Hello. Join Utahrunning.com, it’s FREE | Sign in | Sign in

Your Run Starts Here!

Feeling Overly Fatigued When Running? Low Iron or Vitamin D May Be The Culprit.

by Jason Blackham


Do you have excessive fatigue with your running? If you do, you should consider seeing a physician to have blood work done.  The most common causes of fatigue in athletes is poor nutrition, sleep problems, underlying medical problems, iron deficiency, and Vitamin D deficiency.  When seeing patients experiencing fatigue, I usually check a panel of labs to look for underlying causes as well. In this article, I will address iron deficiency and Vitamin D deficiency.  

Low Iron Levels

One of the most common underlying reasons for fatigue in athletes is low iron levels.  When iron levels are low for long enough, anemia or low red blood cell counts result.  However, one can be iron deficient without having anemia.  Anemia is most common in women athletes during the ages of menstruation due to loss of blood with menstrual cycles combined with not having enough iron in the diet.  Other major causes include bleeding usually in the GI tract, stomach or bowel, and not enough iron in the diet as well as other medical problems.  

Decreased iron or ferritin levels can cause fatigue, decreased performance, and lower red blood cell mass.  When one goes to higher altitudes for prolonged times, the red blood cell mass increases due to a response to lower oxygen levels.  However, if iron stores are low, then the body can’t adapt by increasing red blood cells.  Therefore, one doesn’t have the training response with altitude.  

In order to see if one is deficient in iron, your doctor may check with blood work or labs, a CBC or complete blood count, iron level, ferritin level and iron binding saturations.  If one is low in iron, then the other labs help to determine the cause and type of iron deficiency.  Many times the blood counts are normal and the iron is normal as well, however, the ferritin is low.  Ferritin is a marker for total iron body stores which includes muscle and liver stores.  Generally, labs use a ferritin value of less than 20 or sometimes 10 depending on the lab for a low level.  However, my recommendation is a level of 40, which is routine in the athletic population.  If the ferritin is less than 40, then I recommend iron supplementation.  

Iron Supplementation

The best way to supplement iron is with ferrous sulfate which is better absorbed.  A 325 mg tablet has equivalent to 65mg of absorbable iron.  Other formulations of iron have different values of absorbable iron.  It is better absorbed if taken on an empty stomach and with Vitamin C as Vitamin C increases absorption in the stomach and upper gut.  How many times a day to take it depends on the lab results and normalization, then I will change the iron dosage to stabilize the ferritin level.  Some possible side effects include upset stomach or nausea which usually decreases the longer you take it.  Taking it with food usually helps the upset stomach but it isn’t as well absorbed.  Another side effect is green or dark stools.  

A common question people ask me is about iron supplementation that is received intravenously to quickly raise blood levels.  IV iron has been popularized by studies in triathletes in Australia.  I don’t recommend it for several reasons.  First, studies show that taking iron by mouth in a tablet form is just as effective as taking it by IV, and more importantly, that oral intake lasts longer than IV.  

Second, IV iron has major side effects including anaphylactic shock, heart attacks, arrhythmias, infections, and kidney failure in older formulations.  Recent studies show a 2-10% risk.  Other reactions are vein reactions, skin reactions, headaches and muscle aches.  Most people will have to take steroids and Benadryl to avoid it.  IV saline solution has to be given as well to avoid kidney problems which may negate the desired effects in athletes.  

Third, it is considered doping especially if iron levels or red blood cell levels are too high especially when given with IV fluids.  I recommend only using it if an oral tablet isn’t tolerated, if there’s lack of response to oral tablet, or if there’s a medical problem causing malabsorption.  

Low Iron and Ferritin Levels in Women

Maintaining adequate iron and ferritin levels is important. In women, low iron levels or anemia can result in what is called the female athletic triad which is poor nutrition causing anemia, loss of normal periods and stress fractures and/or low bone density.  It results from a balance of high nutritional needs from sports where calories taken into the body are less than calories burned.  The main problem is decreased estrogen levels leading to loss of periods or irregular periods for 3 months, and low bone density.  Therefore, women athletes, especially endurance athletes who have anemia and irregular periods or loss of periods, should be evaluated and may need to see a nutritionist.  It has been shown that fixing the caloric deficits through a nutritionist is effective in fixing the problem and avoids long term problems.  

Considering all the reasons why normal iron and ferritin levels are important, why not just take an iron tablet instead of having labs checked?  This leads to another caution I have. Taking too much iron, or iron overload has negative effects as well.  It can cause problems with joints, dark skin, liver damage, diabetes and other things.  Therefore, it is important to check levels.  

