ALT (alanine aminotransferase) is an enzyme released into the bloodstream when liver cells are damaged. Measuring serum ALT is a standard way to assess liver injury.
A randomized, single-blind, placebo-controlled study published in the Journal of the American Medical Association (July 5, 2006; Vol. 296, No. 1) examined the effect of acetaminophen taken at recommended doses on liver enzymes. The study included 145 healthy adults in a diet-controlled inpatient setting.
Participants received either 4 grams of acetaminophen per day (the maximum recommended daily dose) or a placebo for 14 days. Nearly 19% of those taking acetaminophen experienced elevations in ALT levels to almost five times the upper limit of normal, indicating liver cell injury. No such increases were observed in the placebo group.
Takeaway
Even when used exactly as directed, acetaminophen can cause measurable liver injury in a significant subset of healthy individuals, as reflected by marked increases in ALT.
