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Iron and the Effects of Exercise

Sports medicine experts have observed for years that endurance athletes, particularly females, frequently have iron deficiencies. Now a new study by a team of Purdue University researchers suggests that even moderate exercise may lead to reduced iron in the blood of women.

"We found that women who were normally inactive and then started a program of moderate exercise showed evidence of iron loss," says Roseanne M. Lyle, associate professor at Purdue. Her study of 62 formerly inactive women who began exercising three times a week for six months was published in the journal Medicine & Science in Sports & Exercise.

"Women who consumed additional meat or took iron supplements were able to bounce back," she notes. "But the new exercisers who followed their normal diet showed a decrease in iron levels."

Iron deficiency is very common among women in general, affecting one in four female teenagers and one in five women aged 18 to 45, respectively. But the ratio is even greater among active women, affecting up to 80 percent of female endurance athletes. This means, Lyle says, that "too many women ignore the amount of iron they take in";. Women of child-bearing age are at greatest risk, since their monthly bleeding is a major source of iron loss. Plus, many health-conscious women increase their risk by rejecting red meat, which contains the most easily absorbed form of iron. And because women often restrict their diet in an effort to control weight, they may not consume enough iron-rich food, and are liable to experience a deficiency.

"The average woman takes in only two thirds of the recommended daily allowance for iron," notes another expert. "For a woman who already has a poor iron status, any additional iron loss from exercise may be enough to tip her over the edge into a more serious deficiency," notes the expert.

Exercise can result in iron loss through a variety of mechanisms. Some iron is lost in sweat, and, for unknown reasons, intense endurance exercise is sometimes associated with bleeding of the digestive system. Athletes in high-impact sports such as running may also lose iron through a phenomenon where small blood vessels in the feet leak blood.

There are three stages of iron deficiency. The first and most common is having low iron reserves, a condition that typically has no symptoms. Fatigue and poor performance may begin to appear in the second stage of deficiency, when not enough iron is present to form the molecules of blood protein that transport oxygen to the working muscles. In the third and final stage, people often feel weak, tired, and out of breath — and exercise performance is severely compromised.

"People think that if they're not at the third stage, nothing is wrong, but that's not true," says John L. Beard, who helped design the Purdue study. "You're not stage 3 until your iron reserves go to zero, and if you wait until that point, you're in trouble."

However, most people with low iron reserves don't know they have a deficiency, because traditional methods of calculating the amount of iron in blood (by checking levels of the blood protein that transports oxygen) are not sufficient, Beard states. Instead, it's important to check levels of a different compound, which indicates the amount of storage of iron in the blood. While active, child-bearing age women are most likely to have low iron stores, he notes, "Men are not safe, especially if they don't eat meat and have a high level of physical activity." (An estimated 15 percent of male long distance runners have low iron stores.) Beard and other experts say it's advisable for people in these groups to have a yearly blood test to