Hashimoto's and fatty liver disease are two increasingly common conditions that often coexist, affecting millions of people in the UK. Hashimoto's thyroiditis, an autoimmune disorder causing underactive thyroid, and non-alcoholic fatty liver disease (NAFLD), characterised by excess liver fat, share overlapping risk factors including obesity, insulin resistance, and metabolic syndrome. The thyroid gland regulates metabolism and influences how the liver processes fats, whilst the liver converts thyroid hormones into their active form. Understanding the connection between these conditions is essential for effective management, as optimising thyroid function and addressing metabolic health can benefit both organs and improve overall wellbeing.
Summary: Hashimoto's thyroiditis and fatty liver disease frequently coexist due to shared metabolic risk factors, though no direct causation is established.
- Hashimoto's is an autoimmune condition causing hypothyroidism, whilst NAFLD involves excess liver fat accumulation in people who drink little or no alcohol.
- Both conditions share risk factors including obesity, insulin resistance, type 2 diabetes, and metabolic syndrome.
- Hypothyroidism slows metabolism and alters lipid processing, potentially increasing hepatic fat accumulation.
- Diagnosis involves thyroid function tests (TSH, FT4, TPO antibodies) for Hashimoto's and liver function tests, imaging, and fibrosis scoring (FIB-4, ELF) for NAFLD.
- Treatment includes levothyroxine for hypothyroidism and lifestyle modifications (weight loss, diet, exercise) for NAFLD, as no licensed pharmacological therapy exists for fatty liver.
- Patients with an ELF score of 10.51 or above indicating advanced fibrosis require specialist hepatology referral.
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Understanding Hashimoto's Thyroiditis and Fatty Liver Disease
Hashimoto's thyroiditis is an autoimmune condition in which the immune system mistakenly attacks the thyroid gland, leading to chronic inflammation and progressive damage. This condition is the most common cause of hypothyroidism (underactive thyroid) in the UK, affecting approximately 1–2% of the population, with women being significantly more affected than men. The thyroid gland produces hormones that regulate metabolism, energy production, and numerous bodily functions. When Hashimoto's develops, the gradual destruction of thyroid tissue results in reduced hormone production, causing symptoms such as fatigue, weight gain, cold intolerance, and cognitive difficulties.
Non-alcoholic fatty liver disease (NAFLD) is characterised by excessive fat accumulation in the liver (hepatic steatosis) in individuals who consume little to no alcohol. To diagnose NAFLD, other causes of liver disease—including viral hepatitis, alcohol-related liver disease, haemochromatosis, autoimmune hepatitis, and drug-induced liver injury—must be excluded. In the UK, alcohol consumption below levels associated with alcohol-related liver disease (typically less than 14 units per week for women and 21 units per week for men, though NICE NG49 advises clinicians to assess alcohol intake carefully) is used as a threshold. NAFLD has become increasingly prevalent in the UK, affecting an estimated 20–30% of the general population. The condition exists on a spectrum, ranging from simple steatosis (fat accumulation without significant inflammation) to non-alcoholic steatohepatitis (NASH), which involves inflammation and liver cell damage that can progress to fibrosis, cirrhosis, and liver failure.
Both conditions share common risk factors, including obesity, insulin resistance, metabolic syndrome, and type 2 diabetes. The relationship between thyroid function and liver health is complex and bidirectional. The liver plays a crucial role in thyroid hormone metabolism, converting the inactive hormone thyroxine (T4) to the active form triiodothyronine (T3). Conversely, thyroid hormones influence hepatic lipid metabolism, cholesterol synthesis, and glucose regulation. Understanding how these two conditions may coexist and influence one another is essential for comprehensive patient management and optimal health outcomes. Further information is available from the NHS pages on underactive thyroid (hypothyroidism) and non-alcoholic fatty liver disease, and from NICE guideline NG145 (Thyroid disease: assessment and management) and NICE guideline NG49 (Non-alcoholic fatty liver disease: assessment and management).
The Link Between Hashimoto's and Fatty Liver
Research has identified an association between Hashimoto's thyroiditis and the development of non-alcoholic fatty liver disease, though it is important to note that there is no established direct causation. Several mechanisms may explain this relationship. Hypothyroidism resulting from Hashimoto's leads to a reduced metabolic rate, which can promote weight gain and alter lipid metabolism. Thyroid hormones normally stimulate lipolysis (fat breakdown) and enhance hepatic lipid clearance. When thyroid function is impaired, these processes slow down, potentially leading to increased hepatic fat accumulation.
