It’s not unusual to feel fatigued during a workout (‘work’ is in the name, after all). However, there’s an important difference between a workout that makes you a little tired and one that leaves you extremely fatigued --- a feeling that can linger the rest of the day. The latter may be caused by something called exercise-induced anemia. Exercise-induced anemia happens when someone isn’t storing or absorbing iron properly, which results in a low red blood cell count. If you have exercise-induced anemia, you’re likely to feel lightheaded or dizzy, fatigued, and may find yourself short of breath when you exercise.

Here’s a look at exactly how your workout can influence your iron levels. Read on to understand the connection between which types of exercise affect iron absorption and storage and what you can do to prevent exercise-induced anemia.

What you should know about exercise-induced anemia

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Lifting weights can impact iron levels

Strength training with weights has tons of health benefits, including weight loss and maintenance, and protecting your joints from injury. But those who follow a more intense weight lifting routine may need to closely monitor their iron levels. Research published in Medicine & Science in Sports & Exercise looked at 40 college students participating in a 12-week weight training program. All of the subjects did not have prior weight lifting experience. While the participants in the study increased their strength and lost body fat after 12 weeks, hemoglobin concentration decreased. Hemoglobin is a protein found in red blood cells that carries oxygen throughout the body. Hemoglobin is produced by iron, and having low amounts of hemoglobin can result in anemia.

The study further showed that total iron intake declined after 12 weeks, particularly in men that had baseline average iron levels. The male subjects had low serum ferritin levels, a blood protein that contains iron.

To be clear: The research doesn’t mean that lifting weights can’t be a part of your routine; in fact, there are many benefits of strength training. It just means that if you start a new weight lifting routine or increase your existing one, it’s important to keep tabs on your iron levels. You can visit your doctor and request the labs you need, or explore at-home lab testing kits like the ones offered by Base.

Cardio may crush your iron levels, too

Whether you run, cycle, swim, or do any other type of aerobic exercise, doing so at an intense level can take a toll on the iron levels in your body. This typically takes a lot more than 30 minutes on the treadmill or elliptical. Iron levels tend to dip in athletes that are endurance training (think: marathon or half-marathon distances) or do continuous, strenuous training, despite having a race lined up or not.

Research published in The FASEB Journal found that regular aerobic training can reduce the efficacy of iron supplementation in females, meaning that even those who take iron supplements are still at-risk for exercise-induced anemia if they do consistent cardio.

Iron loss and lack of absorption can happen for several reasons. First, intense exercise like middle and long-distance running can cause hemolysis, the destruction of red blood cells. Without enough iron to make new red blood cells, oxygen can’t circulate throughout the body and symptoms like fatigue follow. When you exercise you also sweat, and the more you sweat the more iron that gets secreted with it, contributing to iron loss.

Pre-menopausal women, in particular, may be at a higher risk of exercise-induced anemia due to monthly menstrual bleeding, which sheds iron in the process. This in addition to strenuous exercise increases the amount of iron lost. A study published in JAMA estimates that while the general population has a prevalence rate for iron deficiency of 2%, in women that jumps to over 5% due to these factors.

Warning signs your workout is affecting your iron levels

There are some red flags to look out for, such as:

  • Constant fatigue

  • Exercise intolerance, meaning you can’t finish or sustain your normal effort during a workout

  • Muscle weakness

  • Persistent headaches

  • Irritability and mood swings

These signs could point to low iron levels or exercise-induced anemia. The best way to actually confirm that your iron levels are low? Of course, it’s checking them. You can do this via blood samples through a health care provider or check them at home with Base.

When it’s your workout that is causing your fatigue, the fix can be relatively simple. Easing up on the intensity of your workout, whether it’s from lifting weights, cardio, or both will restore iron levels in the body. This happens because decreasing your activity levels will simultaneously reduce how much you’re sweating and the amount of iron you are excreting. Red blood cells can also be destroyed during exercise, meaning there is less hemoglobin delivering oxygen around the body. Be aware that this won’t happen overnight, it can take several months to see improvement. In the meantime, taking iron supplements in addition to focusing on less strenuous exercise can help.

Not everyone is in a position to change their workout routines, however. For example, athletes or those who do high amounts of manual labor on a daily basis, will need to take another path to managing their levels and that’s where iron supplements come in. This is quite common, actually, as an estimated 28% of female marathon runners have an iron deficiency, and 10 to 15% of all athletes deal with mild forms of exercise-induced anemia.

In some cases, iron supplements don’t provide enough of a boost, and in those cases, it’s best to see a health care provider to rule out an underlying condition that may be contributing to low levels of iron, such as an infection or gastrointestinal disease. By regularly monitoring your levels (approximately every three months) you can have constant insight into whether your change in routine is balancing your iron levels to reduce symptoms, or if more extensive care and treatment is needed.


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