Fig. 3
From: Relationship between caffeine intake and thyroid function: results from NHANES 2007–2012
Association between Serum TSH and Caffeine in Group 1. (A): Nonlinear Relationship Evaluation using the RCS Model. (B-D): Relationship between Serum TSH and Caffeine Intake using Piecewise Linear Regression. Adjustments were made for gender, race, age, BMI, drinking and smoking habits, hyperglycemia, hypertension, cardiovascular disease (CVD), cancer, comorbidities, urinary iodine, and intake of micronutrients (selenium, vitamin D, calcium, zinc, iron, magnesium) and macronutrients (protein, carbohydrate, and fat). Caffeine, TSH, urinary iodine, and micronutrient intake were log-transformed. A total of 12 subjects were excluded from regression due to missing data in cancer (n = 2) and urinary iodine (n = 10)