People who significantly cut their cholesterol levels with statins may raise the risk of cancer, a study says.
Statins can reduce the risk of having a heart attack
The study of 40,000 people found those with little of the "bad" cholesterol LDL saw one more cancer case per 1,000 than those with higher levels.
The Boston-based researchers could not say if this was a side-effect of the statin or due to the low cholesterol.
They also write in the Journal of the American College of Cardiology that the benefits of statins outweigh the risks.
"The analysis doesn't implicate the statin in increasing the risk of cancer," says lead author Richard Karas of Tufts University School of Medicine in Boston. "The demonstrated benefits of statins in lowering the risk of heart disease remain clear.
"However certain aspects of lowering LDL with statins remain controversial and merit further research."
Researchers looked at the summary data from 13 trials of people taking statins - a total of 41,173 patients.
They examined the relationship between low, medium and high doses of statins and rates of newly diagnosed cancer.
Higher rates of the disease - which were not of any type or location - were observed in the group with the lower levels.
The authors noted their findings were particularly important at a time when more and more trials show significant reductions in LDL levels can greatly benefit cardiovascular health.
Cancer Research UK was wary of the study.
Cancer information officer Dr Alison Ross said: "The findings of this study should be treated with caution - it is based on summary data from previous trials and, as the authors point out themselves, it does not prove that low LDL cholesterol levels can increase cancer risk.
"Much more research is needed before any firm conclusions can be made."
The British Heart Foundation said they had long known of a relationship between low cholesterol and cancer.
"While this highlights an association between low levels of LDL and cancer, this is not the same as saying that low LDL or statin use increases the risk of cancer," said June Davison, cardiac nurse.
"There is overwhelming evidence that lowering LDL cholesterol through statins saves lives by preventing heart attacks and strokes. These findings do not change the message that the benefits of taking statins greatly outweigh any potential risks."