Alanine aminotransferase (ALT) is commonly tested as a marker of liver health. High levels often point to liver damage or disease. Read on to find out what can cause your levels to increase.
Healthy liver cells store most of your ALT, but small amounts are also found in the muscles and blood. When liver cells are damaged due to illness, injury, or medication, they release ALT, increasing its blood levels .
Therefore, ALT blood levels are a marker of liver health: low levels typically indicate a healthy liver, while high levels suggest liver damage .
However, a result that’s higher than normal, doesn’t necessarily mean that you have a health condition that needs treatment. If your blood tests reveal you have elevated ALT levels, speak with your doctor about what the results might mean. Your doctor might recommend further testing to determine what the underlying cause of the elevated ALT is.
The normal range is around 7-35 U/L in women and 7-40 U/L in men. There may be some lab-to-lab variability in ranges due to differences in equipment, techniques, and chemicals used.
Causes listed below are commonly associated with high ALT. Work with your doctor or other health care professional for an accurate diagnosis. Your doctor will interpret your ALT result, taking into account your medical history, signs and symptoms, and other test results.
ALT levels increase in response to liver diseases, such as :
- Fatty liver or non-alcoholic fatty liver disease (NAFLD). Fatty liver affects approximately 35% of the US population and often occurs alongside diabetes and obesity .
- Viral hepatitis. Usually results in extremely high ALT levels [7, 8, 9, 10].
- Autoimmune hepatitis [11, 12]
- Liver cancer
Excessive alcohol consumption is the most common cause of liver disease in the Western Hemisphere .
In multiple studies from around the world (1.1 million Korean participants, 46k English men, 24k Americans, 6k Koreans, and 125 Italians), ALT levels increased with daily alcohol consumption [17, 18, 19, 20, 21, 22].
Alcohol breakdown takes a significant toll on liver health by causing free radical damage and increasing levels of inflammatory markers (TNF-α). Long term, excessive alcohol consumption leads to liver cell death, which releases ALT from the liver into the bloodstream [23, 24, 16].
Limited drinking may not increase ALT levels in normal-weight individuals due to its ability to improve insulin sensitivity, which seems to reduce ALT, according to trials on almost 14k people [25, 26].
There are many drugs that can increase ALT by causing liver damage, but this usually only happens in a small percentage of the people taking the drug.
But while the percentage is small, it adds up when we look at it on the population level. In fact, over-the-counter and prescription drugs are among the most common causes of elevated ALT. The same applies to natural products and supplements.
That’s why it’s important to tell your doctor about all of the drugs and/or supplements you are taking.
Drugs and supplements that can increase ALT include:
- Non-steroidal anti-inflammatory drugs (e.g. ibuprofen) [27, 28]
- Cholesterol-lowering drugs (e.g., statins) 
- Acetaminophen (Tylenol, Panadol) overdose [27, 30]
- Antibiotics 
- Opioids 
- Chemotherapy drugs 
- Vitamin A (retinoids) [32, 33]
- Kava 
- Cocaine (intoxication) 
- Methamphetamines 
ALT is often abnormal in anorexia, occurring in almost half of all people with the disorder. Weight loss and fasting can cause mild elevations in ALT (2-3x normal), while further elevations (4-30x normal) can happen in more severe cases with starvation .
Stomach fat is more dangerous than general obesity and often accompanies conditions such as diabetes and liver disease. Waist circumference and stomach fat more accurately predicted elevated ALT than the measurement of body mass index (BMI), as seen in multiple studies of over 17,000 adults, adolescents, and children [43, 44, 45, 46, 47, 48, 49, 50].
In a study of 424 patients with inflamed gallbladders (cholecystitis), those without gallstones had moderately raised ALT levels (82.5 U/L), and those with gallstones had noticeably raised ALT levels (95 U/L) .
Gallstones also cause pancreatitis by blocking the bile duct and forcing the bile back into the pancreas .
The ALT levels of patients with pancreas inflammation due to gallstones was 200 U/L on average, in a study of 543 people .
In a study with 16 patients with various muscle injuries, extreme exercise and seizures increased ALT levels .
In another study, almost 88% of 232 patients with muscular dystrophy, an inherited disease where muscles weaken and waste away, had high levels of ALT .
Underactive thyroid gland (hypothyroidism) is often associated with being overweight, fatty liver, and higher ALT levels .
ALT can also increase in health conditions that are not typically associated with the liver but can affect liver function, such as:
- Mononucleosis 
- Dengue fever [64, 65]
- HIV [66, 67]
- Celiac disease – liver injury due to untreated celiac disease is called celiac hepatitis and is usually successfully treated with a gluten-free diet 
- Hemochromatosis, a genetic disorder that causes iron to build up in cells 
There are several large population studies that have found a link between higher ALT levels and health conditions such as diabetes, heart disease, or and other metabolic issues. However, there is no proof that any of these associations are causal. It is much more likely that they are all results of underlying issues such as obesity and chronic inflammation.
In a meta-analysis of 17 studies involving over 60k participants, higher ALT levels were associated with a higher risk of type 2 diabetes. However, the association was modest, and scientists think it may not be clinically relevant (i.e. may be due to publication bias) .
In a 5-year study with 724 participants, elevated ALT levels slightly improved the prediction of future development of diabetes, in addition to other factors, such as BMI, fasting blood sugar, and family history .
Metabolic syndrome describes a number of interconnected symptoms that increase the risk of heart disease and diabetes. These include high blood pressure, high cholesterol, high blood sugar, high triglycerides, and insulin resistance .
In a meta-analysis of 5 studies with over 29k participants, the risk of developing metabolic syndrome increased by 14% for every additional 5 U/L of ALT in the blood .
In another study with over 28k people, those with the highest ALT levels were more likely to suffer from metabolic syndrome than those with the lowest levels .
According to a meta-analysis of 29 studies with 1.23 million participants, ALT levels were not associated with heart disease .
In another meta-analysis of over 1 million participants, lower ALT levels were associated with a higher risk of heart disease .
In a meta-analysis of 29 studies with 1.23 million participants, higher ALT levels were associated with a moderately increased likelihood of stroke .
In a study with 280k Asian participants, men with elevated levels of ALT were more likely to suffer a stroke than men with low ALT, though this association was less prominent in women .
In a meta-analysis of 19 studies with 9.24 million participants, Asian participants in the top third for ALT levels were 43% more likely to die from any cause than those in the bottom third. This association was not seen in North American participants .
ALT is most commonly increased in response to liver disease or liver damage, caused by alcohol, drugs, supplements, or toxins. Other causes of high ALT include obesity, anorexia, biliary disease, muscle damage and disease, heart attack, hypothyroidism, and infections and diseases that can impair liver function.
Higher ALT levels have been linked with adverse health effects such as diabetes, heart disease, stroke, and metabolic syndrome. However, these associations are likely a result of common underlying issues such as obesity and/or chronic inflammation.
This post is part of a series about ALT. Find out how to naturally lower your levels in the next part.