High total cholesterol levels may be linked to an increased risk of some cancers but a lower risk of others, according to a new Korean study.
"We do not have a clear understanding" of how cholesterol might directly influence cancer risk, said Dr Cari Kitahara from the US National Cancer Institute said.
Dr Kitahara, the lead author of a report on the study, added that the cholesterol itself might not be what's affecting people's cancer risk. Instead, lifestyle choices or other heath conditions might make people with high cholesterol more or less vulnerable.
Previous smaller studies have given conflicting answers to the question of whether cholesterol levels might affect a person's chance of getting cancer.
The current study, published in the Journal of Clinical Oncology, included about 1.2 million Korean men and women who had standard fasting cholesterol tests.
At the start of the study, the men's average age was 45, and their average total cholesterol level was 191 mg/dL. The women's average age was 49, and their average cholesterol level was 194 mg/dL.
Over an average of nearly 13 years, roughly 7% of participants developed some form of cancer - most commonly stomach cancer (roughly 2%), followed by lung cancer and liver cancer (less than 1% each).
When the researchers analysed everyone who developed cancer, regardless of the type, they found that people with a high total cholesterol level were more likely to get the disease.
Risk not that high
The extra risk wasn't very large, though. In men, the odds of getting cancer were 7.9% for those with the highest total cholesterol, compared to 7.1% for those with the lowest cholesterol.
Women with high cholesterol had a 6.3% of getting cancer, while women with low cholesterol had a 5.1% chance.
Looking more closely, the researchers also saw that the relationship of cholesterol and cancer risk varied by organ. For example, compared to men with total cholesterol levels less than 160 mg/dL, men with high levels were more likely to develop prostate cancer and colon cancer but less likely to get cancer of the liver, stomach or lung.
And compared to women with low cholesterol, women with high cholesterol were more likely to get breast cancer and less likely to get liver cancer.
But after adjustment for a range of health-related factors, including weight, blood pressure, smoking status and alcohol consumption, high cholesterol seemed to have the opposite effect. Overall, it lowered people's cancer risk. In that analysis, people with the highest levels of cholesterol were between 9% and 16% less likely to get cancer.
Why we need cholesterol
Cholesterol is involved in the body's production of hormones; it could be through these processes that cholesterol increases or decreases the risk of different kinds of cancer, Dr Kitahara said.
Another possible explanation is that people with high cholesterol are more likely to be taking statins, and these drugs themselves may increase or decrease the risk of certain cancers.
But Dr Kitahara said that was unlikely to explain this study's findings because not many people were taking statins.
For now, Dr Kitahara said, "more studies are needed to confirm or refute these findings."
(Reuters Health, Genevra Pittman, March 2011)
HDL and LDL