INTRODUCTION. The relation between thyroid function and depression has long been recognized. However, studies analyzing coexistence of thyroid dysfunction and suicidal behavior still offer contradictory results [1, 2]. Thyroid hormones that may play an important role in suicidal behavior have not been thoroughly investigated in the sample of individuals with comorbid anxiety and mood disorders (AMD).
OBJECTIVE. To identify potential associations between thyroid function and suicide attempts (SA) in individuals with AMD.
METHODS. This study comprised 136 consecutive participants (mean age 42.4±13.1 years; 69% women). Thirty percent (n=40) of the sample was admitted for a suicidal attempt, 37% (n=50) patients with AMD and without SA and 33% (n=46) individuals without history of mental disorders or suicidal behavior (control group). All participants were interviewed for current psychiatric diagnoses and suicidal behavior using the Mini International Neuropsychiatric Interview [M.I.N.I. 7.0.2]. The biochemical blood tests were performed for the concentrations of free thyroxine (FT4), free triiodothyronine (FT3) and thyroid stimulating hormone (TSH). Multivariable logistic regression analyses were used to assess the associations between thyroid hormones parameters and SA.
RESULTS. All participants had serum FT4, FT3 and TSH level within normal range. Patients with AMD and SA were more likely to be younger than patients with AMD only and the control group (36.6 ± 13 years, p<0.001 vs. 41.5 ± 11.9 and 48.6 ± 12.1). There were no significant differences according to gender, BMI, mean values of TSH and FT4 between groups. Patients with AMD and SA had lower FT3 levels in comparison to patients with AMD without SA and the control group (5.24 ± 0.65 pmol/L, p=0.018 vs. 5.65 ± 0.62 and 5.52 ± 0.71). A multivariable logistic regression revealed that patients with AMD and SA were less likely to have higher FT3 levels than patients with AMD without SA (odds ratio = 0.24 (95% CI 0.08–0.71; p=0.010), after adjusting for gender, education, BMI, smoking, and comorbidity of mental disorders. However, no significant difference in thyroid hormone levels were detected between groups.

CONCLUSION. Lower FT3 concentrations, even within the normal reference range, were related to SA in patients with AMD. This finding supports the importance of evaluating FT3 levels in clinical decision-making on suicide risk of patients with AMD.