Effects of vitamin D supplementation on cardiovascular risk factors in shift workers : study protocol for randomized, double-blind, placebo-controlled clinical trial.

Objective: The present clinical study aims to describe protocol to evaluate the effects of vitamin D3 supplementation on the cardiovascular risk factors in a population of rotating shift workers. Design: A randomized, double-blind, placebo-controlled, parallel group clinical trial testing 2 oral dosages of cholecalciferol (14,000 IU and 28,000 IU per week) for 12 months. Setting: The primary outcome for evaluation is an 18% reduction in hypertriglyceridemia (?150mg/dL) between pre and postintervention measurements. Baseline characteristics of the study population will be summarized separately within each randomized group, and will use tests for continuous and categorical variables. For all tests, a P<.05 will be considered significant. The analysis of primary and secondary outcomes will use an intention-to-treat population and a per-protocol population. The primary and secondary outcomes will be compared separately between each treatment group and placebo, using binary logistic regression or regress?o de Poisson for proportions (for binary outcomes) and using linear regression for differences in means (for continuous endpoints), with 95% confidence intervals. Participants: Rotating shift workers, adults aged between 18 and 60 years, with hypovitaminosis D and alterations in at least 1 of the following parameters: fasting glucose, high-density lipoprotein cholesterol, triglycerides, low-density lipoprotein cholesterol, blood pressure, and waist circumference. Conclusion: This clinical trial aims to contribute to the gap in knowledge about the potential, dose, and time of vitamin D supplementation to generate beneficial effects on triglycerides in a population at increased risk for hypertriglyceridemia and vitamin D deficiency. Abbreviations: 25(OH)D = vitamin D, AUDIT = Alcohol Use Disorders Identification Test, BAI = body adiposity index, BMI = body mass index, C index = conicity index, CI = confidence interval, DMC = data monitoring committee, HDL = high-density lipoprotein, HOMA-IR = homeostatic model for insulin resistance, IPAQ = International Physical Activity Questionnaire, ITT = intention-to-treat, LDL = low-density lipoprotein, MMSE = Mini Mental State Examination, PP = per-protocol, PTH = parathyroid hormone, RR = relative risk, SF-36 = The Medical Outcomes Study 36-Item Short-Form Health Survey, TSC = Trial Steering Committee, WHOQOL = World Health Organization Quality Of Life Instrument, WHR = waist?hip ratio, WHtR = waist?height ratio