Hypothyroidism Rates Higher in Early- vs Late-Onset Affective Disorders

Early-onset affective disorders may be associated with an increased prevalence of hypothyroidism, investigators reported in the Journal of Affective Disorders.

The cross-sectional study included in-patients who were admitted to the hospital between January 2016 and December 2018 who were diagnosed with bipolar disorder (BD) or major depressive disorder (MDD) and were drug free. “Drug free” was defined as no use of psychiatric drugs for at least 4 months before admission.

The researchers obtained patient data regarding diagnosis, illness duration, and medications prescribed before admission, as well as fasting serum thyroid function measurement results and measurement time.

A total of 5643 patients were included—2024 with BD, 2232 with MDD, and 1387 with schizophrenia (SZ). The participants with SZ were used as a nonaffective disorder group to assess whether the association between age of onset and hypothyroidism was specifically in affective disorders.

Early-onset affective disorder was defined as BD and MDD developed before age 22 years. A subgroup of patients aged <50 years was selected to analyze the association between the age of onset for affective disorders and comorbidity of hypothyroidism.

Patients with BD had a median age of 28 years (8-49), a median onset age of 22 (interquartile range [IQR] 11) years, a median disease duration of 36 (IQR 96) months, and 64.8% were male. Patients with MDD had a median age of 33 years (10-49), a median onset age of 29 (IQR 20) years, a median disease duration of 12 (IQR 44) months, and 42.3% were men. Patients with SZ had a median age of 28 years (IQR 10-49), a median onset age of 22 years (IQR 11), a median disease duration of 48 (IQR 90) months, and 45.2% were men..

Patients with early-onset affective disorders had higher rates of hypothyroidism vs late-onset patients (BD, 9.4% vs 6.2%, χ² = 6.020, P = .014; MDD, 12.7% vs 6.6%, χ² = 13.295, P < .001). No statistically significant difference was found in hypothyroidism rate between the early- and late-onset SZ patients (9.2% vs 10.1%, χ² = 0.234, P = .628).

Patients with early-onset affective disorder were 2.097 times (95% CI, 1.409-3.123) more likely to have hypothyroidism vs those with late-onset affective disorder (adjusted odds ratio [OR], 1.965; 95% CI, 1.198-3.221 in BD; and adjusted OR, 2.831; 95% CI, 1.378-5.817 in MDD, respectively), after adjustment for age, sex, disease duration, and mood episode (for BD).

Study limitations include the cross-sectional design, as the investigators were unable to determine a causality between early-onset affective disorders and hypothyroidism. Additionally, even though patients had not used psychiatric drugs in the months before the study, the researchers could not entirely exclude the irreversible thyroid effect of drugs. Researchers did not obtain clinical assessments of disease severity;  the study involved patients requiring hospitalization and may not have represented those with milder disease who could were be treated as outpatients.

“Longitudinal cohort studies are necessary to explore the clinical significance and potential mechanism of the association between early-onset affective disorders and hypothyroidism,” stated the researchers.

Reference

Zhao Y, Wang N, Chen J, et al. Association between early-onset affective disorders and hypothyroidism in a larger number of psychiatric drug-free patients. J Affect Disord. 2021;299:31-36. doi:10.1016/j.jad.2021.11.061