Correlation between Body Mass Index and Thyroid Function in Euthyroid Individuals in Greece

Although the effects of hypothyroidism and hyperthyroidism on body weight have been clearly demonstrated, there is no sufficient data on the relationship between the body mass index (BMI) and minor differences within the normal range of thyroid function. The present study aims to investigate the relationship of fluctuations of the thyroid stimulating hormone (TSH) and thyroid hormones with BMI in euthyroid subjects. The study included 736 euthyroid healthy individuals of known age, weight, height, and biochemical picture of the thyroid function. Individuals were classified according to BMI and thyroid hormones’ values. The variations of normal thyroid function in euthyroid individuals were associated with body weight changes. A statistically significant positive correlation between BMI and thyroid function in women was found, while in men the correlation was not statistically significant. The alterations in thyroid function are mainly primary, while changes in body weight are secondary. The reason may be simple or multifactorial, and the biological mechanism is not completely known. Finally, the thyroid function disorders in conjunction with the strong influence of various environmental factors can increase body weight and lead to obesity.