After My Blood Donation Went Wrong, I Consulted a Cardiologist: Here’s How Runners Can Time Them More Safely
As soon as my appointed nurse pulls the needle out of my vein, I try to sit up to free my spot for the next blood donor. Right away, a hot flush washes over my body, and I immediately fall flat again.
Very calmly, the nurse pulls a bag of ice from a nearby cooler and places it behind my neck, telling me to stay horizontal as long as I need. “Does this happen often?” I ask, closing my eyes to stop the dizziness. He nods and says, “Every so often.” I’m perplexed, as I’ve donated blood before, and while I cannot watch a needle being stuck into my inner elbow, the sensations otherwise don’t bother me; as long as I can keep my head turned the other direction, I’m usually fine.
The moment I finish the snack the nurse handed me to raise my blood sugar, I try to get up again, and the same dizzy spell places my head back on the ice pack. Too soon. Okay, so let’s lie here and contemplate what I did differently this time. A few things come to mind: maybe, despite having breakfast, morning donations are just not my thing, or maybe, coming back eight weeks after my last appointment was too soon. Or maybe I should not donate the day after doing intervals—I’ve only just started my next training block, so I didn’t think much about it.
Although my race will be long over by the time I’m eligible to donate again, I decide then and there to speak to a doctor about when it’s safest for runners to donate blood.
The Basics of Blood Donating
Donating blood is an incredibly rewarding act. One pint of your whole blood can save up to three people. You’re eligible to donate if you’re at least 16 in most states, weigh at least 110 pounds, and are feeling well in the days leading up to your appointment. Before your donation, a nurse will measure your pulse, blood pressure, and hemoglobin levels to ensure your body is ready to part with approximately 10 percent of your blood supply. Under intervals set by the U.S. Food and Drug Administration, it can do so every 56 days or eight weeks, up to six times a year, regardless of gender.
In contrast, many European countries suggest different limits, recommending that men donate up to five and women up to four times a year, drawing 450 milliliters of blood at once, compared to the 500 milliliters in the U.S. that make up a pint. In the Czech Republic, my home country, the recommended max is even lower: four times for men and three times for women, with at least 10 weeks between donations. The limitations have to do with anemia prevention; plus, a woman’s body loses blood during every menstruation and overall has a lower blood volume and iron storage than a man’s.
The Best Time to Donate
Knowing how much running depletes the body, should runners donate as often as people who don’t do aerobic endurance sports?
“It definitely is really different just because we’re already placing demands on our body with respect to how much we actually need iron, how much we rely on oxygen uptake to support our muscles and our vital organs,” says Tamanna Singh, MD, director of the Sports Cardiology Center and cofounder of Women’s Integrated Sports and Exercise Care Center at the Cleveland Clinic. “Some of the literature that I saw with respect to runners suggested [donating] maybe two or three times a year, and that’s probably also going to depend upon what your training cycle looks like.” Female runners in particular tend to have iron deficiency anemia that sometimes goes untreated, either due to underdiagnosis or unawareness.
If you race often, you’re compounding frequent dehydration with loss of iron caused by the breakdown of red blood cells from the physical impact of your feet hitting the ground, which your body is constantly trying to rebuild, and that can turn into a vicious cycle, Singh says. “If you want to donate blood, there are opportunities to do that, like during off-season, but certainly not before a race, during peak training, and I would also recommend against it after racing,” she adds.
Aim for the period between training blocks, when you’re truly just maintaining your base, and within that time, schedule the donation during the days you’re not exercising. “I would not do it on a speed day or the day before a speed day or the day before a long run—keep it away from intensity and volume,” Singh says, explaining that you’re already dehydrated and depleted, so donating blood would make you feel even worse for the next couple of days. “I would do it if you had a couple of rest days, and understand that it’s going to take more than a couple of days for you to replace all of that iron that you lost.”
Once your race is over, Singh offers anecdotal advice for how long to wait: take as long as you do to recover after your race before running again—Runner’s World usually recommends taking as many days off from running as miles you raced.
If you race one marathon a year, you’re likely in off-season for half of the year, which would be a great time to donate, but keep in mind that you won’t be able to perform at your peak fitness. “Those are going to be times where you’re going to probably feel a little bit more fatigued during runs,” Singh says. “If you’re able to amp it up a smidge with iron supplementation, great, but that would not be the time to start doing mega intensive training for a hard race just a couple of weeks later.” If you do two or three marathons a year or race even more frequently, it may be harder to identify a true off-season. “Do it during your fun races, but then support yourself with extra hydration, iron supplementation, staying on top of your ferritin levels,” Singh says.
In my case, I just raced a half marathon, and recovery “can take two weeks, depends upon the intensity,” Singh says. “If you worked hard, it might take you three to four weeks to recover, and that’s a reasonable time to consider donating blood.”
The same rule applies for shorter races as well. “I would argue it really is dependent upon the intensity, volume of your training, and your goals,” Singh says. “If you’re really competitive and work really hard training for a 5K, donating your blood during that time could cause some havoc with respect to your oxygen-carrying capacity, leading to just more fatigue.”
Other Types of Donations
Another way to do some good when whole blood donation doesn’t fit into your schedule is to donate just part of your blood. “With red blood cells, we’re losing 200 to 250 milligrams of iron, and it can take four to eight weeks to replenish that without iron supplementation,” Singh says. “With plasma, because we’re not actually taking any red blood cells out, we’re not depleting iron stores, and so you might feel fatigued immediately after donation, but you really bounce back within two or three days.”
In the end, you have to decide what’s best for you. “It’s a balance, right? If donating is really important to you, do it: it’s fantastic, such a great way to give,” Singh says. “But it’s okay to also have goals in running. Everybody should always have off-season training or base building, and that’s going to be the right time to donate.”
Bottom Line
As a European, I couldn’t donate blood in the U.S. until October 2022 due to restrictions related to Creutzfeldt-Jakob disease, also known as “mad cow disease,” that used to circulate and be feared among Europeans in the ’90s. The risk has been considered low in the last few years, which is why the American Red Cross updated its eligibility rules. When I finally donated my first pint in early 2025, I messaged my dad about it, excited to share my blood group and compare notes. Growing up, he had a wall full of pins in his workshop, multiple rows made of tiny blood drops. I didn’t ask, just assumed they were tied to blood donations.
That’s when I learned that my dad has a fear of needles and would never let anyone stick one in his arm voluntarily. All these pins? They were my grandfather’s; he started donating during his army training in his 20s, and throughout his life, a local hospital would come pick him up from work when they were running short on blood because he was a universal donor. My grandfather passed away in October 2024, and I like to think that he made it somehow happen so I could take over for him. As I lie on the medical bed, squeezing and releasing the soft ball the nurse placed in my injected hand, I think of him; he’s why this is important to me.
After my ice-filled headspin episode, I decided to follow my own schedule based on the European—and the cardiologist’s—recommendations, keeping my donations to three times a year, as opposed to the six the American Red Cross would love me to come in for, spacing them out, and scheduling appointments only in between my training blocks.
Now that my half marathon is over, it’s time for my next one!
Pavlína Černá, an RRCA-certified run coach and cycling enthusiast, has been with Runner’s World, Bicycling, and Popular Mechanics since August 2021. When she doesn’t edit, she writes; when she doesn’t write, she reads or translates. In whatever time she has left, you can find her outside running, riding, or roller-skating to the beat of one of the many audiobooks on her TBL list.