Adherence to a Mediterranean Diet and Thyroid Function in Obesity: A Cross-Sectional Apulian Survey

Much research suggests that Mediterranean eating habits and lifestyle contribute to counteract the risk of chronic diseases while promoting longevity, but little information is available on the effects of the Mediterranean diet (Med-Diet) on thyroid function, particularly among overweight/obese subjects. Nevertheless, consistent data reported a slight increase in serum levels of the thyroid-stimulating hormone (TSH) and a higher rate of conversion of thyroxine (T4) to triiodothyronine (T3) in obesity. This cross-sectional study was aimed at investigating the relationship between adherence to the Med-Diet and circulating thyroid hormones in a cohort of overweight/obese subjects from Apulia (Southern Italy). Methods: We studied 324 consecutive outpatient subjects (228 women and 96 men, age range 14-72 years) taking no drug therapy and showing normal levels of thyroid hormones, but complicated by overweight and obesity (body mass index (BMI) ≥ 25 Kg/m²). The PREDIMED (PREvención con DIeta MEDiterránea) questionnaire was cross-sectionally administered to assess the adherence to the Med-Diet, and hormonal, metabolic, and routine laboratory parameters were collected. Results: Higher adherence to Med-Diet was found to be inversely related to free T3 (p < 0.01) and T4 (p < 0.01) serum levels. Considering each item in the PREDIMED questionnaire, people consuming at least four spoonfuls of extra-virgin olive oil (EVOO) per day, as well as those consuming at least two servings of vegetables per day, had lower free T3 levels (p 0.033 and p 0.021, respectively). Furthermore, consuming at least four spoonfuls of EVOO per day was found to be associated to lower free T4 serum concentrations (p 0.011). Multinomial logistic regression models, performed on tertiles of thyroid hormones to further investigate the relationship with Med-Diet, corroborated the significance only for free T4. Conclusion: Increased adherence to the Med-Diet was independently associated to a slightly reduced thyroid function, but still within the reference range for free T3 and T4 serum levels. This first finding in this field opens up a research line on any underlying biological interplay.