A question that has plagued researchers for years – why it is that low cholesterol seems to be associated with increased cancer risk – may now have an answer. The results from a new study suggest that rather than being a cause of cancer, low total cholesterol levels may actually be the result, and therefore a signal, of undiagnosed cancers. The authors publish their findings in the November issue of the journal Cancer Epidemiology, Biomarkers & Prevention.

Demetrius Albanes and his team at the National Cancer Institute wished to tease apart the relationship between cholesterol and cancer, particularly since low LDL (“bad”) cholesterol is usually considered a good thing, indicating decreased risk for heart disease and stroke. The team followed 30,000 male smokers for 18 years, tracking cholesterol levels and cancer diagnoses. Over 7,500 of the men eventually developed cancer.

A new study suggests that low cholesterol levels don't cause cancer, but they may be a sign of undiagnosed cancers.

Those with the lowest total cholesterol levels (below 230 mg/dl) had an 18% increase risk of developing cancer, which is in line with previous studies. However, when the researchers took out of the analysis all instances of cancer in the first nine years, this effect went away completely, which suggests that the increased risk associated with low total cholesterol only applied to cancers that were diagnosed early on in the study. Albanes told reporters that “[t]his finding supports the idea that the lower serum total cholesterol level we detected as a possible cancer risk factor may actually have been the result of undiagnosed cancers.”

The study also found that men who had higher levels of HDL cholesterol (the “good” variety) were at 14% reduced risk of developing cancer, even when the first nine years of cancer diagnoses were omitted. A related article in the same journal found that men with low total cholesterol (below 200 mg/dl) had a vastly reduced risk of developing high−grade prostate cancer, the most dangerous form of the disease. Both findings indicate that low cholesterol levels are still preferable and beneficial. Albanes says that more research will still be needed to pull apart further the relationship between cancer and cholesterol, particularly in women.