Thyroid Dysfunction and the Risk of Clinically Relevant Depression: A Longitudinal Cohort Study

Area of Science:

• Endocrinology
• Psychiatry
• Epidemiology

Background:

• Thyroid function significantly impacts mood and mental health.
• Subtle thyroid dysfunction may be associated with depressive symptoms.
• Longitudinal data is crucial for understanding the temporal relationship between thyroid status and depression.

Purpose of the Study:

• To investigate the association between thyroid function, specifically thyrotropin levels, and the development of clinically relevant depression (CRD).
• To analyze sex-based differences in the incidence and onset of thyroid dysfunction and CRD.
• To assess the risk of CRD in individuals with low or high thyrotropin levels within a longitudinal cohort.

Main Methods:

• A longitudinal cohort study was conducted with 6191 euthyroid adults.
• Thyroid function (thyrotropin levels) and depression (PHQ-9 scores) were assessed over time.
• Cox proportional hazards models were used to evaluate the association between thyroid dysfunction and CRD, considering time-varying covariates and sex differences.

Main Results:

• Thyroid dysfunction was significantly associated with an increased risk of CRD (HR, 1.33; P<.001).
• Both low (HR, 1.57; P<.001) and high (HR, 1.25; P=.005) thyrotropin levels were linked to elevated CRD risk.
• Females exhibited a higher incidence and earlier onset of both thyroid dysfunction and CRD compared to males.

Conclusions:

• Thyroid dysfunction is a significant risk factor for developing clinically relevant depression.
• Females are disproportionately affected, showing earlier and more frequent occurrences of both thyroid dysfunction and depression.
• These findings highlight the importance of screening for depression in individuals with thyroid dysfunction, particularly in females.