Effect of Pre- and Postprandial Plasma Glucose Levels on Thyroid Hormones: A Cross-Sectional Study

Background There is not much data regarding the effect of plasma glucose on thyroid hormones. Currently, there is no consensus regarding the timing of blood sample collection for thyroid hormones. Evaluation of the correlation between plasma glucose and thyroid hormones may enhance pathophysiological understanding of postprandial thyroid stimulating hormone (TSH) decline. Objectives To study the effect of pre-and postprandial plasma glucose levels on thyroid hormones. Methodology A cross-sectional study was done among participants aged 18 years and above after obtaining informed consent. Venous blood samples for fasting and postprandial plasma glucose, fasting, and postprandial thyroid profile ((FT3), (FT4), and TSH) were collected. The association was studied using the t-test and chi-square test between groups, while correlation using Pearson's correlation coefficient. A p-value of <0.05 was considered statistically significant. Results Among the 197 participants, 126 (64%) were female and 71 (36%) were male. The mean (± S.D.) of age was 43.74 (± 12.62) years. Mean (± S.D.) postprandial TSH (4.31 μU/ml (± 7.79)) and free T3 (285.52 pg/dl (± 32.46)) were less than the fasting values (4.99 μU/ml (± 7.78)) and (295.84 pg/dl (± 32.56)). The mean (± S.D.) of both fasting and postprandial TSH and free T4 were less in the high plasma glucose group compared to the normal plasma glucose group (fasting state p-values 0.005, <0.0001 & postprandial state p-values 0.016, <0.0001). The correlation between fasting plasma glucose and fasting TSH values (Pearson correlation; r=-0.18; p-value 0.232) was observed across all the plasma glucose ranges. Conclusion There is a significant postprandial decline in TSH levels than the fasting TSH, indicating that there is a plasma glucose-mediated reduction in TSH values.