Magnesium nutritional status and its relationship to metabolism of thyroid hormones in obese women

Objective: To evaluate the magnesium nutritional status and its relationship to thyroid hormones in obese women. Methods: Cross-sectional study involving 177 women, aged between 20 and 50 years, distributed in two groups: obese women, n = 73, and normal weight women, n = 104. The analysis of magnesium intake was performed using the three-day food registry using Nutwin version 1.5. Plasma, erythrocyte and urinary magnesium concentrations were determined using the inductively coupled plasma optical emission spectrometry method. Serum concentrations of thyroid hormones were determined by chemiluminescence. Data were analyzed using the statistical software SPSS for Windows 25.0. Results: Obese women had reduced plasma and erythrocyte magnesium concentrations when compared to the control group (p<0.05). The urinary excretion of this mineral presented a significant difference between the groups (p<0.05). Serum concentrations of T3 and T3/T4 ratio showed a statistically significant difference between the groups (p< 0.05), with lower values in obese women. There was a negative correlation between erythrocyte magnesium and serum free T4 (p<0.05), between dietary magnesium and T3/T4 ratio (p<0.05), and positive correlation between plasma magnesium and serum TSH (p<0.05). Conclusion: Given the negative correlation between magnesium concentrations in erythrocytes and T4 levels, this study does not show a possible role of the mineral in the metabolism of this hormone. Thus, it is suggested a probable impairment in the action of magnesium on the absorption of iodine by thyroid cells, as well as the probable interference of other biochemical factors during the process of metabolizing its precursor, TSH, which reflects negatively on the synthesis of the T4 hormone.