## 5 Effects of Micronutrient Supplementation on Weight Management and Metabolic Health in Obesity
### Effects of Micromutrient Supplementation on Glucose Homeostasis  
The effects of micronutrient supplementation on selected parameters indicative of glucose homeostasis status are given in Table 5. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Miconutrient**} & \multirow{2}{*}{**Studied Group**} & \multirow{2}{*}{\
\begin{tabular}{c} **Number of** \\ **People** \\ **Included** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **Effect** \\ **Size** \\ \end{tabular} } & \multicolumn{4}{c}{**Measure (95\% Confidence Interval)**} & \multirow{2}{*}{**Reference**} \\  & & & & **FG (mg/dL)** & & **FI (\#IU/mL)** & & \\ \hline \multirow{2}{*}{Vit. A} & Iranian \({}^{\ast}\)OB & \multirow{2}{*}{56} & \multirow{2}{*}{MD} & \multirow{2}{*}{0.5 (\(-\)1.6, 2.7)} & \multirow{2}{*}{-} & \multirow{2}{*}{-} & \multirow{2}{*}{-} & \multirow{2}{*}{-} & [73] \\  & reproductive-aged & & & & & & & \\  & women & & & & & & & \\ \hline \multirow{2}{*}{Vit. D} & Patients with & \multirow{2}{*}{2006} & \multirow{2}{*}{MD} & \multirow{2}{*}{-2.7 (\(-\)7.8, 2.4)} & \multirow{2}{*}{-} & \multirow{2}{*}{-0.1 (\(-\)0.5, 0.4)} & \multirow{2}{*}{\(-0.0\) (\(-\)0.1, 0.1)} & \multirow{2}{*}{[51]} \\  & diabetes & & & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Effects of vitamin and mineral supplementation on glucose homeostasis. The meta-analyses pointed to significant beneficial effects of supplementing Mg, Se, Zn, and Cr, as well as vitamins E, C, and B9, to at least one of the outcomes reported in Table 5, with Cr giving the greatest reduction of fasting glucose (FG; WMD = \(-19.0\) mg/dL), homeostatic model assessment for insulin resistance (HOMA-IR; WMD = \(-1.53\)), and glycated hemoglobin (HbA1C; WMD = \(-0.71\%\)); and Se of fasting insulin (FI; WMD = \(-3.0\) uIU/mL) among the studied micronutrients [60,118]. These values constituted more than 10% of threshold levels considered normal, which are \(<\) 100 mg/dL for FG, \(<\)5.7% for HbA1C [120], \(<\)25 uIU/mL for FI [121], and from \(<\)1.6 to \(<\)3.8 (depending on population) for HOMA-IR [122]; hence, they could be of clinical relevance in mild cases of disturbed glucose homeostasis. Table 5 does not include data on the influence of Ca supplementation on glucose tolerance. This is because the majority of the available studies applied Ca jointly with vitamin D or were concerned with the increase in dairy product intake. Meta-analyses of these studies reported improvements in glycemic control such as the decrease of the HOMA-IR index by a WMD of \(-0.37\) and MD \(-1.21\), respectively [87,123]. Calcium and Mg are both important in the control of insulin secretion. This process requires an influx of Ca that is regulated by extracellular Mg [80,124]. Furthermore, Mg is a cofactor for enzymatic reactions, including glycolysis [125]. The antioxidative properties of vitamins E and C as well as Se and Zn may ameliorate the inflammation of adipocytes that is thought to contribute to insulin resistance [57,97,98,99,115]. Furthermore, the role of selenoproteins in the regulation of cellular functions and of Zn in the insulin-signaling pathway and clearance were mentioned in the literature as important mechanisms that could help to explain the effects of supplementation with these minerals on glucose metabolism [99,126]. On the other hand, Cr is known to enhance the transport of glucose into cells through the trafficking of glucose transporter type 4 (GLUT-4) [127], whereas vitamins B9 and B12 normalize homocysteine levels and in this way contribute to the maintenance of insulin sensitivity [104]. The effects of some of the micronutrients on glucose homeostasis were dose-dependent. The doses recommended in meta-analyses to achieve optimal effects were \(\geq\)4000 IU/day for vitamin D [89], between 400 and 700 mg/day for vitamin E [57], \(\geq\)1000 mg/day for vitamin C [115], \(\geq\)5 mg/day for vitamin B9 [116], 200 ug/day for Se [118], and \(\geq\)30 mg for Zn [119].