**Author details**

**3.5. Volumetric dilution**

150 Adiposity - Omics and Molecular Understanding

size does not fit all" [72].

**4. Conclusions**

to explain the low VD status widely reported in obesity.

system as well as autocrine/paracrine actions of VD.

regulation on AT, especially in obese environment.

**Acknowledgements**

Most recently, Drincic et al. [72] showed that body weight and body fat are inversely correlated with 25(OH)D levels across the spectrum of body weight ranging from normal to obese. This inverse association is related to the greater volume of distribution for both VD3 and 25(OH)D in tissue mass. They suggested that simple volumetric dilution is the most thrifty explanation for the low VD status in obesity. A hyperbolic model best explains the lower 25(OH)D values in obesity, and when serum 25(OH)D values was adjusted for body weight, difference between obese and normal subjects disappeared. These authors went on to recommend that the VD dosing for treatment of VDD in obesity should be based on body weight, for example, "one

Overall, although these are the five most commonly suggested mechanisms, the latter two theories have more robust evidences available. The strong evidence presented for the sequestration and volumetric dilution hypotheses, and more importantly, a lack of contradictory evidence for either, suggest that they are the most probable, independently or in combination,

The prevalence of obesity and VDD is growing exponentially in recent decades, and several studies have been conducted worldwide, particularly, the signs of VDR and hydroxylase enzymes in AT (SAT and VAT). VD is a nutrient with important role in the genesis of obesity and also in diseases associated with chronic inflammation. It features an anti-inflammatory effect in AT, anti-adipogenic activity, exerts immunoregulatory effect, and has the capacity to limit the expression of inflammatory markers in AT. Scientific evidences suggest that AT is a target for VD action, as CYP27B1 and VDR genes that are expressed by adipocytes. All evidence suggests that 25(OH)D, 1,25(OH)2D, and VDR are involved in the AT, through the endocrine

Based on news researches, there is a hypothesis that AT is not only a stock of VD but also has a dynamic ability to activation and deactivation of this vitamin in obesity. Low VD status in obesity may have implications for AT biology based on recent data from different research groups which are converging to highlight the impacts of VD on AT/adipocyte biology. Therefore, some key points have yet to be elucidated in relation to VD metabolism and its

The authors acknowledge the contribution of Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) that provided the payment of publication this book's chapter.

Adryana Cordeiro1,3\* and Andrea Ramalho1,2,3

\*Address all correspondence to: adrynutri@yahoo.com.br

1 Micronutrients Research Center (NPqM), Institute of Nutrition Josué de Castro (INJC) of the Federal University of Rio de Janeiro (UFRJ), Rio de Janeiro, Brazil

2 Social Applied Nutrition Department, Institute of Nutrition Josué de Castro (INJC) of the Federal University of Rio de Janeiro (UFRJ), Rio de Janeiro, Brazil

3 Medical Clinic Program, Faculty of Medicine, UFRJ, Rio de Janeiro, Brazil
