Our results on the seasonal dynamics of FT3 suggest that to understand the causes influencing thyroid hormones in obesity, one must consider not only factors like age, sex, different degrees of obesity, fat percentage, leptin, insulin sensitivity, smoking habits, iodine intake, and hypocaloric diet [124,125,130,135,136,140], but also environmental factors, specifically winter air temperature. This evidence concerns the gene INS and obesity due to melanocortin 4 receptor deficiency.