Abstract
Vitamin A deficiency (VAD) occurs in obesity and may be associated with thyroid dysfunction. We aimed to investigate the association of VA with thyroid function in obesity and after laparoscopic sleeve gastrectomy (LSG). Nine hundred and seventy-six obese subjects were enrolled for this study and were divided into VAD, marginal vitamin A deficiency (MVAD), and vitamin A normal (NVA) groups. VAD was defined as VA ≤ 200 ng/ml, MVAD was defined as VA > 200 but <300 ng/ml, and NVA was defined as VA ≥ 300 ng/ml. Thyroid function was compared among groups and the relationship of VA and thyroid function was analyzed. Two hundred and forty-four of the 976 obese subjects underwent LSG, and the change in thyroid function and VA at 3, 6, and 12 months after surgery was measured. Results showed that 37% of all the subjects had subclinical hypothyroidism (SH), and the SH group had lower VA levels than the non-SH group (P = 0.008). Forty-nine percent of all the subjects had MVAD, 9% had VAD, while the MVAD or VAD group had lower FT4 than the NVA group (P = 0.005 and P = 0.001). The VAD group also had higher TSH than NVA group (P = 0.037). VA was significantly negatively associated with TSH (r = −0.151, P = 0.006) and positively associated with FT4 (r = 0.228, P < 0.001). TSH was significantly decreased at 3, 6, and 12 months (3M: from 4.43 ± 2.70 to 2.63 ± 1.46 mU/l, P < 0.001; 6M: from 4.43 ± 2.70 to 3.84 ± 2.34 mU/l, P = 0.041; 12M: from 4.43 ± 2.70 to 2.85 ± 1.68 mU/l, P = 0.024). After LSG surgery, VA levels were slightly increased, when compared to pre-surgery levels, at 3, 6, and 12 months (3M: from 262.57 ± 68.19 to 410.33 ± 76.55 ng/ml, P = 0.065; 6M: from 262.57 ± 68.19 to 281.36 ± 93.23 ng/ml, P = 0.343; 12M: from 262.57 ± 68.19 to 300.37 ± 86.03 ng/ml, P = 0.083). SH group also had lower TSH and higher VA than the non-SH group at 3 months post-surgery [TSH: −1.4(−2.3, −0.3) vs. −0.2(−0.8, −0.2) mU/l, P < 0.001; VA: 163.99 ± 32.58 vs. 121.69 ± 27.59 ng/ml, P = 0.044]. In conclusion VA, which is related to thyroid hormone production, protects against thyroid dysfunction in obese subjects. The improvement of thyroid function in subjects with SH after LSG may be related to the increased VA levels observed post-surgery.Clinical Trial RegistrationClinicalTrial.gov ID: NCT04548232.
Highlights
With changes in human lifestyle and environment, the prevalence of obesity is increasing as caloric intake in excess of caloric expenditure leads to a positive energy balance, obesogenic environment, and expression of genetic factors associated with poor nutrition [1]
fasting plasma glucose (FPG), fasting insulin (FINS), and HOMA-IR were significantly higher while high-density lipoprotein cholesterol (HDL-C) was significantly lower in the Vitamin A deficiency (VAD) group than the NVA group (P < 0.05; Table 1)
Our study showed that FPG, FINS, and HOMA-IR were significantly higher in VAD obese subjects than NVA obese subjects and vitamin A (VA) levels were significantly negatively associated with FPG
Summary
With changes in human lifestyle and environment, the prevalence of obesity is increasing as caloric intake in excess of caloric expenditure leads to a positive energy balance, obesogenic environment, and expression of genetic factors associated with poor nutrition [1]. Obese individuals are predisposed to glucose and lipid disorders as well as vitamin deficiency [2]. VA has some influence on energy metabolism as it has been reported that rats fed a VA deficient diet exhibit increased adiposity and weight gain [5, 6]. Obesity has been significantly related to thyroid hormone dysfunction [7, 8]. The metabolism of thyroid hormone requires iodine but is influenced by micronutrients such as VA [9]. Vitamin A deficiency (VAD) affects the synthesis of thyroglobulin, pairing of iodotyrosine residues to form T4 and T3 and reduces thyroid iodine uptake [10, 11], while VA supplementation reduced thyroid stimulation by thyrotropin and decreased the rate of goiter [12]. No study focuses on the association of VA and thyroid dysfunction in obese individuals
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