Insulin resistance appears to be a key connecting factor between the two conditions. Observational studies have demonstrated that hypothyroidism can worsen insulin sensitivity, creating a metabolic environment conducive to both conditions. Additionally, the chronic low-grade inflammation characteristic of autoimmune thyroid disease may contribute to systemic metabolic dysfunction, potentially affecting liver health. Some emerging research suggests that thyroid autoantibodies themselves might play a role in metabolic disturbances beyond their effects on the thyroid gland, though this evidence remains limited and exploratory.
The prevalence of NAFLD appears to be higher in individuals with hypothyroidism compared to the general population, with some studies reporting rates of 30–55% in those with thyroid dysfunction, though these figures require robust confirmation and may be influenced by confounding factors such as obesity and insulin resistance. Subclinical hypothyroidism (elevated TSH with normal thyroid hormone levels) has also been associated with increased NAFLD risk in some observational studies, suggesting that even mild thyroid dysfunction may impact liver health. However, the relationship is complex and likely influenced by multiple factors including body mass index (BMI), age, gender, and genetic predisposition. It is important to note that correcting hypothyroidism with levothyroxine does not reliably reverse NAFLD; management should prioritise metabolic risk reduction through lifestyle measures and weight loss.
It is worth noting that the association may be bidirectional. Severe liver disease can affect thyroid hormone metabolism and binding protein production, potentially influencing thyroid function tests. This highlights the importance of comprehensive assessment when either condition is diagnosed, particularly in patients with multiple metabolic risk factors. Systematic reviews and meta-analyses (such as those by Mantovani et al. and He et al.) provide further context on the association between thyroid dysfunction and NAFLD.
Symptoms and Diagnosis of Both Conditions
Hashimoto's thyroiditis often develops gradually, and many patients remain asymptomatic in the early stages. Common symptoms include persistent fatigue, unexplained weight gain despite normal eating habits, sensitivity to cold, dry skin, hair loss or thinning, constipation, muscle weakness, joint pain, depression, and cognitive difficulties such as poor concentration or memory problems. Some patients may notice swelling in the neck (goitre) as the thyroid gland enlarges in response to autoimmune attack. Women may experience menstrual irregularities or fertility problems.
Diagnosis of Hashimoto's involves blood tests measuring thyroid-stimulating hormone (TSH) and free thyroxine (FT4). Primary hypothyroidism is diagnosed when TSH is elevated and FT4 is low or low-normal. To support an autoimmune aetiology, thyroid peroxidase antibodies (TPO) are measured; NICE guideline NG145 advises against routine testing of thyroglobulin antibodies (TG). Positive TPO antibodies confirm Hashimoto's thyroiditis as the cause of hypothyroidism, though antibodies are not required to diagnose or treat hypothyroidism itself. NICE guidelines recommend thyroid function testing in patients presenting with suggestive symptoms or those with other autoimmune conditions, type 1 diabetes, or a family history of thyroid disease.
Non-alcoholic fatty liver disease is often asymptomatic, particularly in early stages, and is frequently discovered incidentally during imaging performed for other reasons. When symptoms do occur, they may include fatigue, vague right upper quadrant discomfort, or hepatomegaly (enlarged liver) detected on examination. Advanced disease with fibrosis or cirrhosis may present with jaundice, ascites, or signs of portal hypertension.
Diagnosis typically begins with liver function tests (LFTs), which may show elevated alanine aminotransferase (ALT) and aspartate aminotransferase (AST), though normal LFTs do not exclude NAFLD. It is essential to exclude other causes of liver disease (viral hepatitis, alcohol-related liver disease, haemochromatosis, autoimmune hepatitis, drug-induced liver injury) and to quantify alcohol intake carefully. Ultrasound scanning is commonly used as a first-line imaging modality to detect hepatic steatosis. NICE guideline NG49 recommends a structured approach to assess fibrosis risk: first, calculate an age-adjusted FIB-4 score (low risk if <1.3 in adults under 65 years or <2.0 in adults 65 years and older; high risk if >2.67) or NAFLD fibrosis score. If the FIB-4 or NAFLD fibrosis score suggests possible advanced fibrosis, confirm with the Enhanced Liver Fibrosis (ELF) blood test. An ELF score of 10.51 or above indicates advanced fibrosis and warrants referral to a hepatology specialist. More advanced assessment may include FibroScan (transient elastography) to evaluate liver stiffness and fat content, or in some cases, liver biopsy to determine the degree of inflammation and fibrosis. When both conditions are suspected, comprehensive metabolic screening including fasting glucose or HbA1c, lipid profile, and assessment for metabolic syndrome components is essential. Further guidance is available from NICE NG145, NICE NG49, and the British Society of Gastroenterology guideline on the management of abnormal liver blood tests.
