Discussion
obesity, Hashimoto’s thyroiditis, hypercholesterolemia, FM, hypothyroid, adiposity, thyroid failure
OBESITY, HYPERCHOLESTEROLEMIA, HYPOTHYROID, SUBCLINICAL HYPOTHYROIDISM, ADIPOSITY, VITAMIN D DEFICIENCY, SUBCLINICAL HYPOTHYROIDISM
Subclinical hypothyroidism is often considered an early sign of thyroid failure (According to our results, the mean 25-OH D3 level was lower than normal limits (≥30 ng/ml) (In the current study, in addition to the reduction of TC levels, the lowering effects of vitamin D supplementation were considerable on LDL-C levels. In the study by Ucan et al., 50,000 IU/week of 25-OH-D3 intramuscularly for eight weeks lowered LDL-C after two months in patients with Hashimoto’s thyroiditis (Our results indicate the potential effect of vitamin D supplementation on reducing TC levels. This effect might be mediated partly through the lowered TSH level determined in our intervention group. TSH can decrease phosphorylated HMG-CoA reductase expression via AMPK in the liver, leading to increased HMG-CoA reductase activity and hypercholesterolemia (According to our findings, vitamin D supplementation increased the serum levels of irisin. In the study by Al-Daghri et al. on 78 subjects with vitamin D deficiency who received adequate sunlight and ate vitamin D-enriched foods, irisin levels increased with vitamin D levels (Based on our findings, the elevated serum irisin levels in the vitamin D-supplemented group might be partly involved in the changes in FM % and FFM %. However, no considerable changes were seen in overall and abdominal obesity values, though a longer intervention period for maintaining sufficient vitamin D status might be required to obtain considerable reductions in obesity values. Similarly, in the study by Talaei et al., no significant alterations were observed in the weight and BMI of hypothyroid patients after receiving 50,000 IU/week of vitamin D for three months (It should be noted that in the current study, we did not intervene to make changes in dietary intakes, physical activity levels, and sunshine exposure time in either group during the study. Therefore, these factors were not accounted for as confounding factors in the interpretation of the biochemical and anthropometric variables.The strength of this study is that it was a well-designed controlled clinical trial, eliminating potential sources of bias. However, some limitations existed, including the short study duration, small sample size, and fixed dose of vitamin D. Therefore, the findings of this study may not be generalized to other doses and durations of vitamin D supplementation. Also, our findings are not applicable to patients with low or normal BMIs or men with subclinical hypothyroidism. Further studies are needed to investigate the impact of vitamin D on SIRT1 and adiposity as well as on muscle strength via its effect on irisin levels.