Relationships of low serum vitamin D3 with anthropometry and markers of the metabolic syndrome and diabetes in overweight and obesity

Relationships of low serum vitamin D3 with anthropometry and markers of the metabolic syndrome and diabetes in overweight and obesity

Conversion of vitamin D3 to its derivative 1,25 vitamin D3 is complex and involves other hormones. 1,25 vitamin D3, via its receptor which is present in insulin-producing beta-islet cells, is known to be a potent regulator of cell proliferation and differentiation [22,23]. However, there is evidence that low vitamin D3 itself is associated with TIIDM irrespective of 1,25 vitamin D3 [8]. The inverse relationship of vitamin D3 with high to extreme HbA1c [24,25] and/or FPG [7,8] may indicate that it is the long-term, severely abnormal (carbohydrate) metabolism of TIIDM [7,26,27] and muscle insulin resistance [28], that is associated with hypovitaminosis D3. HbA1c, a glycated protein, is a predictor of 2-hour glucose in oral glucose tolerance testing, [29] an indicator of chronic hyperglycaemia, protein glycation damage [30] and oxidative stress [31]. Many new, profound and interacting mechanisms link hypovitaminosis D with other correlates of the metabolic syndrome, including renin regulation [1]. Vitamin D-upregulated protein-1 reportedly modulates endothelial oxidative stress, macrophage and smooth muscle function, depending on the stage of atherosclerosis [32,33].
Limitations of the present study include the cross sectional design where cause cannot be attributed. Lifestyle, body shape sensitivity [34,35] or cultural reasons [36] for precluding skin exposure to view, and ultraviolet light for efficient vitamin D3 synthesis, may selectively affect obese people but were not examined.
In the current study low serum vitamin D3 was inversely related to weight and BMI, but not fat mass, and to markers indicative of TIIDM (large waist and raised HbA1c), rather than MetSyn per se. The link between hypovitaminosis D3 and metabolic disorders, including obesity, MetSyn, TIIDM and CVD requires further investigation, particularly for those most at risk of these combined conditions.