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找到合成维生素D的最佳时间

更新时间:2014-1-24 13:58:55 来源:华尔街日报中文网 作者:佚名

Find The Best Times For Vitamin D
找到合成维生素D的最佳时间

The Ache: Doctors say one of the best sources of vitamin D, which is important for bone health, is sunlight. But the amount of ultraviolet rays reaching the Earth varies by location and season.

The Claim: The dminder iPhone app tells users what days and times vitamin D can be made based on location. When you tell the app you're in the sun, it shows a running estimate of your vitamin D production.

The Verdict: The app is based on published scientific studies conducted at Boston University. But it hasn't been tested in a clinical study to see how accurate its estimates are in real-life use.

About a third of the U.S. population may not be getting enough vitamin D, according to the U.S. National Center for Health Statistics. Part of the problem is people don't spend enough time outside and when they do, it may not be at the ideal time to make vitamin D, says Michael F. Holick, a professor of medicine at Boston University who teamed up with RobCo Inc. of Los Angeles, which does business as Ontometrics, to develop the app. Wearing sunscreen will greatly reduce vitamin D production.

The app is free for the basic version and $1.99 for a version that keeps a log of vitamin D production and supplements taken. It plugs data from the Environmental Protection Agency's 'ultraviolet index,' a measure of ultraviolet-ray intensity at a location and time, into an algorithm that includes a person's skin type and age, says Ontometrics Chief Executive Rob Williams. It's based on Dr. Holick's research, which examined factors causing variations in vitamin D production.

According to the research, in many areas of the U.S. a person can't make any vitamin D from November through February. That's because the sun is low in the sky and, as the ultraviolet B rays that stimulate vitamin D production have to travel through a longer distance of ozone layer, most or all are absorbed before they reach the Earth's surface.

The app alerts users to when adequate ultraviolet light to make vitamin D will reach the Earth's surface in their location. On Monday, the app predicted the next vitamin D making opportunity in Boston is on Jan. 31. In New York, the next opportunity is in four days. People in southern locations could make vitamin D on Friday, but only at certain times. In Atlanta, the app showed a window of opportunity from 11:14 a.m. to 2:22 p.m.

Robyn Lucas, a vitamin D researcher and professor at Australian National University in Canberra, says the app's methodology appears 'reasonably legitimate' as it's well established that the time of day and season affects vitamin D production. But the exact numbers of vitamin D production are unlikely to be accurate for individuals as there are too many variables, Dr. Lucas says. For example, you make more if you are lying horizontally with your skin facing the sun directly than standing, she adds.

The app assumes you are lying down, says Mr. Williams, but a future version may take into account your position.

Yale University Dermatology Professor David Leffell says people with fair skin, or a family history of melanoma, should be 'cautious about relying on the sun' to make vitamin D, and particularly about relying on an app that hasn't been tested in clinical trials. Those people would be better off talking to their doctor about taking supplements, he adds.

缺点:医生说,阳光是维生素D的最佳来源之一。维生素D对于骨骼健康非常重要。但到达地球表面的紫外线量受制于地区和季节的变化。

用途:这款iPhone应用软件可以依据使用者所在的位置预测何日何时可以合成维生素D。当你告诉这款应用软件你站在太阳地里,它就会运行评估你的维生素D合成情况。

结论:这款应用基于波士顿大学(Boston University)已经公布的科学研究结果,但还未经过临床测试,因此无法确定在实际生活中准确程度如何。

据美国国家健康统计中心(U.S. National Center for Health Statistics)统计,大约三分之一的美国人没有获得足够的维生素D。波士顿大学医学教授霍利克(Michael F. Holick)称, 这在一定程度上是因为人们户外活动的时间不足,而当他们进行户外活动时,又可能不是合成维生素D的理想时间。霍利克和洛杉矶的RobCo Inc.公司(开展业务时的用名为Ontometrics)共同研发了这款应用软件。涂防晒霜会大大降低维生素D的合成。

这款软件的基本版是免费的,包含维生素D合成和补充剂服用记录的版本的费用为1.99美元。Ontometrics首席执行长威廉斯(Rob Williams)称,该软件将环境保护局(Environmental Protection Agency)发布的“紫外线指数”中的数据填入一个方程式中,该方程式包含人的皮肤类型和年龄。该方程式以霍利克的研究为基础,霍利克研究了影响维生素D合成的各种因素。“紫外线指数”是衡量特定位置和时间紫外线强度的指标。

根据上述研究,美国许多地区的人在每年的11月至次年的2月无法合成维生素D。这是因为太阳在天空中的位置很低,而刺激合成维生素D的紫外线B射线(UVB)必须在臭氧层中穿越更长的距离,大部分乃至全部UVB在到达地球表面之前已经被吸收。

这款应用软件可以提醒使用者可合成充足维生素D的紫外线何时能到达他们所在的地球表面。周一,这款软件预计波士顿的下一个维生素D合成机会是1月31日;在纽约,下一个机会是四天后。南方地区的人们可以在周五合成维生素D,但只在某些特定的时间。在亚特兰大,这款软件显示时间窗口为上午11:14到下午2:22。

维生素D研究者、堪培拉澳大利亚国立大学(Australian National University)教授卢卡斯(Robyn Lucas)称,因为充分考虑到了影响维生素D合成的时间和季节因素,这款软件的方法似乎符合逻辑。但卢卡斯表示,由于存在太多变量,每个人合成维生素D的具体数字不太可能非常准确。例如,如果你面向太阳水平躺倒时要比直立时能合成更多的维生素D。

威廉斯称,这款应用软件假定你是躺倒的,未来的版本可能会将你的姿势考虑在内。

耶鲁大学(Yale University)皮肤病学教授莱佛尔(David Leffell)称,皮肤白皙或者家族有黑素瘤病史的人不应当依赖太阳光合成维生素D,特别是不能依赖一款未经过临床测试的软件。他补充说,这些人最好与他们的医生谈谈服用补充剂的问题。

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