Treatment Options for Hashimoto's and Fatty Liver
Management of Hashimoto's thyroiditis centres on thyroid hormone replacement therapy when hypothyroidism develops. Levothyroxine, a synthetic form of thyroxine (T4), is the standard treatment recommended by NICE and the British Thyroid Association. The typical starting dose for adults under 65 years without cardiac disease is 1.6 micrograms per kilogram of body weight daily, with lower starting doses (25–50 micrograms daily) recommended for older patients or those with cardiovascular disease. Treatment aims to normalise TSH levels, typically targeting a TSH within the local laboratory reference range, though individual targets may vary (for example, in pregnancy, closer monitoring and lower TSH targets are required—refer to NICE NG145 for specific guidance).
Dose adjustments are made based on thyroid function tests performed 6–8 weeks after initiation or dose changes, then every 6–12 months once stable. Levothyroxine should be taken on an empty stomach, ideally 30–60 minutes before breakfast, and at a consistent time each day. Important interactions: separate levothyroxine from calcium supplements, iron supplements, and antacids by at least 4 hours, as these can interfere with absorption. Food, soya products, and high-fibre foods should also be taken several hours apart from levothyroxine. Patients should be advised that symptom improvement may take several weeks to months. Important safety considerations include avoiding overtreatment, which can cause hyperthyroid symptoms, bone loss, and atrial fibrillation, particularly in older adults. Detailed prescribing information is available in the MHRA/EMC Summary of Product Characteristics (SmPC) for levothyroxine tablets. If you experience suspected side effects from levothyroxine, report them to the MHRA Yellow Card Scheme at yellowcard.mhra.gov.uk or via the Yellow Card app.
Treatment of NAFLD currently focuses on addressing underlying metabolic risk factors, as there are no licensed pharmacological therapies specifically for NAFLD in the UK. Weight loss is the cornerstone of management, with evidence showing that losing 7–10% of body weight can significantly reduce liver fat and improve inflammation. For patients with type 2 diabetes and NAFLD, certain medications may offer additional hepatic benefits, though these are used off-label for NAFLD and should be initiated and monitored by specialists. Pioglitazone has demonstrated improvements in liver histology in some patients with NASH, but carries risks including weight gain and heart failure exacerbation. GLP-1 receptor agonists and SGLT2 inhibitors show promise in reducing liver fat content in observational studies, but robust trial evidence for NAFLD-specific outcomes is still emerging. Statins are safe and recommended for cardiovascular risk reduction in patients with NAFLD when indicated by lipid levels and cardiovascular risk assessment; they do not worsen liver disease.
Patients with advanced fibrosis or cirrhosis require specialist hepatology input and may need surveillance for hepatocellular carcinoma and varices. Referral to secondary care is recommended for patients with an ELF score of 10.51 or above (indicating advanced fibrosis), evidence of decompensated liver disease (jaundice, ascites, variceal bleeding, hepatic encephalopathy), or diagnostic uncertainty. When managing patients with both Hashimoto's and NAFLD, optimising thyroid hormone replacement is important, as adequate thyroid function may support metabolic improvements that benefit liver health. Regular monitoring of both conditions ensures treatment effectiveness and early detection of disease progression. Further guidance is available from NICE NG145, NICE NG49, and the British Society of Gastroenterology.
Lifestyle Changes to Support Thyroid and Liver Health
Dietary modifications play a crucial role in managing both Hashimoto's thyroiditis and fatty liver disease. For liver health, adopting a Mediterranean-style diet rich in vegetables, fruits, whole grains, legumes, nuts, and olive oil has demonstrated benefits in reducing hepatic fat content. Patients should limit refined carbohydrates, added sugars, and saturated fats, whilst avoiding excessive fructose consumption from sugary drinks and processed foods. Adequate protein intake supports liver repair and metabolic function. For thyroid health, ensuring sufficient intake of key nutrients is important: iodine (found in dairy products, fish, and eggs—note that most salt in the UK is not iodised), selenium (Brazil nuts, fish, eggs), and zinc (meat, shellfish, legumes) all support thyroid hormone production and metabolism.
However, patients should be cautious about iodine and selenium supplementation. Excessive iodine intake, particularly from kelp or iodine supplements, can paradoxically worsen autoimmune thyroid disease and should be avoided unless clinically indicated. Selenium supplementation can lead to toxicity if safe upper limits are exceeded; discuss any supplements with your GP or a registered dietitian before starting. Certain foods may interfere with levothyroxine absorption, including high-fibre foods, soya products, calcium supplements, and iron supplements, so these should be consumed at least 4 hours apart from thyroid medication. Patients should discuss any dietary supplements with their GP, as some may interact with thyroid medication or affect liver function. Further advice is available from the British Dietetic Association factsheets on iodine and selenium.
