, according to research published in Neurology.
“Women with very low LDL cholesterol or low triglycerides should be monitored by their doctors for other stroke risk factors that can be modified, like high blood pressure and smoking, in order to reduce their risk of hemorrhagic stroke,” said Pamela M. Rist, ScD, instructor in epidemiology at Harvard Medical School, Boston. “Additional research is needed to determine how to lower the risk of hemorrhagic stroke in women with very low LDL and low triglycerides.”
Several meta-analyses have indicated that LDL cholesterol levels are inversely associated with the risk of hemorrhagic stroke. Because lipid-lowering treatments are used to prevent cardiovascular disease, this potential association has implications for clinical practice. Most of the studies included in these meta-analyses had low numbers of events among women, which prevented researchers from stratifying their results by sex. Because women are at greater risk of stroke than men, Dr. Rist and her colleagues sought to evaluate the association between lipid levels and risk of hemorrhagic stroke.
An analysis of the Women’s Health Study
The investigators examined data from the Women’s Health Study, a randomized, double-blind, placebo-controlled trial of low-dose aspirin and vitamin E for the primary prevention of cardiovascular disease and cancer among female American health professionals aged 45 years or older. The study ended in March 2004, but follow-up is ongoing. At regular intervals, the women complete a questionnaire about disease outcomes, including stroke. Some participants agreed to provide a fasting venous blood sample before randomization. With the subjects’ permission, a committee of physicians examined medical records for women who reported a stroke on a follow-up questionnaire.
Dr. Rist and her colleagues analyzed 27,937 samples for levels of LDL cholesterol, HDL cholesterol, total cholesterol, and triglycerides. They assigned each sample to one of five cholesterol level categories that were based on Adult Treatment Panel III guidelines. Cox proportional hazards models enabled the researchers to calculate the hazard ratio of incident hemorrhagic stroke events. They adjusted their results for covariates such as age, smoking status, menopausal status, body mass index, and alcohol consumption.
A U-shaped association
Women in the lowest category of LDL cholesterol level (less than 70 mg/dL) were younger, less likely to have a history of hypertension, and less likely to use cholesterol-lowering drugs than women in the reference group (100.0-129.9 mg/dL). Women with the lowest LDL cholesterol level were more likely to consume alcohol, have a normal weight, engage in physical activity, and be premenopausal than women in the reference group. The investigators confirmed 137 incident hemorrhagic stroke events during a mean 19.3 years of follow-up.
After data adjustment, the researchers found that women with the lowest level of LDL cholesterol had 2.17 times the risk of hemorrhagic stroke, compared with participants in the reference group. They found a trend toward increased risk among women with an LDL cholesterol level of 160 mg/dL or higher, but the result was not statistically significant. The highest risk for intracerebral hemorrhage (ICH) was among women with an LDL cholesterol level of less than 70 mg/dL (relative risk, 2.32), followed by women with a level of 160 mg/dL or higher (RR, 1.71).
In addition, after multivariable adjustment, women in the lowest quartile of triglycerides (less than or equal to 74 mg/dL for fasting and less than or equal to 85 mg/dL for nonfasting) had a significantly increased risk of hemorrhagic stroke, compared with women in the highest quartile (RR, 2.00). Low triglyceride levels were associated with an increased risk of subarachnoid hemorrhage, but not with an increased risk of ICH. Neither HDL cholesterol nor total cholesterol was associated with risk of hemorrhagic stroke, the researchers wrote.