Purdue News

February 19, 1993

Purdue Study: If You Work Out, Work In More Iron

West Lafayette, IND. — You feel pretty good.

You have started an exercise program; you eat lots of grains, fruits and vegetables. To avoid cholesterol, you avoid red meat, choosing turkey, chicken and fish, instead.

Hold it right there. You could be headed for trouble.

Research done at Purdue University shows that today's popular, "healthy" lifestyle combining regular exercise with a low-fat, low-cholesterol diet could be a prescription for iron deficiency.

"Past research has shown that professional athletes who exercise vigorously every day need more iron," says Connie M. Weaver, head of Purdue's Department of Foods and Nutrition. "But in this study we've found that women who exercise moderately are depleted of significant amounts of iron — enough that they should be adding iron to their diets by using supplements or eating more iron-rich foods."

Funded by the National Live Stock and Meat Board and documented in the December 1992 issue of the American Journal of Clinical Nutrition, the study showed that women aged 18-25, who exercised for 50-minutes three times a week, experienced a considerable loss of iron in their blood.

Roseann M. Lyle, associate professor of health at Purdue and the study's main author, says the research provides further evidence that exercisers need to be knowledgeable about the effects of exercise. "You can't depend on exercise to be a health panacea," she says. "Good health is an intricate balance of the right exercise and the right foods — and the iron depletion evidence in this study has shown us that without the right diet, exercise can have its down side, too."

During the 12-week study, previously sedentary women who began exercising but maintained their pre-study eating habits lost five grams of hemoglobin per liter of their blood after the first four weeks, and never regained it during the remaining eight weeks. Iron is a necessary component of hemoglobin, the blood's oxygen carrier.

"That group began the study with 120 grams of hemoglobin per liter of their blood," Weaver says. "That's the smallest amount of hemoglobin you can have without being clinically anemic. In all three of the following blood tests taken at four-week intervals, their samples dropped to 115 grams and stayed at that level. As a group, they had gone from non-exercisers with just enough hemoglobin, to exercisers who were anemic."

Anemia causes a general lack of energy and a tendency toward fatigue. In more extreme cases, physical exertion can cause shortness of breath, pounding of the heart and finally, heart failure.

People with anemia also have been identified by a loss of the healthy pink hue in the palms of their hands, fingernails and conjunctiva, the eyelid lining.

Weaver says the study's other groups of exercisers also lost iron initially, but recovered the iron with replenishment. "In each case, when subjects were given iron supplement pills or they were given red meat to add to their daily intake, they made up most — if not all — of the iron loss," she says. "Those who received lean meat instead of a pill absorbed the iron better and had more iron reserves than before they started the study."

Weaver says foods will always be preferable to pills or capsules as iron sources. "Gram for gram, the iron you eat in a serving of red meat will be more readily absorbed than the iron you take from a bottle," she says. "But if you don't want to eat meat or other iron sources, pill supplements are better than not doing anything."

Iron-rich foods include all varieties of beans, grapes and raisins, tomato and apple juices, and red meat. "The general rule is that the darker the meat is, the richer it is in iron," Weaver says. "Even the dark meat in chicken has more iron than the white meat, but beef and lamb have higher iron concentrations. Those concerned with fat simply need to choose leaner, well-trimmed cuts."

The government's recommended daily allowance of iron is 15 milligrams for women and 10 milligrams for men. Weaver says women who eat balanced diets that include whole grains, vegetables and juices can be reasonably sure they are getting enough iron if they eat four ounces of red meat daily.

She adds that iron-fortified foods are not all equal. "Processed foods that are fortified with iron sulfate and iron fumarate are better sources of absorbable iron than most other supplements," she says.

Weaver also offers these hints:

• Drink citrus juice when consuming iron. Vitamin C helps the body absorb iron.

• Do not drink tea when you eat iron-rich foods. Tannins, the astringent quality in tea, inhibits iron absorption.

The researchers are following up on their findings by studying why exercise causes iron depletion. A few of the possibilities they will examine include iron loss from red-blood cell rupture due to the physical impact of exercise and loss from urination or perspiration.

Purdue News Service: (765) 494-2096; purduenews@purdue.edu