High cholesterol is a major risk factor for death from heart disease, but its impact on stroke death is less clear, concludes a new study in a finding that startled even the researchers.
The study, published in The Lancet medical journal, was an analysis of 61 previous studies that involved almost 900,000 adults. The studies clearly showed that people of all ages who had lower total blood cholesterol levels had a lower heart disease death rate.
More specifically, they found that the ratio of total cholesterol to HDL cholesterol -- the so-called good cholesterol -- was a much stronger predictor of heart disease risk than total cholesterol alone.
But the researchers found no relationship between total cholesterol levels and risk of stroke death, especially at older ages.
In fact, in patients aged 70-89 years -- particularly for those with high systolic blood pressure -- higher cholesterol was associated with lower stroke mortality--a finding that the authors cannot explain.
Previous research has consistently shown that cholesterol-lowering drugs, called statins, substantially reduce stroke risk.
One of the researchers, Dr. Sarah Lewington of the University of Oxford in Britain, admits her team is baffled. She says much more research is needed to explain the findings.
She addes that patients taking statins should certainly not consider going off their medications.
"Irrespective of the explanation, however, treatment should be guided principally by the definitive evidence from randomised trials, that statins substantially reduce not only coronary event rates but also total stroke rates in patients with a wide range of ages and blood pressures," her team writes.
In a commentary accompanying the study, two experts in France, Drs. Pierre Amarenco and Gabriel Steg of Bichat-Claude Bernard University Hospital in Paris, wrote that a link between cholesterol and stroke risk "probably exists."
"Because most of the benefit of statins in preventing cardiovascular events can be ascribed to the LDL reduction, it is puzzling that LDL cholesterol is not associated with stroke risk," they wrote.
They added that "there is good evidence that lowering blood cholesterol with statins reduces stroke risk."
