Efficacy of Oral Vitamin D Supplementation in Adolescents and Young Adults.

This study assesses whether oral supplementation with vitamin D contributes to the reduction of body mass index and lipid profile in adolescents and young adults. The intervention group will receive 1000 IU of vitamin D (DV) and the control group 200 IU of DV.

Sample size: the simple size was calculated considering the following parameters: an expected difference in the study outcomes (overweight, obesity, and alteration of the lipid profile) of 20% between the intervention group and the control group; a power of 90%, an alfa of 5%, an intervention group/control group ratio of 1:1, and a 20% adjustment for losses to follow-up, resulting in a sample of 270 participants (n=135 intervention and n=135 control group). The OpenEpi software was used for the calculation. Since this is a pilot study and considering the feasibility, the research team decided on a sample size of 150 participants (n=75 intervention group and n=75 control group).

Randomization and blinding: the randomization process will take place in two stages. An engineer from the data central will conduct the randomization of the list of the 217 potentially eligible participants by means of a computer program with random numbers and it will select 150 individuals to participate in the study. Subsequently, a nurse will make phone calls to schedule appointments and formalize the participation in the study, the signature of the informed consent, and the taking of baseline measures. Once these stages are concluded, the assignment of treatment in real time will be made with the support of a computer program. The procedure will take place by means of a single assignment sequence that determines the assignment code for each participant's treatment.

Supplements will be packaged in individual packages with the total number of doses per participant (105 doses). The coding of the packages will be in charge of the laboratory in charge of providing the supplements, which in turn will send to the designated person at the data center by institutional e-mail, a document with the list of codes and the dose of the supplement. The 1000 IU and 200 IU doses of VD will be provided in white containers and will be identical in terms of physical and organoleptic characteristics, to ensure that both participants and investigators are blinded to the treatment. To maximize adherence to the intervention, participants will be required to cross out daily supplementation on a calendar with the study period, which participants should return at the end of the study.

The results of the assignment will only be known by the systems engineer at the data center. In other words, this information "will not be visible" to the coordinating nurse, laboratory personnel in charge of processing biological samples, pediatrician, principal investigator of the study, or the epidemiologist in charge of quality control and data analysis. This will ensure the masking of the people in charge of measuring the outcomes, administering the intervention and analyzing the study data.

Recruitment: for recruitment, a study nurse in charge of enrollment will contact by phone the 217 successful participants of the third re-contact, explain the objective of the study and inquire about the interest to participate; if there is a positive response, inclusion and exclusion criteria will be verified. A list of eligible participants will be generated from the above process and sent to the person in charge of the randomization process.

After the randomization process, the study nurse will receive from the data center the list of the 150 participants selected, who will be invited to participate in the clinical trial. The nurse will call them on the pone for a face-to-face appointment where the details of the study will be informed, doubts will be clarified, and the informed consent form will be signed; a copy of the form will be given to the participant.

During that appointment, the collection of demographic and clinical data will take place, as well as a blood simple for further measurement of VD, lipid profile and glycaemia; The anthropometric nutritional, dietary and physical activity assessment will also be carried out. Once the baseline measurements are taken, the assignment to the intervention will be made in real time through software designed for the study.

Finally, the supplementation intervention will be explained in detail and the package corresponding to the participant's code will be delivered according to the process of assignment to the group (intervention/control), it will be clarified that the supplementation will last 15 weeks and then the second meeting will be scheduled to carry out again the measures taken at the beginning of the study. At the end, a third meeting will be scheduled for the delivery of results and recommendations.

Ethical considerations: the research will be carried out following the principles established in the Good Clinical Practice in Clinical Trials GPC/ICH. It is considered a minimum risk study according to resolution 008430 of October 4, 1993 of the Colombian Ministry of Health, since it includes the administration of a commonly used vitamin supplement with a wide therapeutic margin and for its administration the indications, doses and routes of administration established by the Institute for Drug and Food Surveillance (Invima, acronym in Spanish) are considered.

The vitamin supplement is supplied by the laboratory Farma de Colombia, commercially known as Farma D, whose presentation is in soft gelatin capsules and with registration number 2017 M-0012231-R1.

The processing of personal and clinical data and biological samples will be handled according to the Habeas Data Act (Act 1266 of 2008) of the government of Colombia.

The study was reviewed and endorsed by the Technical Scientific Committee (CTC) of Fundacion Cardiovascular de Colombia (FCV) according to minute N°133 of May 2018 and has the approval of the Research Ethics Committee (IEC) of the FCV according to minute N°480 of July 16, 2019.

The study nurse will explain the objectives, importance, risks, benefits of the research and the confidentiality of the data. Written informed consent will be given to study participants.

Statistical analysis : an analysis will be made by intention to treat. The description of the categorical variables will be made by means of absolute and relative values. Quantitative variables that present a normal distribution in Shapiro Wilk's test will be reported as mean and standard deviation, otherwise the median and interquartile range will be presented. The comparison of the basal characteristics of the study groups (intervention and control) will be done using the ratio comparison test (Chi-square or Fischer's exact test) and the Student's t-test or Mann-Whitney's U-test.

Quantitative outcome variables will be contrasted through paired t-tests or Wilcoxon tests for quantitative variables, methods of longitudinal data analysis will also be explored and for categorical ones the Mc Nemar test will be used. Statistical significance will be considered for all hypothesis tests when the p value is less than 0.05.

Eligibility Criteria:
Inclusion Criteria:

* Belonging to the SIMBA cohort.
* Age ≥ 18 years.
* Re-contact consent from previous studies.

Exclusion Criteria:

* Medical diagnosis of diabetes mellitus, clinically manifest endocrinopathies, acute or chronic infectious liver disease, and kidney disease.
* Adolescents or Young adults subject to treatment with steroids or hormones (except levothyroxine) up to one month before lab sample taking.
* Current supplementation with VD (any form).