Insulin resistance originates from several factors, including genetics, a sedentary lifestyle and obesity, according to background information in the article. The condition contributes significantly to the risk of cardiovascular disease, but whether it predicts ischemic stroke (interruption in blood flow to the brain due to a blood clot or another artery blockage) is still a matter of debate.
One widely used tool to estimate insulin sensitivity is the homeostasis model assessment (HOMA), calculated using fasting blood glucose and fasting insulin levels. The Miller School team assessed insulin resistance using HOMA for 1,509 non-diabetic participants in the Northern Manhattan Study, a study assessing stroke risk, incidence and prognosis in a multi-ethnic urban community. Participants were followed for an average of 8.5 years.
During the follow-up period, vascular events occurred in 180 participants, including 46 who had fatal or non-fatal ischemic strokes, 45 who had fatal or non-fatal heart attacks and 121 who died of vascular causes.
Individuals in the top one-fourth (quartile) of HOMA index had an increased risk of stroke compared to those in the other three quartiles of the HOMA index. Adjusting for established cardiovascular risk factors—including glucose level, obesity and metabolic syndrome—did not diminish the association. The relationship between insulin resistance and the risk of first stroke was stronger in men than women but did not vary by racial or ethnic group.
Individuals in the top quarter of insulin resistance had a 45 percent greater risk of any type of vascular event. However, insulin resistance was not associated with heart attack or vascular death separately.
“This epidemiological study shows that pre-diabetes or insulin resistance is very important among people with non-diabetes, as it is clearly associated with increased risk of stroke,” said Tatjana Rundek, M.D., Ph.D., associate professor of neurology and lead author of the study. “This knowledge can really help assess and target people with an increased risk of stroke and not yet diabetic. We would need well designed clinical trials to determine how to treat these people moving forward, but for now the new knowledge may prompt the physician to treat the risk factors in a patient with pre diabetes much more aggressively.”
“There are several possible reasons for the stronger effect of insulin resistance on the risk of ischemic stroke than of myocardial infarction in the present study compared within other studies,” the authors write. It may be because individuals with a history of heart attack were excluded from this study, or because factors associated with insulin resistance—including high blood pressure, high triglyceride levels and low HDL or “good” cholesterol levels—are more significant risk factors for stroke than for heart attack.
“The Northern Manhattan study continues to shed light on important and novel risk factors for stroke, cardiovascular diseases, and cognitive decline among those population groups at greatest risk for vascular disease,” said Ralph Sacco, M.D., M.S., professor and chair of neurology, senior author of the study, and founder and principal investigator of the Northern Manhattan study. “The National Institute of Neurological Disorders and Stroke funded study is in its 18th year and involves multiple investigators and students at the Miller School and Columbia University.”
Clinton B. Wright, M.D., M.S., associate professor of neurology, Hannah Gardener, Sc.D., assistant scientist in the Department of Neurology, and Ronald Goldberg, M.D., professor of medicine, were all authors of the study.