Plain English Summary
Background and study aims
Hypovitaminosis D (a deficiency in Vitamin D, a nutrient that comes from sunlight) has been associated with anemia in patients with chronic diseases and also in healthy populations. One of the explanations for this association is the action of vitamin D on iron metabolism, which influences the absorption and mobilisation of iron, mainly through inflammatory mechanisms. It is not yet known if vitamin D could directly influence the body iron storage. The aim of this study was to verify the correlation between vitamin D levels and body iron store in a population of healthy adult women.
Who can participate?
Women aged 18 and older with chronic diseases.
What does the study involve?
Participants are measured for their body iron content and their vitamin D levels measured which is retrieved from a public database. The data is then analysed using a statistical model.
What are the possible benefits and risks of participating?
There are no benefits or risks with participating.
Where is the study run from?
Instituto De Medicina Integral Professor Fernando Figueira (Brazil)
When is the study starting and how long is it expected to run for?
November 2016 to December 2016
Who is funding the study?
Investigator initiated and funded (Brazil)
Who is the main contact?
Mrs Daneily Barbosa
danycariry@hotmail.com
Trial website
Contact information
Type
Public
Primary contact
Mrs Daniely Barbosa
ORCID ID
Contact details
Rua Arlindo Gouveia
145
2502b
Recife
50720595
Brazil
+55 819 883 73784
danycariry@hotmail.com
Additional identifiers
EudraCT number
ClinicalTrials.gov number
Protocol/serial number
Plataforma Brasil. CAAE: 60849916.3.0000.5201
Study information
Scientific title
Influence of vitamin D on body iron store in healthy women from NHANES: a cross-sectional study using an econometric model of causal inference
Acronym
Study hypothesis
Hypotheses:
1. Vitamin D levels have a positive correlation with body iron content in women.
2. Positive correlation functions between vitamin D levels and body iron content differ according to age, race, menstrual status and levels of parathyroid hormone.
3. Vitamin D has a cause-effect relationship on body iron content.
Ethics approval
Ethics Committee on Research in Human Beings of the Institute of Integral Medicine, 05/12/2016, ref: Record number: 60849916.3.00005201
Study design
A cross-sectional population-based study
Primary study design
Observational
Secondary study design
Cross sectional study
Trial setting
Community
Trial type
Other
Patient information sheet
No participant information sheet available.
Condition
Hypovitaminosis D and iron deficiency
Intervention
The study is cross-sectional study. Participants have the variables of interested measured. This includes measurements for body iron content (calculated using Cook's formula) and 25hydroxivitamin D levels. There is no follow up. The data is retrieved from NHANES public datasets, which includes laboratory information of interest: levels of RsTf (soluble transferrin receptor), ferritin and 25hydroxivitamin D. No sample size calculation was performed, choosing to use all the observations that met the selection criteria in the years 2003-2004 and2005-2006.
Statistical analysis:
A predictive multivariate theoretical model, with Body Iron Store as dependent variable and 25 hydroxivitamin D as the predictive variable is designed. Statistical strategy to select covariables is not used, choosing, instead, saturated models that aim to estimate the coefficient of the predictive variable adjusted for the largest possible number of confounders. The following confounding covariables are: age, race, educational level, annual family income (USD/year), menstrual status, body mass index (BMI) (kg/m2), albumin level (g/dL), CRP level (mg/dL) and parathyroid hormone (PTH) level (pg/mL).
Initially, a simple linear regression model (Ordinary Least Squares – OLS) is used to evaluate the β coefficient of the correlation between 25OHD and BIS, which is then adjusted for sociodemographic, clinical, and laboratory covariables in a multiple linear regression model. For the evaluation of the possible effect modifiers, the model was stratified according to the subgroups of iron-sufficient and iron-deficient women. Next, vitamin D interaction terms, with age, race, PTH and menstrual status, are added, which are included in the multivariate models as products of 25OHD and each of these covariables.
Then, to access causal inference, we chose the econometric model proposed by Lewbel to identify the effect of endogeneity on dose-response correlation coefficients. According to the econometric rationale, if we can mathematically rule out the endogeneity bias, we can perform a causal inference.
Intervention type
Other
Phase
Drug names
Primary outcome measure
Vitamin D levels in correlation with body iron stores (BIS) are measured using patient data and a predictive model.
Secondary outcome measures
There are no secondary outcome measures.
Overall trial start date
01/11/2016
Overall trial end date
31/12/2016
Reason abandoned (if study stopped)
Eligibility
Participant inclusion criteria
1. Women older than 18 years old
2. Who did not have chronic diseases
3. In whom the results of 25-hydroxyvitamin D (25OHD)
4. Soluble transferrin receptor (sTfR)
5. Ferritin levels available
6. Chronic diseases as defined as the following a self-report of cancer, heart failure, pulmonary emphysema, chronic bronchitis, gastric or intestinal diseases; changes in laboratory markers of liver disease (aspartate aminotransferase greater than 121 U/L, alanine aminotransferase greater than 128 U/L and total bilirubin greater than 2.1 mg/dL) or renal disease (creatinine greater than 1.5 mg/dL); and the presence of a HIV-positive serology.
Participant type
Healthy volunteer
Age group
Adult
Gender
Female
Target number of participants
3667
Participant exclusion criteria
1. Women who reported undergoing iron supplementation in the last 3 months
2. Who had a positive pregnancy test or changes in the markers of malnutrition (albumin < 3.5 g/dL)
3. Inflammation (C-reactive protein (CRP) > 5.0 mg/dL) or iron overload (transferrin saturation > 45%)
Recruitment start date
01/01/2017
Recruitment end date
31/08/2017
Locations
Countries of recruitment
United States of America
Trial participating centre
Instituto De Medicina Integral Professor Fernando Figueira
R. dos Coelhos, 300 - Boa Vista
PE
Recife
50070-550
Brazil
Funders
Funder type
Other
Funder name
Investigator initated and funded
Alternative name(s)
Funding Body Type
Funding Body Subtype
Location
Results and Publications
Publication and dissemination plan
Planned publication of the results in the American Journal of Clinical Nutrition.
IPD sharing statement:
The datasets generated during and/or analysed during the current study are/will be available upon request from Daniely Sobreira Cariry Barbosa (danycariry@hotmail.com)
Intention to publish date
30/09/2017
Participant level data
Available on request
Basic results (scientific)
Publication list