More than half a million people living in nine countries in Europe took part in the research, designed to explore the impact of diet on cancer risk.
The analysis revealed that people with the highest blood levels of HDL cholesterol had the lowest risk for developing colon cancer. The association appeared to be independent of other risk factors for the cancer, such as obesity and poor diet.
Each rise in HDL of around 16 mg/dL was associated with a 22% reduction in colon cancer risk, after adjusting for diet, lifestyle, and weight.
“If these findings are confirmed, HDL levels may be a useful indicator of colon cancer risk, along with other risk factors that are already known to us,” study co-researcher Bas Bueno-De-Mesquita, MD, PhD, tells WebMD.
Colon Cancer, HDL, and Metabolic Syndrome
An HDL of less than 40 mg/dL for men and 50 mg/dL for women is considered low by the American Heart Association, while levels at or above 60 mg/dL are considered to convey some protection against heart disease.
Smoking, lack of exercise, and being overweight or obese are all associated with lower HDL levels.
These risk factors include: having excess belly fat (abdominal obesity); high blood pressure; insulin resistance; high blood triglyceride levels; and HDL levels below 40 mg/dL for men and 50 mg/dL for women.
People with three or more of these risk factors are considered to have metabolic syndrome.
In the newly published study, Bueno-De-Mesquita and colleagues examined the impact of cholesterol and triglycerides on colon cancer risk, independent of other risk factors associated with metabolic syndrome.
The study included 520,000 participants in the European Prospective Investigation into Cancer (EPIC) trial.
Over the course of the study, 1,238 cases of colorectal cancer were identified. An equal number of study participants matched for age, sex, and nationality with the cancer patients were included in the analysis.
Blood samples and dietary questionnaires provided at enrollment were compared to determine if major differences existed between the colorectal cancer patients and people who did not develop the cancer.
Overall, the colorectal cancer patients were heavier and reported being less physically active than non-patients.
Just two blood levels -- HDL and another blood fat known as apolipoprotein A-1 (ApoA) -- were found to be associated with colon cancer risk. But after excluding patients with the shortest follow-up, only higher HDL was associated with a reduction in colon cancer risk.
No association was seen between levels of either blood fat and rectal cancer.
The study is published online in the journal Gut.
Low HDL and Inflammation
Bueno-de-Mesquita says low HDL levels may increase colon cancer risk by promoting systemic inflammation. High HDL has been linked in previous studies to high levels of proteins that prevent inflammation.
“It is important to point out that HDL may just be a bystander or indicator of unknown factors that influence the risk for this disease,” he says.
Edward Giovannucci, MD, professor of nutrition and epidemiology at the Harvard School of Public Health, calls the new research “interesting and well done.”
Giovannucci has also studied the impact of metabolic syndrome on colon cancer risk.
“This study suggests that we should look at HDL cholesterol more closely, but I don’t think it is a closed case,” he told WebMD. “Other abnormalities may be as important, or perhaps more so.”
He agrees the possible impact of HDL on colon cancer risk is deserving of further study, but adds that higher levels of HDL may prove to be little more than a marker for metabolic syndrome.
“HDL cholesterol may be acting as a more stable and reliable indicator of metabolic syndrome [than insulin resistance]. But whether it is the direct causal factor requires more work,” he says.