A large study finds that low cholesterol levels are associated with an increased risk of hemorrhagic stroke.
Tobias Kurth presented data from the Women's Health Study at the International Stroke Conference (2/06) analyzing cholesterol levels and risk of hemorrhagic stroke. The Women's Health Study is a large study of female health professionals. Of the 39,876 participants, 28,345 women provided baseline blood samples. Dr. Tobias et al. analyzed these baseline cholesterol levels as well as the number of hemorrhagic strokes occurring in these women an average of 10 years later. A total of 65 women experienced a hemorrhagic stroke in this time. Various cholesterol measures were analyzed, including total cholesterol, LDL cholesterol, HDL cholesterol, triglycerides, and total cholesterol/HDL ratio. (For an explanation of cholesterol types, click here). Results were complex, but it was overall found that low LDL, triglycerides, and total cholesterol/HDL ratio were associated with a higher risk of hemorrhagic stroke. A high HDL cholesterol level was also associated with high hemorrhagic stroke risk, although the relationship was complex (taking on a 'U'-shape with both very high and very low levels being bad, intermediate levels being beneficial).
Nearly everything you read regarding stroke and heart attack risk these days indicates that low total cholesterol reduces your chances of having an ischemic stroke or heart attack. This study does nothing to challenge this notion, but it begins to explore the other side of the coin. Is there a lower limit of cholesterol, below which one shouldn't go? The ischemic stroke literature supports bringing LDL (so called 'bad' cholesterol) down below 100mg/dL in any patient who has suffered an ischemic stroke. The cardiac literature supports pushing patients with coronary heart disease below 70mg/dL. But no one knows just how low you can go to continue to achieve an overall benefit. Clearly the lowest levels of LDL and total cholesterol in this study were associated with more hemorrhagic strokes, but if the overall risk of an ischemic stroke remains higher than that of a hemorrhagic stroke, the benefits of low cholesterol might still outweigh the risk.
Perhaps the researchers involved in the Women's Health Study have the answers at their fingertips. If they simply review the number of deaths (both overall, and due to vascular disease) stratified according to cholesterol level, they would be able to determine if people with the lowest cholesterol levels had a higher or lower chance of death overall and death due to vascular causes. This would begin to give us insight into how seriously to take the risk of hemorrhagic strokes due to low cholesterol levels.