Chrononutrition variables and thyroid function: evidence for a specific role of the time of the first meal

The aim of this study was to examine the associations between chrononutrition variables (time of first meal, time of last meal, and eating window) and thyroid function.

A cross-sectional study was conducted among 608 healthy adults aged ≥ 18 years. Chrononutrition variables were collected through a face-to-face interview. Fasting blood samples were collected to measure serum thyroid-stimulating hormone (TSH), free triiodothyronine (FT3), and free thyroxine (FT4) levels. Multiple linear regression analyses were used to evaluate associations between chrononutrition variables and thyroid hormones.

Among 608 healthy adults, later timing of the first meal was associated with higher TSH levels. In the fully adjusted model, participants who had their first meal after 08:30 had higher TSH levels than those who had their first meal at or before 07:30 (β = 0.56, 95% CI: 0.07 to 1.06; P trend = 0.02). In contrast, the time of last meal after 19:00 was not significantly associated with TSH levels (β = -0.07, 95% CI: -0.66 to 0.53; P trend = 0.63). An eating window longer than 11 h was also not significantly associated with TSH levels (β = -0.45, 95% CI: -0.97 to 0.08; P trend = 0.09). No significant associations were observed between the chrononutrition variables and FT3 or FT4 levels.

Our study suggested that the time of first meal, rather than the time of last meal or eating window, may be particularly relevant for TSH regulation.