Physiological Role
ALT (alanine aminotransferase) is an intracellular enzyme concentrated in hepatocytes, the functional cells of the liver. It catalyzes the transfer of an amino group from alanine to alpha-ketoglutarate, producing pyruvate. This reaction is essential to amino acid metabolism and gluconeogenesis (glucose production from non-carbohydrate substrates).
When hepatocyte membranes are compromised, ALT leaks into the bloodstream. Circulating levels therefore reflect the cellular integrity of the liver. Unlike AST (aspartate aminotransferase), which is present in several organs, ALT is highly specific to hepatic tissue. This specificity makes it a preferred marker for liver function assessment.
ALT is also present in skeletal muscle, though at much lower concentrations. A very low level may reflect decreased muscle mass, making it an indirect marker of sarcopenia in older adults.
Reference Ranges
Depending on the biomarker, Singular ranges are based on a synthesis of nutritional or clinical reference points and longevity research. They do not replace your laboratory's reference values or your healthcare professional's advice.
Female
Male
Biological Significance
An ALT level within the optimal range indicates that hepatocytes are functioning normally, without excessive enzyme release into the bloodstream. This is the ideal scenario for long-term liver health.
Elevated values signal increased liver stress. The most common causes include hepatic steatosis (fat accumulation in the liver), regular alcohol consumption, certain hepatotoxic medications, and excess body weight.
Very low values also deserve attention. Recent research links very low ALT to reduced muscle mass and increased frailty, particularly after age 60. This connection between low ALT and sarcopenia is an active area of gerontological research.
ALT interpretation gains precision when combined with other hepatic markers, notably GGT. The trend over time matters more than any single reading.
Influencing Factors
Alcohol. Even moderate consumption can raise ALT. The effect is dose-dependent and generally normalizes after a few weeks of abstinence.
Medications. Acetaminophen, statins, certain anti-inflammatory drugs, and antibiotics can transiently increase ALT.
Diet. Chronic caloric excess, particularly from refined sugars and saturated fats, promotes fat accumulation in the liver. Excess fructose is specifically implicated in non-alcoholic hepatic steatosis.
Physical activity. Intense exercise can temporarily raise ALT due to muscle micro-damage. Avoid intense physical activity beyond your usual routine during the previous 24 hours. After a heavy strength-training session that is very unusual for you, wait at least 7 days before the blood draw if possible.
Body composition. Obesity, and visceral adiposity in particular, is a major factor in chronic ALT elevation. Gradual weight loss frequently normalizes values.
Age and sex. ALT values tend to decrease with age. Men typically show higher levels than women, a difference linked to muscle mass and hormonal influences.
Supplements. Certain dietary supplements, particularly those based on concentrated botanical extracts, can affect liver function. Transparency about supplement use is essential for reliable ALT interpretation.
In the Singular Formula
ALT is one of the liver markers Singular integrates into the biological profile. No formulation engine rule adjusts a dosage in response to this marker.
When ALT is in the high or very high range, the formulation engine activates a rule dedicated to liver function. This rule adjusts no dosage: it delivers dietary guidance content. GGT triggers the same rule independently, without both markers having to be elevated together. A second rule, also limited to guidance, combines this hepatic signal with elevated triglycerides.
Beyond the ruleset, two bioactives are linked to this marker. Curcumin is the majority polyphenol of turmeric rhizome. Vitamin B6 is linked on a different basis: in its active form, pyridoxal-5-phosphate, it is the coenzyme of ALT. Without it, the enzyme being measured does not work.
Measuring ALT and GGT together widens coverage: either one is enough to activate the hepatic guidance. The cross-reading with triglycerides then separates isolated hepatic stress from a broader metabolic profile.
Linked Bioactives
Scientific Studies
| Authors | Year | Type | Journal | |
|---|---|---|---|---|
| Ruhl CE, Everhart JE | 2009 | Cohort Study | Gastroenterology | View on PubMed |
Elevated serum alanine aminotransferase and gamma-glutamyltransferase and mortality in the United States population NHANES III prospective cohort (n=14,950 adults, 12-year follow-up). It tests the proposed upper ALT limits, 30 U/L in men and 19 U/L in women. No association is found with all-cause mortality (HR 1.2, CI 0.88-1.6). Liver-related mortality, by contrast, rises sharply (HR 8.2). | ||||
| Liu Z. et al. | 2014 | Meta-analysis | PLoS One | View on PubMed |
Complex association between alanine aminotransferase activity and mortality in general population: a systematic review and meta-analysis of prospective studies Meta-analysis of 12 prospective studies (206,678 people). The link between ALT and all-cause mortality is inconsistent and depends mainly on age. Before age 70, each 5 U/L increase is associated with higher mortality (HR 1.06). After age 70, the relation reverses (HR 0.91). | ||||
| Ramaty E. et al. | 2014 | Cohort Study | European Journal of Internal Medicine | View on PubMed |
Low ALT blood levels predict long-term all-cause mortality among adults. A historical prospective cohort study In this prospective cohort, low ALT independently predicts long-term all-cause mortality, even after adjustment for age, sex, and comorbidities. | ||||
| Vespasiani-Gentilucci U. et al. | 2018 | Cohort Study | Journal of Gerontology: Series A | View on PubMed |
Low Alanine Aminotransferase Levels in the Elderly Population: Frailty, Disability, Sarcopenia, and Reduced Survival In elderly populations (InCHIANTI cohort), low ALT is associated with reduced survival. This excess mortality persists after adjustment for frailty, sarcopenia and disability. Low ALT is also accompanied by low vitamin B6 status. | ||||
| Prati D. et al. | 2002 | Cohort Study | Annals of Internal Medicine | View on PubMed |
Updated definitions of healthy ranges for serum alanine aminotransferase levels Landmark study conducted in 6,835 Italian blood donors. It revises only the upper ALT limit, lowered compared with the norms of the time. Its demonstrated contribution is better detection of hepatitis C, with sensitivity rising from 55% to 76.3%. | ||||
| Visaria A. et al. | 2020 | Cohort Study | PLoS One | View on PubMed |
Association between alanine aminotransferase within the normal range and all-cause and cause-specific mortality: A nationwide cohort study In this nationwide U.S. cohort, even within the normal range, ALT in the lowest quartile is associated with increased mortality, confirming the importance of nuanced interpretation. | ||||
| Jensen M.D. et al. | 2020 | Cohort Study | Clinical Epidemiology | View on PubMed |
Alanine Aminotransferase and 20-Year Risk of Major Chronic Diseases and Death in a Healthy Cohort Aged 30 to 49 Years Cohort of healthy adults aged 30 to 49, followed for 20 years. It combines liver disease, overall cancer, ischemic heart disease and diabetes into a disease-free survival. High values and abnormally low values alike are associated with increased risk. | ||||