1st April 2004
NEW YORK (Reuters Health) - Some women who are short on iron may be short on endurance as well, even when they do not have full-blown anemia, new study findings suggest.
On the bright side, researchers report, getting enough iron may help correct the problem.
Their study of 41
women who were moderately iron deficient found that iron supplements
helped boost fitness among those with more depleted iron stores in
their body tissue.Thomas Brownlie and his colleagues at Cornell University in Ithaca, New York, report the findings in the American Journal of Clinical Nutrition.
Iron-deficiency anemia occurs when the body has too little hemoglobin, an iron-containing protein in red blood cells that carries oxygen. Anemia is well known to cause fatigue, pale skin and breathlessness during exercise, but the effects of less severe iron deficiency are not as clear.
Animal studies have suggested it can sap endurance, but human studies have not consistently shown this, according to Brownlie's team.
To study the question, the researchers looked at whether iron supplements would help modestly iron-deficient women get more out of exercise training. They had 41 iron-depleted -- but not anemic -- women between the ages of 18 and 33 take either iron supplements or placebo pills for six weeks. All of the women spent the last four weeks of the study training on stationary bikes five days a week.
Brownlie and his colleagues also looked specifically at a measure called serum transferrin receptor (sTfR) concentration, which indicates the iron status of the body's tissues. A higher concentration means greater iron deficiency in the tissue.
The researchers found that iron supplements appeared to help women with signs of "overt" tissue iron depletion make greater fitness gains during their exercise regimen.
In contrast, the supplements provided no fitness benefit to women with normal sTfR levels, who improved their endurance regardless of whether they took iron or not. This suggests that their degree of iron depletion had not been limiting their endurance in the first place, according to Brownlie's team.
The findings also indicate that a person's sTfR levels can help distinguish diminished iron levels from a more problematic iron deficiency, the researchers note. If iron depletion is impairing fitness, they conclude, supplements may help correct the problem.
Iron supplements can, however, cause side effects such as abdominal pain, nausea, constipation and diarrhea, and experts advise consumers to consult a doctor before taking iron supplements.
They also recommend that people look at their diets before turning to pills; good food sources of iron include red meat, lentils and other legumes, spinach and iron-fortified cereals and grains.
The current study was partially funded by a grant from Mead Johnson Nutritionals, a Bristol-Myers Squibb company that makes dietary supplements.
SOURCE: American Journal of Clinical Nutrition, March 2004.