A systematic review in the Journal of Nutrition has associated iron supplements with improved exercise performance of women in child-bearing years.

Lead researcher, Dr Sant-Rayn Pasricha from the University of Melbourne School of Population and Global Health and colleagues concluded that iron supplementation improved women’s exercise performance, in terms of both the highest level they could achieve at 100% exertion (maximal capacity) and their exercise efficiency at a submaximal exertion. Women who were given iron were able to perform a given exercise using a lower heart rate and at a higher efficiency.

“This was mainly seen in women who had been iron deficient or anemic at the beginning of the trial and in women who were specifically training, including in elite athletes,” said Pasricha. “The study collected data from many individual smaller studies which generally could not identify this beneficial effect on their own. However, when we merged the data using meta-analysis, we found this impressive benefit from iron.” 

While supplements are popular, it is the first time researchers have been able to confirm that iron supplementation has beneficial effects on exercise performance, which means it is going to be trumpeted by supplement peddlers - but use some caution. The authors drew a conclusion from smaller studies which were not investigating iron and exercise. 

Nonetheless, Pasricha said the findings could have implications well-being of the general population and athletes. It's known that iron deficiency can impair exercise performance in women because it produce fatigue and lethargy and due to anemia, but this should not be read to infer that women with normal iron levels will show improvement by taking these supplements. Too much iron is also a bad thing.. 

“It may be worthwhile screening women, including women training as elite athletes, for iron deficiency, and ensuring they receive appropriate prevention and treatment strategies. Athletes, especially females, are at increased risk of iron deficiency potentially, due to their diets and inflammation caused by excessive exercise,” said Pasricha.