Atherosclerosis is characterized by thickening of the artery walls, and the narrowing of the blood vessels as cholesterol is deposited in the lining of the arteries. It is the major cause of cardiovascular disease including ischemic heart disease (heart attacks) and stroke. Although, historically, there has been a widespread perception that higher levels of testosterone might increase the risk of atherosclerosis, the evidence from research does not support this. In observational studies, higher testosterone levels have been correlated with more favorable cardiovascular risk factors, and supplementation with testosterone to bring older men into the normal range for healthy younger men appears to improve several cardiovascular risk factors, and may slow the progression of atherosclerosis.