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Take-home Message: This article supports the idea that taking an iron supplement can improve the athletic performance of women who are iron-deficient.
Women of reproductive age are at a high risk of iron deficiency due to menstruation. In female athletes, the risk is even higher due to factors such as low-iron diets and low levels of inflammation caused by endurance exercise. When severe enough, iron deficiency can lead to anemia (low concentrations of hemoglobin in the blood). Hemoglobin is the protein in your blood that carries oxygen to the rest of your body, including your muscles during physical exertion. Oxygen is important for muscles because it is used during aerobic (literally meaning, “with oxygen”) metabolism, which produces the energy required for your muscles to contract. A key component of hemoglobin is iron; therefore, if you are deficient in iron, your blood cannot carry as much oxygen and your physical performance may suffer.
At least, that has been the theory of exercise scientists. Until now, however, there have been few studies that have demonstrated this relationship clearly. This article in the Journal of Nutrition, however, is a meta-analysis of 22 smaller studies. That means that it pooled the data from smaller clinical trials. This procedure can be useful because the larger the number of patients included, the more power you have to detect a small difference between experimental and control groups.
When data from the smaller studies were pooled, the researchers found that an oral iron supplement improved both maximal and submaximal exercise performance in the women participants. Maximal, or peak, exercise performance was measured by VO2 max, which is the highest rate at which your body can consume oxygen. Everyone has a different VO2 max, which is influenced by things like genetics and training. Imagine running on a treadmill at a sprint until you reach exhaustion – by the end, you’ll be using oxygen as fast as your body possibly can and you’ll be at your VO2 max. In general, the higher your VO2 max, the longer you can run on that treadmill before you become exhausted. The VO2 max of women given iron supplements was on average higher than that of women not on supplements, suggesting that iron improved their maximal, or peak, performance. The amount that VO2 max increased by is about the same amount that training can improve your VO2 max by, which is a fairly substantial effect. At submaximal exercise (meaning exercise at an intensity that is not going to exhaust you), iron supplementation also lowered the heart rate of the women, suggesting that they were performing better at lower intensities as well.
Importantly, these effects were mainly seen only in women known to be iron-deficient or trained athletes (who are at a greater risk for iron deficiency). So this doesn’t mean that every woman should start taking an iron supplement. It does mean, however, that if you are a woman of reproductive age, and especially if you are an athlete, it might be a good idea to talk to your doctor about checking your iron levels. If you are found to be iron deficient, an iron supplement might very well improve your athletic performance significantly.