Iron

Iron is a mineral central to oxygen transport — it is the core of hemoglobin (red blood cells) and myoglobin (muscle) — and to energy-producing enzymes. Inadequate iron causes iron-deficiency anemia, marked by fatigue, reduced work capacity, and impaired endurance and VO2max (see vo2max-intervals). It is the most common nutrient deficiency worldwide.

Dietary iron comes in two forms: heme iron (animal foods — meat, poultry, fish), which is well absorbed, and non-heme iron (plants — legumes, fortified grains, spinach), which is less bioavailable. Vitamin C consumed with non-heme sources improves absorption, while tea, coffee, and high calcium loads reduce it.

Recommended intake (RDA): 8 mg/day for adult men and post-menopausal women; 18 mg/day for women aged 19–50 (to offset menstrual losses); 27 mg/day during pregnancy. The tolerable upper limit is 45 mg/day.

At-risk groups: menstruating women, pregnant people (see prenatal-postpartum), endurance athletes (losses via sweat, foot-strike hemolysis, and GI losses), and vegetarians/vegans relying on non-heme iron (see plant-based-diet). Iron should be supplemented only when deficiency is confirmed, because iron overload is harmful and the body has no efficient way to excrete excess.

• Core of hemoglobin/myoglobin; deficiency = anemia, impaired endurance/VO2max.
• Heme iron (animal) absorbed well; non-heme (plant) less so — vitamin C aids it.
• RDA: 8 mg/day men & postmenopausal women; 18 mg/day women 19–50; 27 mg/day pregnancy; UL 45 mg/day.
• At-risk: menstruating women, pregnancy, endurance athletes, vegetarians/vegans.
• Supplement only when deficiency is confirmed (overload is harmful).

• minerals-overview — iron among the key minerals.
• plant-based-diet — non-heme iron bioavailability.
• prenatal-postpartum — elevated iron needs in pregnancy.
• vo2max-intervals — iron status affects aerobic capacity.