Ferrannini et al. found that fT3/fT4 ratio negatively correlated with insulin sensitivities determined by insulin-clamp in 940 non-diabetic patients with normal thyroid function [38], while Park et al. found that fT3/fT4 ratio corelated with metabolic syndrome parameters and insulin resistance in 132,346 subjects who underwent medical health check-up programs [39]. Here, INS is linked to metabolic syndrome.