Kidney Disease and Your Heart: The Hidden Link

When you have kidney disease, it might not occur to you to have your heart checked out.  Or, if you have heart disease, you might not think to have your kidneys tested.  As it turns out, checking both your heart and your kidneys is a good idea if you have either kind of health problem.

Why?  Because diseases that affect the kidneys can also damage your heart—and vice versa.  In fact, many doctors think of the heart and kidneys as one interlinked body system rather than separate organs.ⁱ

Having both heart and kidney disease can cause 20 times the risk of death from heart problems than either problem alone.ⁱⁱ In looking at more than 18,000 people, a decline in kidney function predicted a 62% higher risk of death from heart failure.ⁱⁱⁱ Heart disease happens very early in the course of kidney disease—so even just a small decline in kidney function should trigger efforts to help protect your heart.^iv

Your Heart and Kidneys Never Sleep

While you can take a break after a hard day, your heart can’t.  Its job is to pump oxygen-rich blood from your lungs to each cell in your body, minute after minute, day after day.  If your heart beats at the average rate of about 75 times a minute, this means more than 39 million beats a year!

With each heartbeat, blood is pushed through your kidneys for filtering.  Though your two kidneys are each just about the size of your closed fist, they process about 200 quarts of blood per day to make about two liters of urine.^v To do their work, your kidneys need a constant supply of blood at a normal pressure.  Too little blood or too little pressure can cause acute, sudden kidney failure.  Too much blood or too much pressure can lead to scarring that can cause chronic, permanent kidney disease.

The Low Side of High Blood Pressure

Healthy kidneys “work” with your heart to control your blood pressure.  Any time your blood pressure falls, kidneys releasethe enzyme renin into your blood.  Renin signals your liver to make the hormone angiotensin, which tells blood vessels to constrict—raising blood pressure.  This renin-angiotensin system (RAS) acts on your heart and your kidneys.  An overactive RAS can lead to kidney problems.  Cells may grow too fast or too slowly, causing inflammation, hardening of the arteries, and blood clots.^vi

High blood pressure is quite common in the United States, and can damage your heart and your kidneys. High blood pressure causes tiny tears in the flexible lining of your blood vessels.  The scars that form make vessels walls stiff.^vii When this happens, your heart has to work much harder to pump blood through the damaged vessels.  These damaged vessels may not be able to deliver enough blood to organs so this can lead to both heart and kidney failure.

What’s Blood got to do with it?

A number of health problems that involve your blood can harm both your heart and your kidneys.  One is anemia—a shortage of oxygen-carrying red blood cells.  Kidneys make erythropoietin (EPO), the hormone that tells your bone marrow to make red blood cells.  As the kidneys fail, less EPO is made, so you make fewer red blood cells.  With fewer red blood cells, your body does not get enough oxygen.  Anemia can speed up the rate of kidney failure.

Other blood-related risk factors for heart and kidney problems include:

1. High blood levels of cholesterol – a waxy fat that can clog your arteries and lead to blood clots that can damage your heart or kidneys
2. Inflammation – your body’s response to infection or other injury, which can cause swelling and damage in your blood vessels
3. Blood vessel calcification – a build up of stone-like crystals that can occur when kidney disease throws off the balance of calcium and phosphorus in your blood

The human body is very complex, and doctors are actively studying even more reasons why the heart and kidneys affect each other.

What You Can Do

To help your kidneys and your heart work as well as possible, do what you can to keep the normal balance inside your body.

The main job of your kidneys is to maintain homeostasis—a constant environment inside your body.  Kidneys have built in sensors.  At any given moment, healthy kidneys ensure that blood levels of water, salts, and other key chemicals are in perfect balance.  When they begin to fail, this very precise system starts to fall apart.  While we may not yet know exactly why this affects the heart, we know that it does.  Here are some things you can do:

1. Control your blood pressure.  Blood pressure pills, diet, and exercise can help reduce the stress on your blood vessels.  This can help keep both your kidneys and your heart healthy.  You may find that a low-salt diet can help make it easier to hit the blood pressure target your doctor gives you.
2. Learn your glomerular filtration rate (GFR).  Based on your age, race, sex, and blood level of creatinine (a waste removed by healthy kidneys), your GFR is an estimate of how well your kidneys work.  GFR is used to put chronic kidney disease into one of five stages.  Finding out that you have loss of kidney function can give you time to get treatment so to protect your kidneys and heart at the same time.  In many cases when kidney disease is found early enough kidney failure can be delayed or prevented.
3. Keep your phosphorus in line.  If you have kidney disease, your doctor may prescribe phosphate binders for you to take with meals and snacks.  These drugs attach to phosphorus molecules like magnets and pull them out of your body—so you can keep the right balance of calcium and phosphorus.  Too much phosphorus can lead to high levels of calcium being deposited in soft tissues such as blood vessels.  Taking binders can help keep this from happening.
4. Ask your doctor to test you for anemia.  Most people who have some level of kidney problem also have anemia, which can be found with a simple blood test.  Sometimes the symptoms of anemia—feeling very tired, weak, or cold all the time; fuzzy thinking; pale skin, lips, gums, and nail beds, etc.  These symptoms can come on so slowly that you don’t really notice.  If you have anemia, getting treatment can give you more energy and help your heart and kidneys.

Forewarned is Forearmed

Knowing that kidney disease and heart disease go hand-in-hand can help you know what to look for.  You and your doctor can work together and take action to prevent health problems.

The good news is that both kidney disease and heart disease can be treated to help you stay healthy.

Part 2 of Kidney Disease and Your Heart: The Hidden Link focuses on diabetes.