People with two healthy kidneys are said to have 100% of their kidney function. A drop in how the kidneys function can increase a person's risk of heart and artery problems, two new studies suggest. One study kept track of 4,378 elderly people for 8 years. About one-quarter of them had a decline in kidney function. They were more likely to have a heart attack or develop heart failure than people without kidney problems. They also were more likely to develop peripheral artery disease. The other study included 13,029 people. All were age 45 to 64 when the study began. Researchers kept track of them for 9 years. Some people's kidney function dropped by more than 5.6% per year. People in this group had a higher risk of developing heart disease. They also were more likely to die early than people with stable kidney function. Both studies will appear in the Journal of the American Society of Nephrology. They were published online November 5.

By Robert H. Shmerling, M.D.
Harvard Medical School

What Is the Doctor's Reaction?

When I was a medical intern, my supervising resident let me in on this little known secret:

The dumbest kidney is smarter than the smartest intern.

This was not meant to be a slight to interns like me. It was more about how remarkable kidneys are. They do more than most people realize. For example, kidneys help us:

• Retain fluid when we are dehydrated and get rid of excess fluid
• Regulate electrolytes such as sodium and potassium
• Maintain the proper acid level in the blood
• Get rid of waste products while holding on to things the body needs, such as protein
• Avoid dangerously low blood pressure
• Avoid anemia
• Regulate minerals critical for bone health

When the kidneys are not functioning properly, medicines can help. And dialysis or transplant can be life-saving when kidney function is very poor. But the treatments doctors can offer are never as good as a normally functioning kidney. And that was what my resident's "secret" really meant.

Two new studies lend more support to the idea that normal kidney function is important for good health. The research was published in the latest issue of the Journal of the American Society of Nephrology. Both studies kept track of kidney function over time among thousands of people. Some had normal kidney function at the start. Others had some degree of kidney disease.

In both groups, declining kidney function was a powerful predictor of future health problems. These included:

• Heart failure (a reduction in the pumping function of the heart)
• Heart attack
• Peripheral artery disease (poor circulation)

People with declining kidney function also were more likely to die early.

Some of the connections between kidney disease and these other health problems are direct and well known. For example, diabetes can damage small blood vessel in the heart and kidney. As a result, kidney damage commonly occurs along with heart and artery disease among people with diabetes. However, the reason that declining kidney function may predict future heart failure is not so clear.

The message I take away from this new research is this: Do what you can to take care of your kidneys. The health of your kidneys could be key to your overall health.

What Changes Can I Make Now?

You can take these measures now to keep your kidneys healthy:

• Keep your blood pressure normal. If you have high blood pressure, diet, exercise, and loss of excess weight can help. However, medicines are often needed. Drugs called ACE inhibitors can particularly help to protect the kidneys for someone who has high blood pressure and kidney disease.



• Control your diabetes. Keeping your blood sugar normal or nearly normal can reduce the chances that diabetes will damage your kidneys



• Take care of your heart and arteries. Reduce high cholesterol, don't smoke, and take medicines as needed to protect your heart and blood vessels. All of these steps can also protect your kidneys.



• Avoid medicines that harm the kidneys. If you have kidney disease, tell any doctor who treats you. This may alter the doctor's choice of treatments. Medicines that can worsen kidney disease include:
  
  • Ibuprofen
  • Related anti-inflammatory medicines
  • Intravenous dye used in certain medical tests


• Adjust your diet. For people with advanced kidney disease, some experts recommend a low protein diet (or at least avoiding a high protein diet). Ask your doctor about this if you have kidney disease.



• See your doctor regularly, especially if you already have kidney disease. Evaluation by a kidney specialist (a nephrologist) can be valuable, especially if your kidney disease is advanced or getting worse.



• Plan ahead. If kidney disease is getting worse over time, plan for dialysis or transplant well in advance. This can avoid complications and emergency treatment.

What Can I Expect Looking to the Future?

You can expect to hear about more research that clarifies how declines in kidney function contribute to early death, heart disease and other problems. These new studies found an association between declining kidney function and serious health problems. But it's not clear that kidney disease caused these problems. We need research to find out whether treatments that protect the kidneys also prolong life and prevent these other diseases.

Many types of kidney disease are not considered preventable. So we badly need better ways to protect kidney function, especially as people live longer. I hope that future research will find new ways to intervene when people experience declines in kidney function.