Iron and the Effects of Exercise 铁和运动效果的接洽

Iron and the Effects of Exercise

Para 1Sports 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.

Para 2“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.

Para 3“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.”

Para 4 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 childbearing 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.

Para 5 “The average woman takes in only two thirds of the recommended daily allowance of 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.

Para 6Exercise can result in iron loss through a variety of the 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.

Para 7 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. Pare 8“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 in stage 3 until your iron reserves go to zero, and if you wait until that point, you?re in trouble.”

Pare 9However, 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 indicate the amount of storage of iron in the blood. While active, childbearing 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 check blood iron reserves. Pare 1o If iron levels are low, talk with a physician to see if the deficiency should be corrected by modifying your diet or by taking supplements. In general, it?s better to undo the problem by adding more iron-rich foods to the diet, because iron supplements can have serious shortcomings. Supplements may produce a feeling of wanting to throw up, and may be poisonous in some cases. The best sources of iron, and

the only sources of the form of iron most readily absorbed by the body, are meat, chicken, and fish. Good sources of other forms of iron include dates, beans, and some leafy green vegetables.

Pare 11“Select breads and cereals with the words …iron-added?on the label,” writes sports diet expert Nancy Clark. “This added iron supplements the small amount that naturally occurs in grains. Eat these foods with plentiful Vitamin C(for example, drink orange juice with cereal or put a tomato on a sandwich) to enhance the amount of iron absorbed.” Clark also recommends cooking in iron pans, as food can derive iron from the pan during the cooking process. “The iron content of tomato sause cooked in an iron pot for three hours showed a striking increase, the level going up nearly 30 times,” she writes. And people who are likely to have low iron should avoid drinking coffee or tea with meals, she says, since substances in these drinks can interfere with iron being absorbed into the body.

Pare 12“Active women need to be a lot more careful about their food choices,” sums up Purdue?s Lyle. “If you pay attention to warning signs before iron reserves are gone, you can remedy the deficiency before it really become a problem .

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铁与运动的关系

运动医学专家经过多年的观察,发现耐力运动员,特别是女性,经

常会缺铁。普渡大学研究人员进行的一项新的研究表明,即使是适度

的锻炼,也可能会降低女性血液中的铁含量。

“我们发现,那些通常不运动的女性一旦开始适度的锻炼,就会出现铁含量下降的迹象。”普渡大学罗斯安妮·M.莱尔副教授说。她对62名妇女进行了研究，并将研究结果发表在《体育运动医学与科学》杂志上。这些妇女原先不怎么运动，后来开始了为期6个月、每周

3次的锻炼。

莱尔指出：“那些增食肉类食品或服用铁质补剂的女性能够恢

复到健康状态。但突然参加锻炼却仍沿用旧食谱的人则显示出铁含

量降低。”

缺铁在女性中是很常见的，每四个十几岁的少女中有一人缺铁

每五个18至45岁的女性中有一人缺铁。而在积极锻炼的妇女中

这一比例更高。女耐力运动员中，缺铁者比例则高达80%。莱尔说，这意味着“太多女性忽视了自己摄入的铁含量”。育龄女性危险最大，因为月经是铁流失的重要原因之一。此外，许多保健意识太强的女

性也很危险，因为她们拒绝食用牛肉或羊肉。而这些肉中含有的铁

最易被吸收。而且，由于女性常常为了控制体重而节食，从而未能

摄取足够的含铁丰富的食物，结果可能导致缺铁。

另一名专家指出 “普通女性每天摄入的铁只是应摄入量的三

分之二。”他指出：“对于那些已经缺铁的女性，任何因锻炼而产生的更多铁质流失都足以导致体内缺铁状况的恶化。”

运动可能通过多种机制导致铁流失。有些铁随汗液流失。另外

由于某些未知的原因，高强度的耐力运动有时会引起消化系统内出血。运动员从事跑步之类高强度剧烈运动，也可能会因为足部血管失血的现象而使铁质流失。

缺铁分为三个阶段。第一也即最常见的阶段，是铁质储量不足。这一阶段一般没有症状。到了缺铁的第二阶段，就会出现疲倦和力不从心，此时体内已没有足够的铁来形成血蛋白分子，将氧输至运动肌肉。在第三即最后阶段，人常常感到虚弱、疲乏无力、喘不过气，运动成绩大打折扣。

“人们认为，只要不到第三阶段就不会有什么问题。这种想法是不对的。”帮助设计普渡大学研究的约翰·L.比尔德说。“只有当你

的铁储量为零时，你才会进入第三阶段。而你若坐等到这个时候，你的麻烦就大了。”

然而，比尔德指出，大多数铁质储量低的人并未意识到自己缺铁。因为传统的检验血液中铁含量的方法——检验血液中输送洋气的血蛋白的含量——是不够的。其实，有必要检查血液中另一种混合成分的含量，它可以显示血液中的铁含量。他还指出，虽然积极锻炼的育龄妇女最有可能铁含量低，“但男性也并非不缺铁，尤其是在他们不吃肉类而又从事高强度的体力活动的情况下。”估计有15%的男性长跑运动员铁含量低。比尔德和其他专家都说，对这些人而言，最好每年验一次血，以测定血液中的铁含量。

如果铁含量低，就要去看医生，以确定是否该通过调整饮食或服用铁质补剂来校正不足。一般说来，解决问题是最好方法是在食

谱中增加含铁丰富的食物，因为铁质补剂可能存在严重缺陷。服用

铁质补剂可能使人想呕吐，有时甚至还会引起中毒。最好的铁来源，以及唯一最易为身体所吸收的铁来源，是肉、鸡和鱼。其他较好的

铁质来源包括枣、豆类和一些多叶绿色蔬菜。

“选择那些标有‘加铁’字样的面包和麦片。”运动营养专家南希·克拉克写道，“这些增加的铁质补充了谷物中自然含铁量的不足。将这些食物与含有大量维生素C的食物一起食用——比如吃麦片时

喝橘子汁，或在三明治内夹上番茄——可以促铁质吸收。”克拉克还建议用铁锅烹食，因为烹调过程中食物能从铁锅中吸收铁质。她写道：“在铁锅内烹煮了3个小时的番茄汁，其含铁量大大提高，增

加到原来的30倍左右。”她说，铁含量可能低的人，吃饭时应避免

喝咖啡或饮茶，因为这些饮料中所含的物质会妨碍身体对铁质的吸收。

“运动女性应特别注意选择饮食。”普渡大学的莱尔总结说：

“如果你在铁含量流失之前就注意到了警告信号，你就可以在它真

正成为问题之前弥补铁质的不足。”