The big five for endurance athletes

The big five for endurance athletes: iron, vitamin D, magnesium, vitamin B12, and zinc.

Iron — elevated heart rate at easy paces, fatigue that won’t lift with a rest day, breathlessness on hills you used to handle, fitness plateauing despite consistent training. Fifteen to thirty-five percent of male endurance athletes and up to half of female ones show some level of it.

Vitamin D — frequent illness during heavy training, stress fractures or bone pain, muscle weakness, low mood. Up to thirty-nine percent of elite athletes are insufficient.

Magnesium — muscle cramps in calves or feet, eye twitches, poor sleep, suppressed HRV that doesn’t recover with rest, low-grade fatigue. Athletes need about twenty percent more than sedentary people because of sweat loss and muscle repair.

Vitamin B12 — fatigue, reduced exercise capacity, numbness or tingling in limbs, mood changes. Especially relevant if you’re vegetarian or vegan.

Zinc — frequent colds, fatigue, low appetite, slower recovery. Endurance athletes on high-carb, low-protein diets often run low.

The tell across all of them: symptoms that look like overtraining but don’t resolve with rest. That’s when you test, not guess.