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托福阅读材料：缺乏维他命可能导致帕金森症

2015-01-15 17:57:22来源：网络

　　In the second study, David Llewellyn of the University of Exeter and colleagues examined vitamin D levels among 858 Italian men and women age 65 and older. They found that more than half of the participants with dementia were vitamin D deficient (<50 nmol/L). What's more, cognitive tests revealed that severely deficient individuals (<25 nmol/L) were 60 percent more likely to undergo cognitive decline over the six-year follow-up period. This study appears online July 12 in the Archives of Internal Medicine.

　　Humans can obtain vitamin D by eating oily fish or fortified foods, and it is also photosynthesized in the skin upon exposure to adequate amounts of ultraviolet B (UVB) rays in sunlight. Major factors that influence vitamin D status in humans include season, latitude, age, skin tone, diet and supplement use. The U.S. Institute of Medicine currently recommends that adult men and women aim for a daily intake of 200-600 International Units (IU) of vitamin D.

　　New guidelines for vitamin D intake were published online July 12 in the Canadian Medical Association Journal by scientists from Osteoporosis Canada, a non-profit organization. Because vitamin D influences calcium absorption and may protect against osteoporosis, the authors advise an increased daily intake of 400-1000 IU for healthy Canadians under age 50, and up to 2000 IU for those older than 50. The researchers state the changes are necessary because winter sunlight north of the 35th parallel (which coincides with the southern border of Tennessee) provides insufficient UVB for people living in that region to adequately make vitamin D.

　　The studies by Knekt and Llewellyn are not the first to link vitamin D deficiency with neurological problems, however. A role for vitamin D has previously been suggested in multiple sclerosis, autism and schizophrenia.

　　Some experts advise interpreting the results of these and other observational studies of vitamin D with caution. The above studies relied on participants from specific geographic areas, so more study is needed to determine whether the findings apply to other regions. Furthermore, "low vitamin D levels may simply be a marker for lower health status rather than a cause of it," Andrew Grey, professor of medicine at the University of Auckland, wrote in an editorial in the Archives of Internal Medicine. This is because vitamin D levels are directly related to sunlight exposure and physical activity; less healthy individuals are therefore likely to be less active and more sunlight-deprived, and have lower levels of vitamin D.

　　"It is now time to test the various hypotheses generated by observational studies of vitamin D…in adequately designed and conducted randomized controlled trials," Grey concluded. "We should invest in trials that provide the best possible evidence on the benefits and risks of vitamin D before we invest in costly, difficult, and potentially unrewarding interventional strategies."

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