The effect of different amounts of vitamin D supplementation on serum calcidiol, anthropometric status, and body composition in overweight or obese nursing women: a study protocol for a randomized placebo-controlled clinical trial

BACKGROUND: The optimal vitamin D intake for nursing mothers with overweight or obesity has not been defined. Vitamin D concentrations are associated with body composition indices, particularly body fat mass. Few studies have investigated the relationship between hypovitaminosis D, obesity, anthropometric status, and body composition in nursing women. Thus, the present study aims to investigate whether vitamin D supplementation during lactation will improve vitamin D status, reduce body fat mass, and improve body composition. METHODS/DESIGN: In a double-blind, randomized, placebo-controlled, parallel-group trial, after term delivery, 90 healthy women with overweight or obesity will be selected and randomly allocated into three groups to receive 2000 IU/d cholecalciferol (vitamin D3), 4000 IU/d cholecalciferol, or placebo (lactose) for 12 weeks while nursing. Measurements of height, weight, waist circumference, and body composition (fat mass (kg), lean mass (kg), body fat (%), fat mass index, and relative fat mass index) will be taken for all subjects at baseline and after 12 weeks of intervention. In addition, serum 25-hydroxyvitamin D (25(OH)D), parathyroid hormone, calcium, and phosphorus will be measured. DISCUSSION: This study is the first investigating the effect of different amounts of vitamin D supplementation on serum calcidiol, anthropometric status, and body composition in nursing women with overweight or obesity. Our findings will contribute to the growing body of knowledge regarding the role of vitamin D supplementation in obesity, anthropometric status, and body composition in nursing women. TRIAL REGISTRATION: Iranian Registry of Clinical Trials IRCT20140413017254N6. Registered on 11 April 2018. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s13063-019-3622-y) contains supplementary material, which is available to authorized users.