Researchers at the Molecular Cardiology Research Institute at Tufts Medical Center in Boston conducted an analysis of 24 trials that investigated the pros and cons of cholesterol treatment interventions, primarily statin therapy. The research team looked at high-density lipoprotein (HDL) cholesterol, the “good” cholesterol that is protective against heart disease, and the incidence of cancer.
Their analysis showed that the higher the HDL cholesterol levels, the lower the rate of cancer. There was a 36% lower rate of cancer for every 10 mg/dL higher level of HDL. This association held even after adjusting for other factors that can influence both cholesterol and cancer development, including age, body mass index, diabetes, sex, smoking status, and low-density lipoprotein cholesterol (LDL), the “bad” cholesterol that clogs arteries and contributes to heart disease.
The findings were published in the June 22 issue of Journal of the American College of Cardiology and were based on 145,743 patients with a median follow-up of five years, during which 8,185 cases of cancer occurred.
Though the findings do not suggest a cause-and-effect relationship between cholesterol and cancer, it does build on an existing body of evidence that shows an association between the unhealthy type of cholesterol and an increased risk of cancer.
“There is a strong and important relationship between the level of good cholesterol that people have in their blood and their risk of getting cancer. This supports another potentially important role for HDL in the body,” says study researcher Richard Karas, MD, PhD, executive director at the Molecular Cardiology Research Institute.
HDL is responsible for transporting cholesterol to the liver and keeping cholesterol moving throughout the body. Higher HDL is associated with a twofold to threefold reduced risk for heart disease. The biological mechanisms in which HDL might also protect from cancer is unclear, the researchers say. Some theories are:
- HDL may have antioxidant properties that protect against cell damage. Cell damage increases the risk of abnormal cell growth or cancer development.
- HDL may affect the immune system and help the body better defend itself against cancer.
- HDL may have anti-inflammatory properties that quell cancer cell growth and help maintain a biological environment in which cancer cells cannot thrive.
Further research is needed to tease out these biological behaviors, says Karas. In the meantime, patients can still benefit from getting their cholesterol levels regularly checked and learning the values of both their LDL and HDL numbers. “Patients need to be informed and understand what each cholesterol number means for their overall health and risk of disease,” he says.
Bad Cholesterol: Cancer Risk Factor?
In an accompanying editorial, Jennifer Robinson, MD, MPH, a professor of epidemiology and medicine at the University of Iowa College of Public Health in Iowa City, writes that low HDL levels could help clinicians identify who is at risk.
“This study suggests that HDL might be an important marker for all lifestyle risk factors we know contribute to both heart disease and cancers -- smoking, obesity and inflammation, for example,” she writes. “Since low HDL appears to be a marker for chronic disease risk, this is just another reason why we need to emphasize improved lifestyle among these patients.”
Robinson also notes it is unclear whether high HDL may be protective or if low HDL may indicate risk of disease. “Low HDL levels may simply be a reflection of chronic conditions that increase inflammation and insulin resistance, which may directly influence atherosclerosis and carcinogenesis,” she writes.
Separately, the researchers conducted a secondary analysis of the same data to look at the impact of other cancer risk factors -- age and body mass index (BMI), a measurement of height and weight. Both factors have also been linked to cancer risk. Karas and his team found a significant and direct association between both age and BMI and cancer; every five-year increase in age was associated with a 33% relatively higher cancer rate, and every 1 kg/m2 increase in BMI was associated with a 21% relatively higher cancer rate. The findings affirm the notion that age and weight influence cancer risk.