Subclinical Hypothyroidism Is Associated With Increased Risk for All-Cause and Cardiovascular Mortality in Adults

Study Questions:

Is subclinical hypothyroidism associated with increased risk for mortality?

Methods:

Subjects with no history of thyroid disease at baseline were followed over a 10-year period. Data on this cohort were collected through four private Taiwanese Health Screening Centers from 1998 to 1999. All participants were 20 years or older. Subclinical hypothyroidism was defined as a serum thyroid-stimulating hormone (TSH) level of 5.0-19.96 mIU/L with normal total thyroxine concentrations. Euthyroidism was defined as a serum TSH level of 0.47 to 4.9 mIU/L.

Results:

A total of 115,746 participants were included in this study, of which 1,841 had subclinical hypothyroidism and 113,905 were euthyroid. Participants with subclinical hypothyroidism were more likely to be older, female, and have higher body mass index. Risk factors such as diabetes, hyperlipidemia, and hypertension were also more prevalent among participants with subclinical hypothyroidism. During the follow-up, 3,669 deaths occurred, of which 680 were due to cardiovascular disease (CVD). Compared to subjects with euthyroidism, subjects with subclinical hypothyroidism were at increased risk for all-cause mortality (relative risk [RR], 1.30; 95% confidence interval [CI], 1.02-1.66) and CVD mortality (RR, 1.68; 95% CI, 1.02-2.76), after adjustment for age, sex, body mass index, diabetes, hypertension, dyslipidemia, smoking, alcohol consumption, betel nut chewing, physical activity, income, and education level.

Conclusions:

The investigators concluded that adult Taiwanese patients with subclinical hypothyroidism have an increased risk for all-cause mortality and CVD death compared to adults who are euthyroid.

Perspective:

Most clinicians understand the associations between hypothyroidism and CVD risk factors. However, these findings suggest that subclinical hypothyroidism may be a concern as well. These findings need to be replicated in other cohorts, and if consistent, the question of treating subclinical hypothyroidism to reduce CVD risk remains to be answered.

Clinical Topics: Dyslipidemia, Prevention, Hypertension

Keywords: Thyrotropin, Hyperlipidemias, Thyroxine, Hypothyroidism, Hypertension


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