These improved AIDS treatments have cut the death rate substantially. The problem is much worse in other parts of the world. Two-thirds of the world's 33 million AIDS victims live in Africa, according to the World Health Organization. The narrowed arteries block blood flow to the heart is blocked, causing heart attack. Coronary bypass surgery was first performed in 1967 as a treatment for atherosclerosis.
Surgeons graft a piece of a leg vein to the aorta to bypass the blockage.
Another less radical technique is angioplasty, which uses an inflatable catheter to expand the cardiac artery and remove the blockage. Meanwhile, research continues on the long-term effects of dietary cholesterol. Nutrition Food supplies have improved throughout the century, improving health and resistance to disease. For example, rickets, characterized by curved leg bones, was found to be due to a deficiency in vitamin D. Pellagra, which causes dementia and gastrointestinal sickness, was found to be caused by a lack of niacin. As the various vitamins were identified, they often were added to food.