Low thyroid hormone status as a cardiovascular risk factor: A cross-sectional study from NHANES 2007–2012

The relationship between thyroid hormone levels and ischemic heart disease (IHD) remains controversial. This study investigates the association between serum thyroid hormones and IHD in a US population. This cross-sectional study utilized NHANES 2007–2012 data with 1864 participants. IHD was defined as self-reported physician-diagnosed coronary heart disease, angina, or myocardial infarction. Serum FT3 and TT3 levels were measured and categorized into quartiles. Four multivariable logistic regression models were constructed with progressive adjustment for demographics, socioeconomic factors, lifestyle variables, and comorbidities. Restricted cubic spline modeling assessed nonlinear dose–response relationships. Among 1864 participants, 53 (2.84%) had IHD. Participants with IHD were older (median age 69 vs 60 years, P  < .001), more likely non-Hispanic White (71.70% vs 45.17%, P  = .004), and had a higher prevalence of diabetes (47.17% vs 18.22%, P  < .001) and hypertension (81.13% vs 47.82%, P  < .001). Both FT3 and TT3 levels were lower in participants with IHD (FT3: 2.8 vs 3.05 pg/mL, P  < .001; TT3: 94 vs 110 ng/dL, P  < .001). After adjusting for confounders, higher FT3 levels were associated with reduced IHD odds (OR: 0.34, 95% CI: 0.13–0.83, P  = .027). In quartile analysis, participants in the highest FT3 quartile had 76% lower IHD odds versus the lowest quartile (OR: 0.24, 95% CI: 0.07–0.65, P for trend < .05). Higher TT3 levels showed a significant inverse association (OR: 0.98, 95% CI: 0.97–0.99 per unit increase). Participants in the highest TT3 quartile had 78% lower IHD odds versus the lowest quartile (OR: 0.22, 95% CI: 0.06–0.60, P for trend < .05). Restricted cubic spline analyses revealed nonlinear dose–response relationships for both hormones ( P for nonlinearity < .05). Our findings demonstrate significant inverse associations between serum thyroid hormone levels (FT3 and TT3) and ischemic heart disease, with nonlinear dose–response relationships. Thyroid hormone status may serve as a biomarker for cardiovascular risk assessment and a potential therapeutic target for IHD prevention.