Regular physical activity benefits both conditions significantly. The UK Chief Medical Officers recommend at least 150 minutes of moderate-intensity aerobic activity weekly, combined with resistance training on two or more days. Exercise improves insulin sensitivity, promotes weight loss, reduces hepatic fat accumulation, and supports overall metabolic health. For patients with hypothyroidism experiencing fatigue, starting with gentle activities such as walking and gradually increasing intensity as energy levels improve is advisable.
Weight management is particularly important when both conditions coexist. Even modest weight loss of 5–10% can improve liver enzymes, reduce hepatic steatosis, and may improve insulin sensitivity. Patients should aim for gradual, sustainable weight loss of 0.5–1 kg per week through combined dietary changes and increased physical activity. Alcohol consumption should be limited in line with UK Chief Medical Officers' low-risk drinking guidelines: no more than 14 units per week, spread over 3 or more days, with several alcohol-free days each week. In patients with NAFLD, consider abstaining from alcohol or keeping intake very low. In those with advanced fibrosis or cirrhosis, alcohol should be avoided entirely.
Additional lifestyle measures include stress management, as chronic stress can affect both thyroid function and metabolic health. Adequate sleep (7–9 hours nightly) supports hormonal balance and metabolic regulation. Patients should attend regular monitoring appointments: for stable hypothyroidism, thyroid function tests are typically performed every 6–12 months. For NAFLD, NICE NG49 recommends periodic reassessment of fibrosis risk (for example, repeating age-adjusted FIB-4 or NAFLD fibrosis score every 3 years in adults), with liver function tests performed as clinically indicated. When to contact your GP: seek medical advice if experiencing new or worsening symptoms such as significant fatigue, unexplained weight changes, abdominal pain or swelling, jaundice (yellowing of skin or eyes), dark urine, pale stools, or signs of fluid retention. Patients should also report any side effects from levothyroxine or concerns about medication effectiveness. With appropriate medical management and committed lifestyle modifications, most patients with both conditions can achieve good symptom control and reduce their risk of disease progression.
Frequently Asked Questions
Can Hashimoto's thyroiditis cause fatty liver disease?
Hashimoto's does not directly cause fatty liver disease, but the two conditions frequently coexist due to shared metabolic risk factors. Hypothyroidism from Hashimoto's slows metabolism and alters how the liver processes fats, which may contribute to fat accumulation in the liver alongside other factors like obesity and insulin resistance.
Will treating my underactive thyroid improve my fatty liver?
Optimising thyroid hormone levels with levothyroxine may support metabolic improvements, but it does not reliably reverse fatty liver disease on its own. The most effective treatment for NAFLD remains weight loss of 7–10% of body weight through diet and exercise, alongside management of metabolic risk factors like diabetes and high cholesterol.
What are the warning signs that my Hashimoto's and fatty liver are getting worse?
Contact your GP if you experience worsening fatigue, unexplained weight changes, abdominal pain or swelling, jaundice (yellowing of skin or eyes), dark urine, pale stools, or fluid retention. These symptoms may indicate progression of either condition and require prompt medical assessment and possible adjustment of your treatment plan.
Can I take levothyroxine if I have liver problems?
Yes, levothyroxine is safe to take with fatty liver disease and does not worsen liver function. The liver plays a role in converting thyroid hormones, so maintaining adequate thyroid replacement is important for overall metabolic health, though severe liver disease may affect thyroid hormone metabolism and require specialist monitoring.
How do I know if my fatty liver has progressed to advanced fibrosis?
Your GP will calculate a FIB-4 score using your age, liver enzymes, and platelet count; if this suggests possible advanced fibrosis, you will have an Enhanced Liver Fibrosis (ELF) blood test. An ELF score of 10.51 or above indicates advanced fibrosis and requires referral to a hepatology specialist for further assessment and management.
What diet changes help both Hashimoto's and fatty liver at the same time?
A Mediterranean-style diet rich in vegetables, fruits, whole grains, legumes, and olive oil benefits both conditions by reducing liver fat and supporting metabolic health. Ensure adequate iodine, selenium, and zinc from food sources, limit refined carbohydrates and added sugars, and take levothyroxine at least 4 hours apart from high-fibre foods, soya, calcium, and iron supplements to avoid absorption issues.
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