Serum Fibroblast Growth Factor 21 Levels in Patients with Hyperthyroidism and its Association with Body Fat Percentage

BACKGROUND: Most of the actions of thyroid hormone (TH) on body metabolisms like maintenance of basal metabolic rate (BMR) and body fat are similar to that of fibroblast growth factor 21 (FGF21). We hypothesized that in patients with hyperthyroidism, the pathological changes in the BMR, body fat are mediated by TH through FGF21. OBJECTIVES: To study the association of serum FGF21 levels with hyperthyroidism and correlate body fat percentage with serum FGF21 levels in hyperthyroid patients. STUDY DESIGN: Case-control prospective follow-up study. METHODOLOGY: A total of 68 hyperthyroid patients and age, sex-matched healthy controls who fulfilled the inclusion and exclusion criteria were studied. Among them, 45 cases were followed up at 3 to 6 months after the achievement of euthyroidism. Body fat percentage was calculated from Jackson and Pollock 3 site equation and Siri equation. BMR percentage was calculated by the Gale formula. RESULTS: The mean age in years in the cases was similar to that of controls (36.14 ± 10.01 vs. 36.57 ± 10.53, P = 0.81). The serum FGF21 levels at baseline were significantly elevated in patients with hyperthyroidism compared to controls [median 406.6 pg/ml (interquartile range, 262.9–655.6) vs. 252.3 (125.1–341) P < 0.001] and declined dramatically following treatment with anti-thyroid drugs [405 (275.5–680.4) vs. 203.6 (154.6–230.6) P < 0.001]. Serum FGF21 levels negatively correlated with body fat percentage (r = –0.268, P = 0.002). After adjusting to various confounding factors, serum FGF21 was independently associated with hyperthyroidism and was significant. (OR [95%CI] 3.78 (1.046–13.666) P = 0.043). CONCLUSION: Serum FGF21 levels were elevated in hyperthyroid patients and decreased following treatment with anti-thyroid drugs. It was independently associated with hyperthyroidism. There may be a future therapeutic role of FGF21 inhibition in the reversal of these changes in addition to anti-thyroid drugs in patients with hyperthyroidism.