NEW YORK (Reuters Health) - High cholesterol 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 U.S. National Cancer Institute in an email to Reuters Health.
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 likely to get certain cancers.
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 a standard cholesterol test after fasting overnight.
The investigators calculated everyone's "total cholesterol" level - a combination of their "bad" LDL cholesterol and "good" HDL cholesterol. Then they kept track of all study participants for an average of almost 13 years, using a cancer database and hospital admission files to determine which of them developed cancer later on.
At the start of the study, the men's average age was 45, and their average total cholesterol level was 191 milligrams per deciliter (mg/dL) of blood. The women's average age was 49, and their average cholesterol level was 194 mg/dL.
According to the U.S. National Institutes of Health, a "desirable" total cholesterol level is one that's below 200 mg/dL. Levels between 200 and 239 mg/dL are considered "borderline," and levels of 240 mg/dL or above are "high."
Overall, about seven of every 100 people in the study developed some form of cancer. The most common type was stomach cancer (about two of every 100 people), followed by lung cancer and liver cancer (each in about one of every 100 participants).
When the researchers analyzed 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.
The extra risk wasn't very large, though. In men, the odds of getting cancer were 7.9 percent for those with the highest total cholesterol, compared to 7.1 percent for those with the lowest cholesterol; in other words, a difference of less than one percent.
Women with high cholesterol had a 6.3 chance of getting cancer, while women with low cholesterol had a 5.1 percent chance - slightly more than a one percent difference in risk.
Looking more closely, the researchers also saw that the relationship of cholesterol and cancer risk varied in different parts of the body. For example, compared to men with low 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 liver cancer, stomach cancer or lung cancer.
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 when the authors took into account a range of health-related factors, including people's weight, blood pressure, cigarette smoking 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 percent less likely to get cancer.
Cholesterol plays an important role in determining what flows in and out of cells in the body and is also involved in the body's production of hormones such as estrogen and testosterone. It could be through these processes that cholesterol increases or decreases the risk of different kinds of cancer, Kitahara said.
Another possible explanation for the link between cholesterol and cancer is that people with high cholesterol are more likely to be taking cholesterol-lowering drugs, such as statins, to lower their risk of heart problems. These drugs themselves may increase or decrease the risk of certain cancers. But Kitahara said that was unlikely to explain this study's findings because not many people were taking statins.
The results don't mean that people can lower their risk of cancer by lowering their cholesterol with drugs or diet changes, though.
Kitahara said that "more studies are needed to confirm or refute these findings" - and in the meantime, people with questions about their cholesterol should talk with their doctor.
SOURCE: http://bit.ly/gIETVt Journal of Clinical Oncology, online March 21, 2011.
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