Ask Pete: How Does Blood Donation Affect Running?

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Question:

After donating a double unit of red blood cells, my running speed and endurance dropped off and I was diagnosed with anemia. Does regular blood donation typically affect running? – Charles

Answer:

While blood plasma (the liquid portion of blood) can recover post-donation in a day, red blood cells require weeks—even months—to return to their previous volume, leading to a period of reduced endurance and performance, as well as to an increased risk of anemia.

A few years back, a high school cross country coach called me in a panic. “We have league finals today,” he said, “and Sarah, my top runner, gave blood this morning! What should I do?” I told him to hold Sarah out of the meet and to remind his athletes that blood donation is an off-season activity. He decided to run her, anyway. She fainted a mile into her warmup.

There’s no question that blood donation is a noble and generous act, especially during times when blood banks run low, as is currently the case due to COVID-19. But that doesn’t negate the adverse effects that depleted red blood cell (RBC) volume will have on your running.

Let’s start by looking at your blood itself. Your blood is composed of about 55 percent plasma, 40-45 percent RBCs, and the rest split between white blood cells and platelets. We’ll focus on plasma and RBCs.

Plasma is the liquid portion of your blood. Training, especially in the heat, increases your plasma volume, a process that begins within hours of your very first run. This is a good thing, because more plasma leads to reduced blood viscosity (resistance)—blood flows more smoothly through your blood vessels. After blood donation, plasma volume returns to normal within about 24 hours.

RBCs carry oxygen from your lungs to your muscles. They also transport carbon dioxide away from muscle fibers. Unlike plasma, an increase in RBC volume requires weeks—sometimes months—of training. Similarly, it can take weeks to rebuild your RBC count after blood donation. How many weeks depends on the type of donation.

There are four types of blood donation. In order, from the type with the least effect on your running to the one with the most:

1. Platelets: After a pint of blood is drawn, the platelets are separated, and the rest of your blood is returned to you. You can donate every seven days.
2. Plasma: After a pint of blood is drawn, the plasma is separated, and the rest (mixed with saline) is returned to you. You can donate every 28 days.
3. Whole blood: A pint of blood is drawn, and none is returned (you lose a pint of plasma, RBCs, platelets, and all). You can donate every 56 days.
4. RBCs: An automated process separates two units of RBCs (versus the single unit harvested in whole blood donation), and the plasma and platelets are returned to you. You can donate every 112 days.

Men and women who donate two units of RBCs must meet a weight standard that roughly translates to a minimum full-body blood volume of 10 pints. So while a donated pint of whole blood results in up to a 10 percent reduction in total RBCs, a two-RBC-unit donation can result in a 20 percent reduction.

What exactly does this mean for you?

Multiple studies have shown decreases in VO2max of between 4-11 percent after blood donation of a single unit of RBCs. Lower VO2max means less oxygen to your muscles, which results in less energy for your muscles to perform. Less energy leads to slower running speed, reduced endurance, and a greater reliance on anaerobic energy—a 2008 study found that a runner’s anaerobic threshold (the point at which running become noticeably more anaerobic) drops from about 80% VO2max (normally tempo pace) to 70% VO2max (normally distance-run pace). Donate two units of RBCs, and those negative effects are multiplied.

Furthermore, a 2016 study on runners who donate blood regularly cited three areas of concern:

• Maximal power output and VO2max were decreased for up to four weeks after a single donation.
• Beneficial training adaptations were hindered by repeated donations (separated by three months).
• Oxygen transport was lowered by a single donation, then lowered even more following repeated donations (again, separated by three months).

The National Institute of Health has also warned that “25-35 percent of regular donors develop iron deficiency. Since iron is needed for red blood cell production, low iron can cause fatigue and anemia.”

Being a good person sometimes comes at a cost. A runner who donates blood will need at least three weeks to fully recover—more for a two-unit RBC donation, and even more for repeat donations. My advice is to compromise: Save blood donation for the off season, consider iron supplements after two-unit donations, and allow yourself a slow road to recovery while you rebuild your RBCs.

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Pete Magill is a running coach, world-class runner, and author. As a coach, Magill has led his masters clubs to 19 USATF National Masters Championships in cross country and road racing and has worked with athletes of all ages and abilities. He holds multiple American and world age-group records and is a 5-time USA Masters Cross Country Runner of the Year. Magill is author of Fast 5K, SpeedRunner, Build Your Running Body, and The Born Again Runner.