Low Vitamin D Levels

Another common cause of fatigue is low Vitamin D level.  Vitamin D deficiency causes muscle aches and soreness, decreased recovery from work outs, fatigue, depressive symptoms, bone problems, specifically low bone density, which can lead to stress fractures.  Vitamin D binds to calcium in our gut and allows us to absorb calcium.  Our skin makes vitamin D by the sunlight.  Many runners who aren’t in the sun by running in the early morning to avoid the heat are at risk.  However, I am surprised how many runners I see that run in the afternoon, such as collegiate athletes, that have low Vitamin D levels.  It is a common problem and can lead to bone problems as well as fatigue.  

Depending on the person’s symptoms, I generally recommend a level above 40.  If someone is low, especially below 30, I prescribe Ergocalciferol, which is a prescription Vitamin D that is better absorbed, 50,000 units once a week.  To put it in perspective, the normal recommended daily intake is 800 units a day.  I prescribe it weekly for 3 months then recheck levels and if there wasn’t a good response then I double the dose and do another 3 months.  Using an over the counter vitamin D may take a year or more to achieve the same blood levels.  After normal levels are achieved, then I will use 1000 to 2000 units of Vitamin D over the counter or by prescription.  

Too much Vitamin D is not a good thing either as it can lead to bone pain, and too high of calcium in the blood which leads to a host of other problems.  

If you’re feeling fatigued in your distance training, consider the information above and also making an appointment with a physician to check out your levels.


Jason Blackham – MD, Sports Medicine, Competitive Runner


Jason Blackham, MD, Internal Medicine Sports Medicine specialist ran cross country and track for Mountain View High in Orem, Ut, where he was All-State, and for Southern Utah University. He continues to run marathons and road races. He was a team physician for University of Iowa before moving to Ogden at Intermountain Sports Medicine at McKay Dee Hospital, Calton-Harrison clinic.

He is a team physician for area high schools, marathon and other race events, Snowbasin Clinic, and Weber State teams. He has given talks at national sports medicine meetings and running symposiums as well as written book chapters on stress fractures, shin splints and calf muscle strains. He practices non-surgical sports medicine. He treats bone, joint, muscle and tendon injuries and medical issues related to sports with emphasis on running injuries, endurance medicine and medical problems with sports participation. He specializes in overuse injuries and prevention of running related injuries as well as ultrasound guided procedures.

He also specializes in sports related medical problems such as exercise induced asthma, concussion, heart issues, diabetes in athletes, and more. He knows how to keep runners training while rehabbing injuries.

This is one of several great articles from Run Utah Magazines Summer 2017 edition. Check out our other great articles below.

The Top Ten Voted Trails in Utah

Summer is the perfect time of year to get out the door and run. Trail running is a favorite in Utah due to Utah’s incredible scenery and well maintained back country trails. With the vast number of trails throughout the state many runners find themselves constantly exploring new places to run trying to find the perfect trail. If you fit this description look no further…  READ MORE

Successfully Transition From Road Marathon To Trail Ultra

For many road runners finishing a marathon is the ultimate accomplishment. It can take months or years of dedicated training, sacrifice, and dietary discipline to reach the holy grail of 26.2. This is a big deal! You should be proud of yourself for finishing this daunting physical and mental event, right? Of course you should, but it’s likely you are already looking for another marathon so you can improve your time or you have a wall full of marathon medals…  READ MORE 

Hayden Hawks Interview: The Life of an Elite Ultra Marathoner

Hayden Hawks was an elite collegiate athlete that graduated from Southern Utah University. While in School he specialized in the 5k and 10k, running 13:51 and 28:53 for those events. He still lives in Southern Utah and trains as a professional ultra marathoner…  READ MORE

Google Buzz

This entry was posted on Thursday, June 1st, 2017 at 2:16 pm and is filed under Nutrition, Run Utah Magazine, Summer 2017 Edition, Utah Running. You can follow any responses to this entry through the RSS 2.0 feed.

Leave a Reply

Your email address will not be published. Required fields are marked *

Get Instant Online Access to the Latest Issue of Run Utah Magazine!!!
Plus Receive Weekly
Email Updates
of all
the Upcoming Running
Races in Utah.
Enter your Name and Email
below to receive your
FREE subscription:

We respect your privacy.
We will never share, sell or rent your details.

Privacy Verified
  • Featured Partners

  • Let’s Get Social!

    RSS   Twitter   Facebook

    SocialTwist Tell-a-Friend
  • Categories

  • Utah Running Recent Posts

  • UtahRunning.com on Facebook

  • Utah Running Tag Cloud