A recent supplement to Medicine & Science in Sports & Exercise® covered gender factors contributing to performance and musculoskeletal injury in Israeli military recruits. Iron deficiency anemia was a key gender factor, but two large studies differed in findings among male recruits. In one study of 438 recruits, iron deficiency anemia was found in approximately 18% of the women and 8% of the men (11). In the other study, of 348 recruits, using more stringent diagnostic criteria, iron deficiency anemia was found in approximately 13% of the women but in none of the men (8). This finding that iron deficiency anemia is common in Israeli female soldiers agrees with research in the U.S. military (10). But the mixed results on "iron deficiency anemia" in Israeli male soldiers suggest that in men, dilutional pseudoanemia (called "sports anemia" in previous times) can be mistaken for iron deficiency anemia.
SPORTS ANEMIA: NATURE'S ANTICOAGULANT
Pearl: The most common cause - in a male athlete or soldier - of a slightly low hemoglobin level, say down to 13 g·dL−1 or so, is not iron deficiency anemia, but "sports anemia," the opposite of "sofa spud's blood." Let me explain.
The blood of sedentary individuals (sofa spuds) has a fourfold problem: 1) elevated hemoglobin level, or "thick blood"; 2) elevated plasma fibrinogen level; 3) hyper-reactive platelets; and 4) sluggish fibrinolysis. These four factors make the blood hard to pump and prone to clot. They contribute to cardiovascular risk. The good news is that all four can be reversed by regular exercise. In this sense, exercise is nature's anticoagulant.
THE BLOOD OF ATHLETES
Athletes, soldiers, and other active people tend to have lower hemoglobin levels than do their sedentary counterparts, because regular exercise is a "plasma-builder." In response to the temporary dehydration from a workout, the body adds salt, water, and albumin to the blood, expanding baseline plasma volume (7,12). Just one brief, vigorous workout can expand plasma volume by up to 10% within 1 d (7). In a recent study, just two 30-s, high-intensity cycling bouts increased plasma volume by 4% the next day (14). Regular exercise keeps the plasma volume expanded, "thinning" the blood in a healthy way (3).
Regular exercise also can reverse the other three facets of the sofa spud's blood. Most, but not all, studies of exercise and fibrinogen suggest that regular exercise can dilute down baseline fibrinogen level. On balance, regular exercise also can reduce platelet reactivity and enhance baseline fibrinolysis (1,2,5). In concert, this research suggests that the blood of an athlete flows more easily and clots less readily.
PSEUDOANEMIA CONTRIBUTES TO AEROBIC FITNESS
Ironically, "sports anemia," a dilutional pseudoanemia, seems to be a cardinal component of aerobic fitness. One might expect the lower hemoglobin level per unit of blood to curb maximal exercise performance. This drawback, however, may be more than offset by the increase in cardiac stroke volume caused by the larger blood volume and the adaptations of "athlete's heart." If so, the Fick equation predicts that dilutional pseudoanemia enhances oxygen delivery to muscles (3).
Another study in the Israeli military suggests that the main cause of lower hemoglobin levels in male soldiers is not iron deficiency anemia, but dilutional pseudoanemia. When 48 submarine trainees and 48 naval Special Forces trainees were tracked for 2 yr, hematocrit fell only in the Special Forces trainees, who, unlike the submarine trainees, had long-term endurance training. In other words, only the "endurance soldier-athletes" developed dilutional pseudoanemia (9).
The contrasting fitness aspects of sofa spud's blood, dilutional pseudoanemia, and iron deficiency anemia also may explain the fascinating results of a recent study of Israeli (male) infantry recruits. When 358 recruits had their blood tested, approximately 50% had hemoglobin under 14 g·dL−1 and approximately 5% had hemoglobin under 12 g·dL−1. Fitness was tested by time to run 2000 m. The result: Men with intermediate hemoglobin values (12-14 g·dL−1) ran faster - were more fit - than men with the lowest values (<12 g·dL−1) or men with the highest values (>14 g·dL−1). Men with the lowest values included some with true iron deficiency anemia, and men with the highest values likely included some sofa spuds (13). Conclusion: Moderation is best in all things, including hemoglobin value.
PEARL: WOMEN ARE DIFFERENT FROM MEN
The Israeli military researchers were correct to conclude that iron deficiency anemia is a key problem for females, and that "iron deficiency" is eight times more prevalent in female than in male military recruits (11). This gender difference in iron deficiency occurs because women lose iron in menses and consume less than half the dietary iron that male recruits consume (6). Finding and treating iron deficiency anemia in female soldiers and athletes is critical to health and performance. In a prior column (4), I covered iron deficiency anemia in female athletes and offered practical tips on how they can absorb more iron from diet. These include: 1) eat more lean red meat; 2) avoid tea or coffee with meals; 3) consume orange juice or another source of vitamin C with breakfast; 4) cook in cast-iron cookware; and 5) eat mixed meals, so the protein factor in meat, fish, and poultry will enhance iron absorption from grains, beans, and legumes. If iron and calcium supplements are taken, space them out so the calcium will not inhibit iron absorption.
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