Abstract Body (Do not enter title and authors here): Background:
Patients with ischemic heart disease and hypothyroidism face a higher risk of death compared to euthyroid individuals in the U.S. The relationship between Hypothyroidism and ischemic heart disease is notable, as hypothyroidism can exacerbate cardiovascular conditions and increase the risk of ischemic heart disease.

Objective:
Aim of our study is to evaluate trends and disparities in hypothyroidism and ischemic heart disease mortality among US adults from 1999 to 2020.

Methods:
Mortality data from CDC WONDER database were analyzed for the period 1999 to 2020 to examine hypothyroidism and ischemic heart disease mortality among U.S. adults aged more than 25 years with ICD-10 codes E03.9 for hypothyroidism and I20-I25 for Ischemic Heart Diseases. We calculated age-adjusted mortality rates (AAMRs) per 100,000 individuals stratified by year, sex, race/ethnicity, urbanization, states and geographic region. Joinpoint regression analysis was performed to calculate annual percent changes (APCs) with 95% confidence intervals (CIs) and p-value<0.01


Results:
Between 1999 and 2020, there were a total of 133,413 deaths related to hypothyroidism and ischemic heart disease. AAMR decreased from 3.56 in 1999 to 2.33 in 2018 and then increased to 2.78 in 2020 (2018-2020 APC 11.69 [95% CI, 2.14 to 22.12]). Females had higher AAMR (3.08) compared to males (2.3), and both sexes experienced an initial decline in AAMRs (1999-2018 APC: -3.20 [F], -1.12 [M]) followed by a rise from 2018 to 2020 (APC: 11.28 [F], 11.69 [M]). Among the races in descending order, AAMR was highest in non-Hispanic white individuals(2.94) followed by Hispanics (1.91), Black individuals(1.56) and lastly Asians (1.09). AAMRs in Non metro areas were higher (3.56) than in the Metro areas (2.61). Among census regions, AAMR was highest in the Midwest (3.27) followed by Northeast (2.89), West (2.55) and lastly South (2.51). West Virginia (5.97) and North Dakota (5.69) shows highest AAMRs while, Utah (1.01) and Nevada (1.13) shows the lowest AAMRs.

Conclusion:
From 1999 to 2018, the Age-Adjusted Mortality Rates (AAMRs) for hypothyroidism and ischemic heart disease in the U.S. generally decreased. However, after 2018, there was a dramatic increase in AAMRs across nearly all demographic groups including sex, race and geographic regions. This rise calls for further investigation and highlights the need for improved access to care, earlier diagnosis, and protective measures for vulnerable populations.