【双语阅读】Can tablet screens disrup sleep?

2012-11-25

Can tablet screens disrupt sleep?

Are you worried that using your tablet screen in bed at night may stop you getting a good sleep? You may well be, following a spate of headlines reporting on the work of scientists at the Lighting Research Centre, part of the Rensselaer Polytechnic Institute in New York.

Mariana Figueiro led a team of scientists who found that exposure to the light from self-luminous displays, such as Apple iPads, could be "linked to increased risk for sleep disorders because these devices emit optical radiation at short wavelengths, close to the peak sensitivity of melatonin suppression".

Melatonin is a hormone used by the body as a biological indicator of how dark it is outside. It is often used by travellers to get over jet lag, and works by helping the body to adjust its circadian clock to match the time zone.

In Figueiro's experiment, carried out on 13 volunteers aged around 20, the scientists found that two hours of iPad use before bedtime suppressed the body's melatonin levels by around 23%. (The researchers also measured melatonin suppression after an hour of iPad use but found no statistically significant change).

The study, published recently in the journal Applied Ergonomics, has received a lot of attention and has already led commentators to plead for a self-imposed break on computer use at night.

However, Russell Foster, a professor of circadian neuroscience at the University of Oxford, is not convinced.

For a start, he said, melatonin levels were not a good way to predict how much sleep someone will get.

"The relationship between melatonin and sleep is completely flawed, " he said. "Melatonin is not a sleep hormone – what it does is provide a biological representation of the dark. There is no empirical evidence that suggests that lower levels of melatonin will have a direct effect on the sleep axis.

"If you take melatonin, it can speed up the shifting effect of light on the clock and, in some people, has a slight sleep-inductive effect. Making the jump from the biology of what we know of melatonin to the effect it's having on sleep is completely flawed."

The levels of light needed to suppress melatonin are an order of magnitude different from the amount of light needed to shift a person's body clock. In Figueiro's study, the participants experienced light exposure levels that ranged from 5 to 50 lux. Foster said a person would need around 500 to 1, 000 lux to shift their circadian clocks.

He said the issue at stake was an important one, namely the potential adverse effects of light and use of computer and television screens on sleep, the body's circadian system and brain alertness.

"Does this paper give us any empirical evidence of the effects of light on the clock? No it doesn't, " he said. "Extrapolating from these data into a more global effect can't be done."

Foster advised people not to get unduly concerned as a result of Figueiro's research. "On the basis of these data, we cannot say anything empirical about sleep; I wouldn't worry. The bigger issue of the impact of light, particularly before you go to bed, is serious – there may well be effects of light on alertness."

One final thing that very few of the news reports on the research have mentioned: the study was funded by Sharp Laboratories of America, the research organisation run by Sharp Corporation, the electronics company that makes TVs, PCs and tablets. They produced their own tablet in 2010 but subsequently dropped it and launched a new one in March, the catchily titled RW-T110.

平板电脑屏幕会扰乱睡眠吗?

你是否担忧晚上在床上使用平板电脑会影响睡眠质量?根据大量关于纽约伦斯勒理工大学光能研究中心科学家研究工作的报道表明,这种担忧是有必要的。

玛丽安娜·菲戈罗及其领导的一组科学家们研究发现,睡眠障碍者数量的增长与使用iPad等平板电脑有关,因为“这些自发光显示设备造成的短波光辐射已经接近褪黑素抑制的峰值灵敏度”。

我们的身体通过褪黑素这种激素的生物指示作用来判断外界的黑暗程度。它通常用在旅行者需要调整飞行时差使生物钟适应时区时。

菲戈罗做了一个实验,让13名20岁左右的志愿者在睡前使用2小时iPad,结果他们的褪黑素水平被抑制了23%。(研究还测量了使用1小时iPad后的结果但并没有发现明显的数据变化)。

这一研究最近发表在了应用人体工程学杂志上并引发了关注,评论因此要求人们在夜间使用电脑时注意自觉休息。

然而牛津大学的生物科学教授卢瑟尔·福斯特对此观点并不认同。

他首先表示褪黑素水平并不能很好的反映睡眠时间的长短。

“褪黑素与睡眠的关系并不完全对应,”他接着说,“褪黑素不是睡眠激素——它只是身体在黑暗环境中的生物指示。没有实验证据显示较低的褪黑素水平对睡眠有直接影响。”

“如果你服用褪黑素,生物钟的昼夜节律现象会加速,对某些人会有微小的促进睡眠的作用。从我们所了解的关于褪黑素的生物知识判断它对睡眠的影响的想法是完全错误的。”

抑制褪黑素与改变生物钟所需要的光比起来是微不足道的。菲戈罗的报告里实验参与者所接受的光仅仅只有5到50勒克斯。而据福斯特说改变一个人的生物钟需要约500至1000勒克斯的光。

他说真正有威胁的事情才是紧要的,那就是光源潜在的有害影响,睡觉时用电脑或看电视,生物钟和大脑的警告。

“这份报告是否提供给我们了有关光源对生物钟影响的实验证据?答案是否定的。”他说,“从这些数据并不能推断出它是一种全球性现象。”

福斯特建议人们不要过度关注菲戈罗的研究结果。“基于这些数据,我们并不能得出实验性的有关睡眠的结论;我就不会担忧。事实上光在其它时候对我们的威胁警告远要严重得多,尤其是睡前。”

最后还有一件研究提及但鲜有新闻报道的事情:这项研究是由美国夏普实验室资助的,研究组织由夏普公司运营,该电子公司同时也生产电视、个人电脑和平板电脑。2010年夏普推出了自己的平板电脑,但紧接着便在3月推出了新版取代之前的产品,并诱惑性地将其命名为RW-T110。

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