Recent research indicates that certain blood markers, tested during routine doctor visits, could reveal unexpected insights about the risk of developing colorectal cancer at a young age.
In a study by Epic Research, it was found that adults under 45 with lower levels of two liver enzymes—aspartate transaminase (AST) and alanine transaminase (ALT)—were more likely to be diagnosed with early-onset colorectal cancer than those with higher levels. This analysis was published recently and has raised some eyebrows.
Kersten Bartelt, a researcher involved in the analysis, noted, “The direction was a little counterintuitive. Usually, high liver enzyme levels are what we watch for, so it was surprising to see low AST and ALT tied to an increased risk of early-onset colorectal cancer.”
However, medical professionals advise that younger adults with low AST or ALT levels shouldn’t be overly alarmed, and there’s no change in screening recommendations yet.
This research suggests a connection but doesn’t imply that low enzyme levels cause cancer or necessitate an immediate colonoscopy. The findings are preliminary and warrant further exploration to better understand the reasons behind the rising colorectal cancer cases among younger populations.
Bartelt remarked, “Our study shows the association but wasn’t designed to discover why. Low AST and ALT might reflect factors like lower muscle mass or nutritional status. We hope this prompts others to investigate further.”
The results are particularly striking since high levels of these enzymes often indicate a struggling liver, and elevated markers can signal various health issues. They are routinely checked in blood tests because they can highlight early liver problems even without noticeable symptoms.
“AST and ALT aren’t numbers we would recommend anyone try to elevate,” Bartelt added. “And our findings don’t indicate changing them would affect cancer risk. They likely reflect broader physiological aspects, like nutritional health, hence the focus should be on overall well-being rather than fixating on a single lab result.”
In addition to AST and ALT, the researchers also looked into triglyceride and cholesterol levels but found no correlation with early-onset colorectal cancer.
The rise in colorectal cancer among younger adults has been a concern for the medical community. This form of cancer has now become the leading cause of cancer deaths in people under 50 in the U.S.
Dr. Marc Fenster, a gastroenterologist who was not part of the study, stated, “Whenever there’s a focus on colon cancer, especially early-onset cases, we need to understand the reasons. Identifying markers to help target those needing screenings would be beneficial.”
How to Lower Your Risk of Colorectal Cancer
- Get screened. Most colorectal cancers start as precancerous polyps that can be detected and removed through colonoscopy.
- Don’t smoke.
- Maintain a healthy body weight.
- Stay physically active.
- Limit alcohol intake.
- Reduce red meat and processed foods while increasing fiber intake from whole grains, fruits, and vegetables.
Fenster emphasized that the broader discussion around early-onset colorectal cancer encompasses various factors, including family history, dietary habits, and lifestyle choices. Yet, none of these fully account for the rising incidence rates. This study could enhance the discussion by introducing how routine metabolic and nutritional markers might provide additional insights.
Even though the study signifies a “signal” worth examining further, it doesn’t establish low AST or ALT levels as definitive risk factors for early-onset colorectal cancer.
Fenster further warned that while the study is noteworthy, it should not alter current screening protocols. “Individuals shouldn’t worry about low AST or ALT levels unless they have other concerning symptoms or a family history,” he said, stressing that if someone is otherwise healthy, they shouldn’t panic.
In the U.S., the general guideline is for average-risk individuals to begin colorectal cancer screenings at age 45, while those at higher risk may start earlier. There’s already a blood test option available for screening.
In a significant update, the American Cancer Society recently recommended blood-based screening tests for adults 45 and older at average risk, particularly for those who haven’t undergone traditional visual exams or stool tests.
The Shield test, a blood-based screening tool, has been introduced, but it is not a part of standard lab tests. While colonoscopies remain the most reliable method for screening, blood tests can serve as preliminary tools. However, a positive Shield test does not provide a conclusive diagnosis; a follow-up colonoscopy is necessary.
Blood tests “do not replace colonoscopy,” Fenster reiterated.
For their study, Bartelt and her team analyzed data from more than 11,000 individuals aged 18 to 44 who underwent their first colorectal screening between 2017 and 2025 and had at least one AST or ALT test within three years before screening.
It remains unclear why some of these patients had colonoscopies ahead of the typical screening age, which could relate to family histories, present symptoms, or other risk factors.
“It’s likely these patients had symptoms and were undergoing diagnostic colonoscopies rather than routine screenings,” Bartelt speculated.
The research compared individuals diagnosed with colorectal cancer within a year of their screening to those who were not diagnosed with the disease.
Results revealed that adults with AST levels below 14 units per liter had a 65% greater likelihood of early-onset colorectal cancer compared to those with levels between 14 and 29. Likewise, those with ALT levels under 14 had a 68% higher likelihood.
On the contrary, levels of AST or ALT above 30 correlated with a lower risk—22% lower for AST and 29% lower for ALT.
The researchers used the 14 to 29 range as a baseline because it represented mid-range levels in their findings.
“AST and ALT levels can vary greatly from person to person and can fluctuate over time due to factors like physical activity, muscle mass, illness, or medication,” Bartelt pointed out.
They also examined how changes in AST and ALT levels over time, particularly increases leading up to screening, impacted colorectal cancer risk.
The findings showed that increasing AST levels resulted in a 27% lower likelihood of cancer, while rising ALT levels indicated a 26% lower likelihood compared to stable values. Conversely, drops in AST or ALT did not demonstrate a notable correlation with cancer risk.
It’s important to note that what is classified as “normal” for AST or ALT levels can vary among different medical practices.
Each testing lab establishes its own reference ranges, but the low levels identified in this study are often viewed as normal in clinical settings. Dr. Daniel Sussman from the University of Miami expressed caution about interpreting these findings as significant cancer risk markers, noting that unexpected results require thorough validation.
Another study published in the International Journal of Cancer also found that high AST and ALT levels, which largely remained within normal limits, were linked to a lower risk of colorectal cancer, based on data from over 375,000 individuals in the UK.
Despite differing focuses, both studies demonstrated an inverse relationship between liver enzyme levels and colorectal cancer risk.
“The data highlight the need for deeper understanding of how liver function changes relate to colorectal cancer,” noted Mingyang Song from Harvard, an author of the previous study.
Song remarked that lower AST/ALT levels in generally healthy participants could indicate reduced liver functionality and a heightened susceptibility to cancer-causing agents, though he stressed that clinical guidelines should not hinge solely on these enzyme levels.
In agreement, Bartelt remarked that low AST or ALT results alone are not cause for alarm.
“We need additional research to decide how low AST or ALT values should influence early screening recommendations. Staying current on screenings—routine at age 45 or earlier with risk factors—remains crucial,” she said.
Sussman added that he would not recommend anyone try to raise their AST or ALT levels and reiterated that this new study doesn’t change outcomes regarding colorectal cancer screening.
He emphasized that he would not advocate for screening adults under 45 strictly based on their AST or ALT levels.
Ultimately, “the analysis seems exploratory,” he concluded, calling for more research rather than adjustments to current norms in assessing liver enzyme levels or determining screening needs for colorectal cancer.
One key question for future research is how these findings translate to a broader population, according to Caleb Cox of Epic, who led the analysis team.
The increase in colorectal cancer cases among younger individuals remains an unclear area. “We don’t believe these low levels are the cause. They might indicate a broader issue contributing to the rise in colorectal cancer,” Cox remarked.
