Section (A)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 researcherssuggests 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 exerciseshowed evidence of iron loss," says Roseanne M. Lyle, associate professor at Purdue. Her study of 62formerly inactive women who began exercising three times a week for six months was published in thejournal Medicine & Science in Sports & Exercise.
"Women who consumed additional meat or took iron supplements were able to bounce back," shenotes. "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 andone 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 womenignore the amount of iron they take in";. Women of child-bearing age are at greatest risk, since theirmonthly bleeding is a major source of iron loss. Plus, many health-conscious women increase their riskby rejecting red meat, which contains the most easily absorbed form of iron. And because women oftenrestrict their diet in an effort to control weight, they may not consume enough iron-rich food, and areliable to experience a deficiency.
"The average woman takes in only two thirds of the recommended daily allowance for iron," notesanother expert. "For a woman who already has a poor iron status, any additional iron loss from exercisemay 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, forunknown reasons, intense endurance exercise is sometimes associated with bleeding of the digestivesystem. Athletes in high-impact sports such as running may also lose iron through a phenomenonwhere 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, acondition that typically has no symptoms. Fatigue and poor performance may begin to appear in thesecond stage of deficiency, when not enough iron is present to form the molecules of blood protein thattransport oxygen to the working muscles. In the third and final stage, people often feel weak, tired, andout 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, andif you wait until that point, you're in trouble."However, most people with low iron reserves don't know they have a deficiency, because traditionalmethods of calculating the amount of iron in blood (by checking levels of the blood protein thattransports oxygen) are not sufficient, Beard states. Instead, it's important to check levels of a differentcompound, which indicates the amount of storage of iron in the blood. While active, child-bearing agewomen are most likely to have low iron stores, he notes, "Men are not safe, especially if they don't eatmeat and have a high level of physical activity." (An estimated 15 percent of male long distance runnershave low iron stores.) Beard and other experts say it's advisable for people in these groups to have ayearly blood test to check blood iron reserves.
If iron levels are low, talk with a physician to see if the deficiency should be corrected by modifyingyour 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 mayproduce 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.
"Select breads and cereals with the words 'iron-added' on the label," writes sports diet expert NancyClark. "This added iron supplements the small amount that naturally occurs in grains. Eat these foodswith plentiful Vitamin C (for example, drink orange juice with cereal or put a tomato on a sandwich) toenhance the amount of iron absorbed." Clark also recommends cooking in iron pans, as food can deriveiron from the pan during the cooking process. "The iron content of tomato sauce cooked in an iron potfor three hours showed a striking increase, the level going up nearly 30 times," she writes. And peoplewho are likely to have low iron should avoid drinking coffee or tea with meals, she says, sincesubstances in these drinks can interfere with iron being absorbed into the body.
"Active women need to be a lot more careful about their food choices," sums up Purdue's Lyle. "Ifyou pay attention to warning signs before iron reserves are gone, you can remedy the deficiency beforeit really becomes a problem."
New Words
▲endurance n. 忍耐，忍耐力
moderate a. 1.中等的，适中的，适度的 2.中庸的，温和的
evidence n. 根据，证据，证明
journal n. 1.日报，杂志，期刊 2.日记
consume vt. 1.吃，喝 2.消耗，花费（尤指大量地）
supplement n. 1.增补(物)，补充(物) 2.（杂志或报纸的）副刊，增刊
vt. 增补，补充
bounce v. （使）弹回，（使）反弹
n. 弹，弹力
respectively ad. 分别地，各自地
ratio n. 比率
plus conj. 并且，而且
prep. 加，加上
n. 1.加号，正号 2.有利因素
a. 正的
restrict vt. 限制，约束
liable a. 1.易于... ...的，有... ... 倾向的 2.有法律责任的，有义务的
allowance n. 1.限额，定量 2.津贴，补助，零用钱
digest vt. 1.消化 2.领会
digestive a. 消化的
phenomenon n. 现象
vessel n. 1.血管，脉管 2.容器，器皿 3.船，舰
typical a. 典型的，有代表性的
◆typically ad. 典型地，有代表性地
fatigue n. 疲劳，劳累
molecule n. 分子
protein n. 蛋白质
calculate vt. 1.计算，估算 2.认为，相信，推测
sufficient a. 足够的，充分的
compound n. 复合物，混合物
indicate vt. 1.标示，表明 2.指示方向
storage n. 储存，储藏
advisable a. 可取的，适当的，明智的
yearly a. 每年的，一年一度的
physician n. 内科医生
modify vt. 修改，更改，改善
undo vt. 1.取消，消除 2.解开，松开
shortcoming n. 缺点
select vt. 选择，挑选
▲cereal n. 谷类作物，谷类食物（如麦片等）
plentiful a. 大量的，丰富的
derive v. 1.得到，获取 2.起源于
striking a. 1.显著的，突出的，惊人的 2.（由于美貌而）引人注目的，吸引人的
interfere vi. 1.妨碍，干扰 2.干涉，干预
remedy vt. 补救，纠正
n. 治疗方法，解决方法
Phrases and Expressions
lead to 导致
bounce back 恢复正常，恢复过来
in general 大体上；通常
up to 至多，多达，直到
take in 吸入，吞入
at risk 处在危险之中
tip over the edge 引起明显变化；(使)进入另一状态
out of breath 呼吸急促，气喘吁吁
add sth. to 加，增加，添加
throw up 恶心，呕吐
go up （价格、水平等）升高，上升
sum up 概括，总结
Proper Names
Purdue University 珀杜大学
Roseanne M. Lyle 罗斯安妮·M.莱尔
Medicine & Science in Sports & Exercise 《体育运动医学与科学》(期刊名)
John L. Beard 约翰·L.比尔德
Nancy Clark 南希·克拉克 |