Your kidneys are two reddish, bean-shaped organs located on either side of your spine in the middle of your back. Their main job is to filter your blood. Each kidney contains about a million tiny filters that can process around 40 gallons of fluid every day—about enough to fill a house’s hot water heater. When blood passes through the kidney, the filters sift and hold onto the substances your body might need, such as certain nutrients and water. Harmful wastes and extra water and nutrients are routed to the nearby bladder and flushed away as urine.
Your kidneys also produce several hormones. These hormones help to control your blood pressure, make red blood cells and activate vitamin D, which keeps your bones strong.
We all lose a little of our kidney function as we get older. People can even survive with just one kidney if they donate the other to a friend or family member. But when kidney function drops because of an underlying kidney disease, it’s something to be concerned about. Toxins and extra water can build up in your blood. Falling hormone production can cause other problems. About 1 in 10 adults nationwide, or about 20 million people, have at least some signs of kidney damage.