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  3. Dietary studies have suggested that people who consume large amounts of vitamin A in foods, multi vitamins, or both are more lik

Dietary studies have suggested that people who consume large amounts of vitamin A in foods, multi vitamins, or both are more lik

admin2011-10-20  65
问题     Dietary studies have suggested that people who consume large amounts of vitamin A in foods, multi vitamins, or both are more likely to suffer hip fractures than are people who ingest modest amounts.
    New evidence bolsters these findings. Researchers have now correlated men’s blood concentrations of vitamin A with a later incidence of broken bones: a comparison that avoids the vagaries that plague diet-recall studies.
    Taken together, the new work and the diet studies raise knotty questions about the maximum amount of vitamin A that a person can safely ingest each day, says study coauthor Karl Michasson, an orthopedic surgeon at University Hospital in Uppsala, Sweden. He and his colleagues report the new findings in Jan. 23 New England Journal of Medicine.
    In the United States, the average daily intake of vitamin A through food, specially fish, eggs, and meat, is roughly 2,600 IU (international units) for men, and many multi-vitamins contain 5,000 IU. The US Institute of Medicine recommends that people get 2,300 to 3,000 IU of vitamin A each day and sets the safe upper limit around 10,000 IU.
    "I believe tiffs upper level should be lowered," Michasson says. When he and his colleagues gave the men dietary questionnaires, they learned that men ingesting as little as 5,000 IU of vitamin A per day were more prone to fractures than were men getting less. Manufacturers should lower the amount of vitamin A in multi-vitamin tablets and fortified foods, such as cereals, says Michasson.
    The new study began in the early 1970s when researchers stored blood samples from 2,047 men about 50 years old. Since then, 266 of the men have had at least one bone fracture. After dividing the men into five equal groups according to their blood vitamin A concentrations, the researchers found that men in the top group were nearly twice as likely as those in the middle group to have broken a bone. The correlation was particularly strong with fractures of the hip.
    "I think it’s pretty conclusive now that there’s a bad effect of vitamin A supplementation," says Margo A. Denke, an endocrinologist at the University of Texas Southwestern Medical Center in Dallas. Elderly people may be at special risk because they’re slow to clear the vitamin from their bodies. Studies of animals have established that excess vitamin A stimulates the formation of cells that dissolve bone.
    However, since some vitamin A is necessary to maintain good eyesight and general health, Denke and Michasson agree that fully fortified foods and supplements should remain available in countries where poor nutrition puts people at risk of a vitamin A deficiency.
选项 A、a man taking large amounts of vitamin A will suffer hip fractures.
B、the maximum of vitamin A a man takes every day should be within 3,000 IU.
C、the more a man consumes vitamin A every day, the higher chance he suffers hip fracture.
D、the less a man consumes vitamin A every day, the higher chance he stands of good health.
答案C
解析 推理题。文章开头提出从饮食中大量摄入维生素A更容易导致骨折，从而得出结论：摄入维生素A的量越大，得骨折的可能性越高，所以答案选项符合文意；但不能推出"大量摄取维生素A的人会骨折"；文章第四段提到建议每人每天摄人维生素A的量在2,300—2,000 IU之间，最高限量不超过10,000 IU，所以"最高限量低于3,000 IU"的说法是错误的；"每天摄人维生素A的量越少，身体越健康"，文章末尾处提到维生素A对维持视力和全身健康是必不可少的，所以该项也不正确。
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