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
These reference ranges are derived from scientific literature and may differ from your laboratory's reference values.
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. A persistent elevation warrants closer monitoring and medical consultation.
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. It is useful to report any current medications when interpreting results.
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. It is recommended to avoid strenuous effort in the 48 hours before a blood draw.
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 plays a dual role in the Singular formulation engine. As a marker of hepatic integrity, it determines tolerance to bioactives metabolized by the liver.
When ALT falls within the high or very high range, the formulation engine activates a hepatic support protocol. N-acetylcysteine dosage is increased to support glutathione synthesis, the liver's primary cellular defense system. Reishi, a functional mushroom whose triterpenes are documented for their affinity with hepatic tissue, also receives an increased dosage. This response is triggered in parallel by GGT, another hepatic marker measured by Singular, for a cross-reading of liver function.
Beyond the ruleset, the formula includes other bioactives with documented influence on hepatic function. Sulforaphane, an isothiocyanate derived from broccoli, is studied for its role in hepatic detoxification pathways. Curcumin, a turmeric polyphenol, is the subject of meta-analyses evaluating its influence on transaminase levels.
The combination of ALT with GGT allows the formulation engine to distinguish isolated hepatic stress from a broader metabolic profile requiring an adapted response.
Linked Bioactives
Scientific Studies
| Authors | Year | Type | Journal | |
|---|---|---|---|---|
| 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 This meta-analysis of 12 prospective studies reveals a U-shaped association between ALT and all-cause mortality. Both low and high values are associated with increased risk, suggesting the existence of an optimal zone. | ||||
| 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, low ALT is associated with sarcopenia, frailty, and reduced survival. ALT may serve as an indirect marker of muscle mass. | ||||
| 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 proposing lower ALT thresholds compared to historical norms. The authors demonstrate that classic ranges include subjects with subclinical hepatic involvement. | ||||
| Younossi Z.M. et al. | 2016 | Meta-analysis | Hepatology | View on PubMed |
Global epidemiology of nonalcoholic fatty liver disease-Meta-analytic assessment of prevalence, incidence, and outcomes Meta-analysis estimating the global prevalence of non-alcoholic fatty liver disease at 25%. ALT is the first-line marker for assessing this metabolic condition. | ||||
| 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 Over 20 years of follow-up, ALT predicts the risk of diabetes, fatty liver disease, and mortality in initially healthy adults aged 30 to 49. | ||||