Many older men have low-normal kidney function, but it doesn't need to become a serious health threat.
Chronic kidney disease means the kidneys—the body's blood-filtering urine factory—have less capacity to filter
toxins from the blood and excrete them in the urine. Half of U.S. adults over 75 may have below-normal kidney
function, but most of them will never get sick from it. In men whose kidney function is falling, certain steps
can help to slow or prevent further losses.
"Kidney function appears to decline with age in some people, but it does not necessarily cause a problem unless
you have other health conditions," says Dr. Melanie Hoenig, an assistant professor of medicine at
Harvard-affiliated Joslin Diabetes Center.
What causes it?
Every day, a healthy kidney filters a total of about 200 quarts of blood, removing waste products, excess water,
and certain chemicals. If the kidneys didn't keep things in balance, you would slowly poison yourself.
The kidneys have a remarkable ability to keep working despite changing conditions, like drops in blood pressure.
The tiny filtering tubes in the kidney, called glomeruli, adapt in various ways.
In a serious health crisis, the kidneys may shut down completely as a defensive move to keep fluids in the body.
That's called an acute kidney injury, and it happens frequently to people who are hospitalized.
Smoking, excessive alcohol consumption, high blood pressure, and high blood sugar (diabetes) all harm the kidneys
and can lead to chronic kidney disease. If you are leading a heart-healthy lifestyle (regular exercise and a
nutritious plant-based diet), that will help protect your kidneys.
How low is low?
A healthy kidney filters wastes from the blood at a rate of 90 milliliters (ml) per minute or more. This is known
as the glomerular filtration rate, or GFR. With time, many men's kidneys start to slip, but function must
decline quite a lot before you start to really feel the impact. "You feel fine up to the point that kidney
function is almost gone, which means you can lead a normal life with reduced kidney function," Dr. Hoenig says.
On the other hand, lack of early warning from symptoms can deny you the chance to slow the slide. "Most people
don't start feeling really ill until kidney function is under 10%," Dr. Hoenig says.
How is it tested?
As part of standard blood tests, your doctor may check the level of a protein called creatinine. This provides a
way to assess kidney function.
Creatinine is one of the things that the kidneys filter from the blood. If the kidneys start to fail, creatinine
rises. The creatinine level is used to calculate an estimate of the GFR and provide an estimate of your kidney
function. It is often just an estimate because the formulas doctors use are not accurate when the kidney
function is close to normal.
At different levels of kidney function, individuals tend to have similar problems. But once a person reaches a
certain stage of reduced kidney function, he may be stable and never progress to the next stage. If the function
is low but stable, you may not need to see a doctor about it—providing you are leading a healthy life and doing
well. "If the GFR is declining and already under 50, I think it would be a good idea to see a kidney doctor, if
for no other reason than to become educated," Dr. Hoenig says.
How high blood pressure damages the kidneys
High blood pressure can cause tiny cracks in the lining of arteries, which provide a breeding
ground for fatty deposits that hamper blood flow. As the arteries that feed blood to the kidneys
narrow, the body produces renin, a hormone that makes small arteries narrow further. This
worsens high blood pressure, causing even more kidney damage. Over time, restricted blood flow
can damage or destroy the nephrons, the tiny filtering units inside your kidneys.
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Protecting your kidneys
If kidney function begins to slide, men are not powerless against it. Here are some steps you can take:
Keep your blood pressure and blood sugar within norms. This will help slow the decline
in kidney function. Especially, keep blood pressure below 130/80.
Lower your cholesterol. Taking a statin medication to lower "bad" LDL cholesterol may
help to protect the kidneys. Also, individuals with reduced kidney function are at greater risk for
cardiovascular disease, so reducing cardiac risk factors is important.
Consider medication. Certain prescription medications can protect the kidneys. The two
that physicians often use for this purpose are ACE inhibitors (also commonly prescribed for high blood pressure)
and angiotensin-receptor blockers (ARBs). These or other drugs can lower pressure in the kidney filters and
limit further damage.
Limit protein intake. Eating too much protein can strain weak kidneys. Limit your
protein intake every day to no more than 1 gram per kilogram (2.2 pounds) of body weight. Consulting with a
dietitian can help you plan meals that are safe for weak kidneys.
Use NSAIDs with caution. Nonsteroidal anti-inflammatory drugs (NSAIDs), such as
ibuprofen and naproxen, interfere with kidney function. Taking them when you are also depleted of fluids can
lead to kidney shutdown and possibly hospitalization. Drink plenty of water when you are using NSAIDs. As kidney
function declines, doses of other medication may need to be reduced to prevent kidney damage, including
antibiotics, diabetes drugs, and some heart medications.
