How much does hypothyroidism raise your risk of heart disease?
The evidence is strong and consistent: having hypothyroidism significantly increases your risk of developing and dying from heart disease. A large genetic study using data from over 500,000 people found that hypothyroidism causes a 7.8% increase in the risk of coronary heart disease [2]. Another study found that people with subclinical hypothyroidism (a mild form where TSH is high but thyroid hormones are still normal) had a 90% higher risk of dying from any cause during follow-up, and heart disease explained about 14% of that increased risk [6]. This means the link is not just an association—it appears to be causal.
The risk is even more pronounced in certain groups. For example, a study of patients with ischemic heart disease (a type of heart disease caused by narrowed arteries) found that 16.7% had undiagnosed subclinical hypothyroidism and 7.8% had overt hypothyroidism [5]. In children with congenital heart disease, TSH levels were significantly higher and non-autoimmune hypothyroidism was more common than in healthy children [9]. Even maternal hypothyroidism during pregnancy increases the child's risk of developing cardiovascular disease later in life by 23%, and the risk is highest when the mother's hypothyroidism occurs during pregnancy itself (71% higher risk) [3].
How does an underactive thyroid damage your heart?
Hypothyroidism harms the heart through several well-understood mechanisms. The most direct is through cholesterol: hypothyroidism causes your liver to clear LDL ("bad") cholesterol more slowly, leading to higher levels in your blood. One study showed that hypothyroidism lowers HDL ("good") cholesterol and apolipoprotein A-I, both of which protect against heart disease [2]. Another study found that 95.5% of hypothyroid patients with heart disease had dyslipidemia (abnormal cholesterol levels) [5]. Women with subclinical hypothyroidism had significantly higher triglycerides, VLDL (a type of fat), and a higher atherogenic index of plasma (a measure of heart disease risk) compared to women with normal thyroid function [8].
Beyond cholesterol, hypothyroidism directly affects the heart muscle and blood vessels. A study of patients who developed hypothyroidism while taking the heart medication amiodarone found that their heart muscle mass increased by 30.2% and their heart's pumping ability decreased by 22.7% [7]. Hypothyroidism also raises blood pressure: one study found that hypothyroid patients with heart disease had significantly higher systolic and diastolic blood pressure [5]. Additionally, hypothyroidism is linked to higher blood sugar levels (HbA1c), which further increases heart disease risk [5][11]. One study found that HbA1c (a measure of average blood sugar over 3 months) explained about 7.3% of the effect of hypothyroidism on coronary heart disease [11].
The thyroid hormone also plays a critical role in the heart's electrical system. In heart transplant patients, low thyroid hormone levels after surgery were linked to worse survival, and giving thyroid hormone replacement improved outcomes [1]. Another study found that patients with Parkinson's disease or dementia with Lewy bodies (conditions where abnormal protein deposits affect the heart's nerves) had a much higher rate of sudden cardiac death (51.3%) compared to controls (22.6%), suggesting that thyroid-related nerve damage can trigger fatal heart rhythms [10].
What does this mean for you? Should you be screened or treated?
If you have hypothyroidism—or even if you just have symptoms like fatigue, weight gain, or feeling cold—you should talk to your doctor about your heart disease risk. The evidence strongly suggests that treating hypothyroidism with thyroid hormone replacement (levothyroxine) can reduce that risk. For example, in heart transplant patients, giving levothyroxine to the donor or recipient was associated with better survival at 30 days, 1 year, and 2 years [1]. Current guidelines recommend treating subclinical hypothyroidism when TSH is above 10 mIU/L, especially in younger people, though the benefit is less clear for those over 65 [12].
Screening is particularly important if you have other risk factors. One study found that the strongest predictor of hypothyroidism in heart disease patients was a high body mass index (BMI), with an odds ratio of 7.9—meaning obese patients were nearly 8 times more likely to have undiagnosed hypothyroidism [5]. Other risk factors include being female, having high blood pressure, and having poorly controlled diabetes (HbA1c ≥ 10%) [5]. If you take the heart medication amiodarone, you are at especially high risk: a meta-analysis found that 23.4% of heart patients on amiodarone develop hypothyroidism [4], and this can worsen heart function [7].
