The Connection Between Hypothyroidism and Non-alcoholic Fatty Liver Disease

In a cross-sectional study, Korean researchers investigated the connection between the broad spectrum of hypothyroidism and non-alcoholic fatty liver disease (NAFLD). Their findings were published online in “Non-alcoholic fatty liver disease across the spectrum of hypothyroidism,”which appeared in the Journal of Hepatology.

A total of 4,648 patients were included in the study; the researchers evaluated health check-ups from these patients. The mean age of the participants was 48.6±11.8 years old, and 62.4% were female.

Healthy liver compared with fatty liver disease

Researchers divided the patients into two groups—a case group and a control group. There were 2,324 participants with hypothyroidism in the case group; and there were 2,324 participants in the control group. Patients in the control groups were age- and sex-matched to the participants in the case group.

Study participants were classified as having either subclinical thyroid-stimulating hormone (TSH) levels of greater than or equal to 4.1 mIU/L and normal free thyroxine (T4) levels between 0.7 and 1.8 ng/dL, or they were categorized as having overt hypothyroidism, with a free T4 of less than 0.7 ng/dL.

NAFLD was diagnosed in these patients by using typical ultrasonography. Another diagnostic criterion for NAFLD is alcohol consumption of less than 20 g/day and an absence of other causes of liver disease.

Researchers found that NAFLD was significantly linked to hypothyroidism (30.2% patients in the case group vs 19.5% patients in the control group; p<0.001).

Additionally, the prevalence of NAFLD and abnormal liver enzyme levels (ALT, which is defined as greater than 33/25 IU/L) progressively increased as the grade of hypothyroidism increased. For patients who had subclinical hypothyroidism, 29.9% of them had NAFLD, and for patients who had overt hypothyroidism, 36.3% of them had NAFLD (p<0.001). Also, researchers found that 20.1% of patients with subclinical hypothyroidism and 25.9% of patient with overt hypothyroidism had abnormal ALT (p<0.001).

Researchers also used multivariate regression analysis. This analysis showed that NAFLD was statistically significantly linked to hypothyroidism (odds ratio [OR]: 1.38; 95% confidence interval [CI]: 1.17 to 1.62). The analysis also showed that NAFLD was statistically significantly linked to the grade of hypothyroidism in a dose-dependent manner (OR: 1.36; 95% CI: 1.16 to 1.61 for patients with subclinical hypothyroidism and OR: 1.71; 95% CI: 1.10 to 2.66 for patients with overt hypothyroidism).

The research team determined that subclinical hypothyroidism—even in the range of upper normal TSH levels—was linked to non-alcoholic fatty liver disease in a dose-dependent manner. Furthermore, hypothyroidism is closely linked to NAFLD separate from known metabolic risk factors. These findings confirm a pertinent clinical relationship between hypothyroidism and NAFLD.

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