Why are Kidneys Important?

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Could you answer if someone asked you, “why are kidneys important?” When we think about chronic kidney disease, we usually think about the changes in the diet, medications, and yes, dialysis. However, to better understand why such changes are encouraged, it’s helpful to understand exactly why kidneys are important.

About the Kidney

The kidney is a bean-shaped organ. It’s about the size of a fist and located in the torso. They are located towards the lower back. 

Most people have two kidneys. However, some are born with one that just does the job for two. Also, many choose to be living donors.

People with one kidney can live healthy normal lives. In many cases, there are no special dietary needs for a single kidney. A healthy, balanced diet and proper hydration will help protect that solo kidney.

Filtration System

The nephrons are the filtering units within the kidneys. The glomerulus, on the other hand, is a bunch of tiny blood vessels. This is where the filtering process happens.

The kidney filters blood non-stop. About a half cup of blood every minute. In a full 24 hours, the kidneys filter about 180 liters of blood.

The kidneys pull extra fluids, toxins and waste products from our blood. This is how urine is formed. Larger items like protein and red blood cells pass through. They are kept in the body.

That being said, the kidneys even filter vitamins and minerals. This includes B-vitamins, sodium, potassium, and phosphorus. Excess is filtered out in the urine.

In the renal function panel, the glomerular filtration rate, or GFR, measures kidney filtering. Generally, a GFR of more than 90 is normal.

However, kidney hyperfiltration is a filtration rate above normal. More importantly, it is considered a risk factor for heart disease and death. A diet high in protein can lead to hyperfiltration. It can also cause kidney damage. Therefore, a low protein diet may be advised for kidney disease.

With Chronic Kidney Disease

With kidney disease, risk of nutrient, toxin, and waste build up is higher. More specifically, damage to kidneys can lead to damage of the filtering process. Consequently, larger items like protein leak into the urine.

This is where specific diets are important. More specifically, the different stages can result in different diet, medication, and lifestyle needs for each person.

Taking kidney “cleansing” vitamins are not helpful. When the kidneys aren’t working, they won’t get rid of the excess.

Balancing pH

The body’s functions need a specific pH balance to perform jobs. More specifically, the lungs help get rid of too much carbon dioxide in our breathing. The kidneys help get rid of too much acid and base.

The kidneys filter excessive acid. This makes sure your blood and body is balanced at just the right pH. Balance is measured in the serum bicarbonate levels. Find this in the renal function panel. Normal range is between 22-29 mEq/L.

Another important factor is stopping kidney stones from forming. Kidney stones are formed in an acidic environment. Therefore, acid-base that is not quite right in our body can increase the risk of kidney stones.

With Chronic Kidney Disease

The body becomes more acidic with kidney disease. About 15 to 19% of people with chronic kidney disease also have metabolic acidosis. More specifically, this is when serum bicarbonate levels fall below 22 mEq/L.

Metabolic acidosis can cause major problems, including osteoporosis and worsening CKD. Even vitamin D levels can be changed with metabolic acidosis.

Medication like sodium bicarbonate or sodium citrate are often prescribed to make sure the balance is kept. To note, it’s important to take medications as directed. Do not take medications or baking soda without your doctor telling you to. You could develop metabolic alkalosis.

On the other hand, if you are on dialysis your dialysate includes bicarbonate. This is to help keep balance. Most do not take medications as the dialysate is changed to meet bicarbonate needs.

That being said, the diet plays a big role in stopping metabolic acidosis. Knowing the potential renal acid load in your diet helps. Lowering acid load in the diet can decrease sodium bicarbonate prescriptions.

Red Blood Cells

Red blood cells help bring oxygen and nutrients to the organs in the body. Oxygen is needed to keep all organs working. The kidney cannot perform all of these important jobs if it does not get enough oxygen.

Erythropoietin

Another very important hormone, erythropoietin (aka EPO) is made in the kidneys. To clarify, EPO is the hormone that creates red blood cells.

With Chronic Kidney Disease

One of the first symptoms felt with kidney disease is fatigue and low energy. Low hemoglobin, or anemia, is often the cause. Symptoms of anemia include low energy/fatigue. It can also include looking pale, cold hands or feet, poor appetite, or problems concentrating. 

When there is not enough erythropoietin in the body, a doctor may start iron therapy. Treatment is iron supplements by mouth or intravenous iron therapy. These therapies use an ESA, or erythropoiesis stimulating agents.

However, you can also make changes to your diet to stop anemia from worsening.

Bone Health

The kidneys help keep the bones strong. For example, they balance nutrients like calcium and phosphorus. Both of these are kept mostly in the bones.

Phosphorus and Calcium Balance

The kidney gets rid of both phosphorus and calcium when there is too much. The parathyroid glands help balance calcium and phosphorus.

The parathyroid glands release parathyroid hormone (or PTH). PTH helps with the balance of calcium.

Vitamin D

Vitamin D, a fat-soluble vitamin, is not made by kidneys. Rather, the kidney activates vitamin D.

Vitamin D is synthesized in the skin from near-UV light. We can get the precursor of vitamin D3 from animal foods. D2, on the other hand, comes from plant sources. The liver then makes it into 25(OH)D3. Finally, the kidneys then make that form of vitamin D to 1,25(OH)2D3. This is the active form of vitamin D.

Here’s a video about vitamin D.

With Chronic Kidney Disease

Secondary hyperparathyroidism is very common with CKD. To clarify, this is when enlarged parathyroid glands release too much PTH. This then pulls out too much calcium from the bones. Phosphorus then follows. 

High phosphorus levels can also lead to more PTH. This is why it’s important to limit how much phosphorus you eat. In particular, limiting phosphate additives.

Too much phosphorus or calcium in the blood can lead to vascular calcification. This is otherwise known as hardening of the arteries.

Vitamin D deficiency is very common in those with kidney disease. Importantly, lower vitamin D levels can lead to problems like osteoporosis or secondary hyperparathyroidism. Even balance issues can happen with untreated low vitamin D.

Vitamin D supplements are often recommended in those with kidney disease. Research has shown vitamin D3 is more effective than D2, especially when paired with vitamin K2.

Blood Pressure and Hydration

As mentioned, the kidney gets rid of excess water. This helps to keep our hydration level balanced. However, the kidneys can hold on to water to stop low blood pressure.

The kidney decides how much fluid we need. Urine production is based on excess fluids. Therefore, changes in blood pressure can lead to more or less urine production. 

Renin-Angiotensin Aldosterone System

The renin-angiotensin aldosterone system (or RAAS) is the system set in place to help manage blood pressure and blood volume.

Renin is an enzyme released from the kidneys. This helps increase blood pressure when it’s too low. The kidneys also work to hold onto sodium and fluids to help increase blood pressure.

With Chronic Kidney Disease

ACE-inhibitors are often given to those with kidney disease. This is to stop blood pressure increase. In turn, blood pressure is kept lower.

Some people with kidney disease need to limit their fluids. Some need medication to help with going to the bathroom. Similarly, the ability to urinate can decrease as kidney function decreases. Therefore, many with later-stage kidney disease need medications. They also may need a fluid limit to prevent high blood pressure and fluid overload.

So why are kidneys important?

As we’ve seen, the kidney clearly has very important jobs in the body. Some of these functions can decline with or without symptoms in kidney disease.

If you have kidney disease, you may need help with changes in medical care, medications, diet, and lifestyle. Talk with your healthcare team about what you can do – as a team– to keep your kidneys working.

Struggling with kidney disease? Want to learn more about the kidney diet and kidney-friendly nutrition? Check out our Plant-Powered Kidneys online course!