The bottom line: hypothyroidism is a treatable cause of heart disease. If you have an underactive thyroid, getting your thyroid levels to a healthy range (a middle-normal TSH, around 1.2-1.95 mIU/L) may lower your cholesterol, blood pressure, and heart disease risk [6]. Even if you don't have symptoms, if you have heart disease or risk factors like high cholesterol or obesity, a simple blood test for TSH could uncover a hidden contributor to your heart problems.
About These Sources
This answer is built on 12 peer-reviewed studies — published from 2020 to 2025, 6 from 2024 or later, 3 in Q1 journals, collectively cited 63 times — selected as the most relevant from 14 studies that passed quality screening, drawn from 62 papers retrieved from a database of over 500 million.
Sources used in this answer
The Perioperative Period of Heart Transplantation Is Affected by Thyroid Hormone Status
In a prospective study of 283 heart transplant patients, lower thyroid hormone levels after surgery were linked to worse outcomes, and giving levothyroxine to donors or recipients improved survival at 30 days, 1 year, and 2 years.
From Hypothyroidism to Coronary Heart Disease: Unraveling the Lipid Profile Link: A Mendelian Randomization Study
Using Mendelian randomization in over 500,000 people, this study found that hypothyroidism causally increases coronary heart disease risk by 7.8%, partly by lowering HDL cholesterol and apolipoprotein A-I.
Association of Maternal Hypothyroidism With Cardiovascular Diseases in the Offspring
In a nationwide Danish cohort of over 1 million births, children of mothers with hypothyroidism had a 23% higher risk of developing cardiovascular disease, with the highest risk (71% increase) when hypothyroidism occurred during pregnancy.
Prevalence of Amiodarone Induced Hypothyroidism and Hyperthyroidism in Patients with Heart Diseases: A Systematic Review and Meta-Analysis.
A meta-analysis found that among heart disease patients taking amiodarone, the pooled prevalence of hypothyroidism was 23.4% and hyperthyroidism was 11.6%, highlighting the need for thyroid monitoring.
Risk factors of ischemic heart disease among hypothyroid patients in Bangladesh
In a cross-sectional study of 90 patients with ischemic heart disease in Bangladesh, 16.7% had subclinical and 7.8% had overt hypothyroidism; strongest predictors were female sex, obesity (BMI odds ratio 7.9), high blood pressure, and poor diabetes control.
Association of Subclinical Hypothyroidism and Cardiovascular Disease With Mortality.
In a US national cohort of 9,020 adults, subclinical hypothyroidism was associated with a 90% higher risk of all-cause mortality, with cardiovascular disease mediating 14.3% of that effect.
Features of clinical manifestations of coronary heart disease in patients with amiodarone-associated hypothyroidism
Among 810 coronary heart disease patients taking amiodarone, 3.4% developed hypothyroidism, which led to a 30.2% increase in left ventricular mass and a 22.7% decrease in myocardial contractility.
Assessment of Cardiovascular Disease Risk in Females with Subclinical Hypothyroidism
In a cross-sectional study of 100 Nepalese women with subclinical hypothyroidism, they had significantly higher triglycerides, VLDL, and atherogenic index of plasma compared to 100 euthyroid controls, indicating higher cardiovascular risk.
Frequency of seropositive celiac disease and hypothyroidism among children and adolescents with congenital heart disease: A case-control study.
In a case-control study of 98 children with congenital heart disease, TSH levels and non-autoimmune hypothyroidism were significantly higher than in 100 healthy controls.
Sudden cardiac death in synucleinopathies
In a neuropathological study, 51.3% of patients with α-synucleinopathies (e.g., Parkinson's disease) died from sudden cardiac death, compared to 22.6% of controls, suggesting thyroid-related nerve damage can trigger fatal arrhythmias.
The role of glycemic traits in the mediation of the causal effect of hypothyroidism on coronary heart disease.
Using Mendelian randomization, this study found that hypothyroidism causally increases coronary heart disease risk (odds ratio 2.75), with HbA1c mediating 7.3% of that effect.
Hypothyroidism and metabolic cardiovascular disease
This review summarizes that both overt and subclinical hypothyroidism increase cardiovascular risk through effects on blood pressure, endothelial function, and lipids, and recommends treating subclinical hypothyroidism when TSH >10 mIU/L, especially in younger people.