to maintain the serum 25 hydroxy levels around 40nmol to 55nmol per L during winter
  • Higher vitamin D3 supplementation dosage may be needed if optimum levels of serum 25 hydroxy are found to be higher
  • Serum 25 hydroxy levels increased quicker in subjects with lower baseline levels
  • Subjects with higher baseline levels reached higher serum 25 hydroxy levels after 12 weeks.
Author Conclusion:
  • 10mcg per day is not enough to keep S-25-OHD above 40nmol per L in winter
  • At 15mcg per day, a S-25-OHD concentration of 40nmol to 55nmol per L is maintained
  • To maintain the summer S-25-OHD concentration of 60nmol per L, the elderly would require on average 24mcg per day of vitamin D.
Funding Source:
University/Hospital: University of Helsinki
Reviewer Comments:
  • Study size was small
  • Study was only 12 weeks long.
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? ???
  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? No
  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? ???
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) No
  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? N/A
5. Was blinding used to prevent introduction of bias? No
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? No
  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.) No
  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? N/A
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? ???
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? ???
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? No
  6.6. Were extra or unplanned treatments described? N/A
  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? N/A
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? ???
  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