ALT (Alanine Aminotransferase)
| Clinical | Optimal | |
|---|---|---|
| Male | 0 - 50 U/L | Below 41 U/L (optimal below 25 U/L) |
| Female | 0 - 35 U/L | Below 33 U/L (optimal below 20 U/L) |
What is ALT (Alanine Aminotransferase)?
Alanine aminotransferase (ALT) is an enzyme found predominantly in your liver cells. When liver cells are healthy and intact, ALT remains inside the cells carrying out its normal function of helping to metabolise amino acids. However, when liver cells are damaged or inflamed, ALT leaks out into the bloodstream, causing your blood levels to rise.
ALT is considered the most liver-specific of the commonly tested liver enzymes. While it is found in small amounts in other tissues, elevated ALT in your blood almost always points to something happening in your liver. This makes it an invaluable early warning marker for liver damage.
In the UK, liver disease has become increasingly prevalent, driven largely by rising rates of non-alcoholic fatty liver disease (NAFLD), which now affects approximately one in three adults. Regular ALT monitoring is a simple yet powerful way to track your liver health and catch problems early when they are most reversible.
Why ALT (Alanine Aminotransferase) Matters for Your Health
Your liver performs over 500 essential functions, including detoxification, protein synthesis, bile production, and metabolising nutrients, medications, and hormones. Even mild liver damage, if sustained over time, can progress to serious conditions including fibrosis, cirrhosis, and liver cancer.
For longevity, liver health is paramount. The liver is one of your body's most remarkable organs, with an extraordinary capacity to regenerate and heal itself, but only if damage is caught early and its cause addressed. Persistently elevated ALT, even mildly so, is associated with increased all-cause mortality and cardiovascular risk.
ALT is particularly important in the context of metabolic health. Non-alcoholic fatty liver disease is now the most common cause of elevated ALT in the UK and is strongly linked to insulin resistance, obesity, and metabolic syndrome. Monitoring ALT alongside your metabolic markers provides a comprehensive picture of your metabolic health.
ALT (Alanine Aminotransferase)& Your Wearable Data
Alanine aminotransferase (ALT) is the most liver-specific enzyme in routine blood panels. While wearable devices do not directly measure liver function, activity data provides useful context. Regular moderate exercise is associated with lower ALT levels, as physical activity helps reduce liver fat (hepatic steatosis). Your wearable's weekly active minutes and calorie expenditure data correlate with improved liver enzyme profiles over time.
Intense exercise can transiently elevate ALT. If your wearable data shows a particularly strenuous training session 24-48 hours before your blood draw, this may explain a mildly elevated result. Heavy resistance training and endurance events are common causes of exercise-induced ALT elevation that is benign and temporary.
Sleep and stress patterns tracked by your wearable are also relevant. Chronic sleep deprivation and sustained stress (reflected in persistently low HRV) are associated with non-alcoholic fatty liver disease and elevated liver enzymes. Improving sleep consistency and stress recovery as tracked by your wearable may support healthier ALT levels.
What High ALT (Alanine Aminotransferase) May Suggest
Elevated ALT indicates that liver cells are being damaged and releasing this enzyme into your bloodstream. The most common cause in the UK today is non-alcoholic fatty liver disease (NAFLD), which occurs when excess fat accumulates in the liver, typically driven by insulin resistance, obesity, and a diet high in sugar and refined carbohydrates.
Other common causes include excessive alcohol consumption, viral hepatitis (hepatitis B and C), certain medications (including paracetamol at high doses), autoimmune liver disease, and coeliac disease. Intense exercise can cause a temporary, benign rise in ALT levels.
Mildly elevated ALT (less than three times the upper limit) often reflects early, reversible liver damage. However, it is important to note that ALT can be normal even in the presence of significant liver disease, particularly in advanced fibrosis where fewer healthy liver cells remain. If your results suggest elevated ALT, identifying and addressing the underlying cause is crucial for preventing progression.
What Low ALT (Alanine Aminotransferase) May Suggest
Low ALT levels are generally normal and indicate that your liver cells are healthy and intact. There is no well-established clinical concern with low ALT levels in healthy individuals.
However, some research has suggested that very low ALT (below 10 U/L) in older adults may be associated with frailty, sarcopenia (muscle loss), or overall poor nutritional status, as ALT is also present in muscle tissue. This finding is more relevant to elderly or unwell populations.
For most people, a low ALT is a reassuring finding that suggests good liver health.
How to Optimise Your ALT (Alanine Aminotransferase)
Food
Reduce added sugars and fructose, particularly from sugary drinks and processed foods, as excess fructose is a primary driver of fatty liver, Increase intake of cruciferous vegetables like broccoli, Brussels sprouts, and kale, which support liver detoxification pathways, Include foods rich in antioxidants such as berries, green tea, and turmeric, which help protect liver cells from oxidative damage, Consume adequate protein from lean sources to support liver repair and regeneration, Add garlic and onions, which contain sulphur compounds that support liver glutathione production
Lifestyle
Reduce or eliminate alcohol consumption, as alcohol is directly toxic to liver cells and is one of the most modifiable risk factors, Lose excess weight gradually, as even 5-10% weight loss can dramatically reduce liver fat and lower ALT levels, Exercise regularly, combining aerobic activity and resistance training, both of which independently reduce liver fat, Review medications with your GP, as some over-the-counter medications, including paracetamol, can elevate ALT with regular use
Supplements
Milk thistle (silymarin, 200-400mg daily) has a long history of use for liver support and some evidence for reducing ALT in fatty liver disease, N-acetyl cysteine (NAC, 600-1200mg daily) supports glutathione production, the liver's primary antioxidant, Omega-3 fish oil (2-4g daily) may help reduce liver fat and lower elevated ALT levels
When to Speak to Your GP
See your GP if your ALT results suggest levels more than twice the upper limit of normal, or if even mildly elevated ALT persists across multiple tests. Seek urgent medical advice if ALT exceeds five times the upper limit, as this may indicate significant acute liver injury. Also consult your GP if elevated ALT is accompanied by symptoms such as yellowing of the skin or eyes, dark urine, abdominal pain, or persistent fatigue.
References
- NHS. Liver function tests — Overview. nhs.uk
- NICE. Non-alcoholic fatty liver disease (NAFLD): assessment and management. NICE guideline NG49. nice.org.uk
- BMJ. Kwo PY, et al. ACG Clinical Guideline: evaluation of abnormal liver chemistries. Am J Gastroenterol. 2017;112(1):18-35. pubmed.ncbi.nlm.nih.gov
- Lancet. Newsome PN, et al. Guidelines on the management of abnormal liver blood tests. Gut. 2018;67(1):6-19. pubmed.ncbi.nlm.nih.gov
Medical Disclaimer— This content is for general educational and informational purposes only. It does not constitute medical advice, diagnosis, or treatment. Omniwo Ltd is a wellness information service and is not a medical device, clinical laboratory, or regulated healthcare provider under MHRA guidelines. The “optimal ranges” presented on this page are based on published clinical guidelines (WHO, NICE, NHS) and peer-reviewed research; they represent functional wellness targets and may differ from standard laboratory reference ranges. Individual results should always be interpreted by a qualified healthcare professional (such as your GP) who understands your full medical history. Do not start, stop, or change any medication or supplement based solely on this information. If you are experiencing symptoms, seek medical attention promptly.