Why do people with CKD have low iron?

Iron deficiency anemia is a common problem for people with CKD or Chronic Kidney Disease. According to one published study, anywhere from 8.4% of people with Stage 1 CKD and 53.4% of people with Stage 5 CKD have anemia. In another study, more than half of the men were found to have low iron and more than two thirds of women were iron deficient.

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The three main causes of low iron for people with CKD are low intake or absorption of iron, blood loss, and use of erythropoietin stimulating agents.

Low intake or absorption of iron in CKD

Low intake of iron in CKD

In order to maintain good iron levels in the body, people need to eat a certain amount of iron each day. If you do not eat enough iron, then you may be come iron deficient.

The recommended daily allowance for adult men and post menopausal women is 8mg of iron per day. For women who are still menstruating, the recommended daily allowance is 18mg of iron per day.

When most people think of high iron foods, they often picture red meat. However, people with chronic kidney disease often cut back on their intake of red meat as well as other animal proteins and begin to focus more on plant based diets due to the many kidney benefits of a lower protein, plant based diet.

Many people assume that a plant-based diet will be low in iron, but that is not necessarily the case. The sample meal plans provided in our courses have an average of over 10mg of iron per day, so for the vast majority of people, a balanced plant-based diet can meet the recommended daily allowance for iron. Nuts, beans, seeds, and legumes are all good sources of plant based iron.

However, a lower protein diet that is high in processed foods or less nutrient dense foods may not provided an adequate amount of iron.

Low absorption of iron in CKD

If you are eating an adequate amount of iron, there may be issues with how well your body absorbs the iron that you are eating. There are several things that can impact how much iron your body absorbs.

Tannins and Iron Absorption

Certain foods and beverages contain other minerals or compounds that can bind with iron and prevent your body from being able to absorb it.

Coffee and tea contain compounds called tannins. Tannins can bind with iron in food and prevent it from being absorbed. If you drink a lot of coffee and/or tea with meals, this can impact how much iron your body is able to absorb.

Similar to tannins, calcium can bind to iron and prevent it from being absorbed by your body. If you eat a lot of dairy foods or foods containing calcium, this can lead to iron deficiency.

Lack of Vitamin C and low iron absorption

Plant foods contain a type of iron called non-heme iron. In order for your body to efficiently absorb this type of iron, there must be some Vitamin C in the same meal.

This is one of the many reasons that it is important to get enough fruits and vegetables in your diet. Fruits and vegetables will be the main source of Vitamin C in your diet, so eating a fruit or vegetable with each meal or snack is going to really improve your absorption of iron.

fruits and vegetables improve iron absorption in CKD

Blood loss and iron deficiency in CKD

Iron is needed to form hemoglobin in your blood, so every red blood cell contains iron. When you lose blood, your body loses iron as well.

Some causes of blood loss are easy to spot:

  • Heavy periods in women who are still menstruating
  • Blood in the urine
  • Frequent cuts or scrapes

Some bleeding is more difficult to assess such as:

  • Frequent lab draws
  • Gastrointestinal bleeding

People with CKD are typically at greater risk for gastrointestinal bleeding for a variety of reasons:

  • Many people with CKD also take anti-coagulant medications which increase your risk of blooding because they increase the amount of time that it takes for blood clots to form.
  • Clotting disfunction due to uremia – when there is a build up of uremic toxins in the blood, it can affect the body’s ability to form blood clots in response to bleeding, which means more blood will be lost
  • Cardiovascular disease – many people with CKD also have some degree of cardiovascular disease which can increase your risk of bleeding
  • Smokers are at increased risk of bleeding
  • Old age is a risk factor for developing gastrointestinal bleeding

If you have diverticular disease, colitis, esophageal varices, hemorrhoids or peptic ulcers, you are at an increased risk of gastrointestinal bleeding that can ultimately lead to iron deficiency.

If your healthcare provider determines that you are iron deficient, determining if there is any unknown bleeding causing the iron deficiency is an important next step to prevent future complications.

Erythropoietin Stimulating Agents and Iron Deficiency in CKD

As kidney function declines, the kidneys stop making an important hormone called erythropoietin.

Erythropoietin is a hormone that helps to stimulate your bone marrow to make more red blood cells. If anemia reaches a certain threshold, your doctor may prescribe a medication to help stimulate red blood cell production. These medications are called erythropoietin stimulating agents (or ESAs for short!).

ESAs can stimulate rapid production of red blood cells. The new red blood cells can quickly use up the available iron in your blood and lead to what is called a “functional iron deficiency”. Your body may still have some iron stored in the liver, but for various reasons, the liver cannot release the iron fast enough to meet the needs of the new red bloods cell, which will lead to iron deficiency.

In this situation, supplemental iron may be needed which your doctor would determine.

How do you know if you have low iron levels?

Some common signs and symptoms of iron deficiency include fatigue, weakness, exercise intolerance, restless leg syndrome, and pica. Pica refers to a desire to eat substances that are not considered food like ice chips, clay or dirt, paper products, corn starch, chalk, etc. If you find yourself craving these things, it’s often a good sign that you may be iron deficient.

If you have any of the symptoms above or risk factors for iron deficiency, then you may want to ask your healthcare provider to check your iron labs.

Typical lab work will often include a Complete Blood Cout, which would include:

  • Red Blood Cell Count
  • Hemoglobin
  • Hematocrit
  • Reticulocyte Count
  • Mean Corpuscular Volume (MCV)
  • Mean Corpuscular Hemoglobin (MCH)

Sometimes it can take awhile for the labs listed above to show signs of iron deficiency. These labs can appear normal even if you have an iron deficiency, so it is important to request additional labs to assess iron status such as:

  • Serum iron
  • Serum ferritin
  • Total Iron Binding Capacity (TIBC)
  • Transferrin Saturation (TSAT)
  • Reticulocyte hemoglobin content (CHr)

With some these labs, your healthcare provide can determine if there is an iron deficiency or rule out an iron deficiency if you have symptoms that could be caused by another issue.

If it is determined that you need to take a supplement, your healthcare provider will help you determine the appropriate dosing. Too much iron can be toxic, so it is important to supplement with iron under the supervision and guidance of a healthcare provider.

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