To investigate the effect of bariatric surgery on thyroid function and the dose of Levothyroxine (LT4) replacement therapy in obesity patients with hypothyroidism.

Relevant literatures were obtained by searching databases including Embase, Cochrane Library, PubMed, Wanfang, CNKI from January 1996 to June 2022. The included studies were evaluated by MINORs item, and meta analysis was conducted by RevMan 5.4 and Stata 17.0 software.

A total of 755 patients were enrolled in 12 cohort studies. Meta analysis showed that bariatric surgery did not affect the postoperative serum TSH and FT4 levels in obesity patients with hypothyroidism (WMD=0.89, 95%CI: -0.53~2.32, P=0.22; WMD=-0.59,95%CI: -1.30~0.12, P=0.10, respectively). However, it can significantly reduce the dosage needed for LT4 replacement therapy in obesity patients with hypothyroidism (WMD=15.24,95%CI: 8.05~22.43, P<0.001). Meanwhile, meta regression analysis found that the chang of LT4 dose was not correlated with the change of BMI (t=0.83, P=0.455).

Bariatric surgery can reduce the dose of LT4 replacement therapy in obesity patients with hypothyroidism without affecting thyroid function, and it is speculated that bariatric surgery can improve the thyroid function of obesity patients with hypothyroidism after surgery.