Donating blood affects fitness

Holidays mean blood drives, but rolling up your sleeves can interfere with your training.

Each time you donate, you part with about nine or 10 percent of the 5.5 liters of blood coursing through your veins, says Brett Dolezal, Ph.D., associate director of the Exercise Physiology Research Laboratory at the University of California, Los Angeles. You lose red and white blood cells as well as plasma, the clear part of blood that’s left over after all the other components are removed. That’s no big deal—your plasma levels return to normal within 24 to 48 hours, explains Equinox Health Advisory Board member Brandon Marcello, Ph.D., a high-performance strategist in Sarasota, Florida.

From a fitness perspective, you should be more concerned about the fact that giving blood means losing hemoglobin, a protein within red blood cells that carries oxygen through your body, he explains.

As a result, your VO2 max will be about 10 percent lower than average for anywhere from four to eight weeks after giving blood, possibly even lower if you’re at high altitudes. This means you’ll feel more winded than normal during your workouts, fatigue could linger for longer periods of time, and you won’t feel quite as prepared to train again the next day.

Still, none of this means you shouldn’t give, it’s just about timing. Here, six guidelines to follow so you can save lives without sacrificing fitness.