Serum TSH, 25(OH) D and phosphorus levels predict weight loss in individuals with diabetes/prediabetes and morbid obesity: a single-center retrospective cohort analysis

BACKGROUND: To evaluate the association of vitamin D and thyroid-stimulating hormone (TSH) with weight loss (WL) percentage (%) in patients with diabetes/prediabetes and Class II/III obesity. METHODS: A retrospective cohort study was designed. Data were collected from a database of a referral endocrinology clinic that is prospectively and systematically generated. After exclusion of unavailable cases, the study enrolled 285 patients (51 ± 11 years old, female/male = 208/77; diabetes/prediabetes = 159/126; no/on levothyroxine replacement = 176/109; Class II/III obesity = 184/101, respectively) who maintained euthyroidism and were followed up for ≥6 months. The data were analyzed to determine the predictors of WL%. RESULTS: Compared with baseline, in the median 22 months of follow-up, the whole study group lost 5.1% of their baseline body weight. As most obesity management trials define success as ‘at least 10% of WL compared to baseline’, we stratified the patients based on WL% extents. The distribution was as follow: Group 1 (n = 61) lost ≥10% body weight, Group 2 (n = 162) lost < 10% body weight, while Group 3 (n = 62) gained weight by the final visit. In groups 1 and 2 (weight losers), the serum thyroid stimulatig hormone (TSH) and parathyroid hormone (PTH) levels decreased and the free thyroxine (fT4), calcium, phosphorus, and 25-hydroxyvitamin D (25(OH)D) levels increased. In Group 3 (weight gainers), these changes were not observed (except for an increase in calcium levels). Regression analysis revealed that the final visit TSH (β = − 0.14, p < 0.05), 25(OH) D (β = 0.15, p < 0.05), and phosphorus (β = 0.20, p < 0.05) levels predicted WL%. However, if patients with autoimmune thyroiditis were excluded from the analysis, the decrease in TSH levels was not statistically significant. CONCLUSIONS: Serum TSH, phosphorus, and 25(OH) D levels predict WL% in euthyroid patients with diabetes/prediabetes and morbid obesity. TSH predictivity seems to be a function of thyroid autoimmunity present with increased frequency in this cohort. Greater levels of phosphorus within the reference range and a sufficient vitamin D status are associated with a greater WL%. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12902-022-01202-4.