the dreaded blues of dark winter months have long been blamed for seasonal depression, but too much sunshine may have an even more dire effect.
in northern greenland more than 80 percent of suicides occur in summer, during which the sun barely dips below the horizon.
"there is so much light that people can't take it," said lead study author karin sparring björkstén of the karolinska institutet in sweden.
the researchers studied records of causes of deaths—1,351 due to suicide—between 1968 to 2002 in greenland, which is largely above the arctic circle.
when they looked at the data on a month by month basis, it became clear that suicides were far more frequent in summer, particularly in the north, where the extended summer days are most pronounced.
of the 33 suicides that had occurred in the most northerly province, avannaa (north greenland), 82 percent had happened during the period of 24-hour sunlight, march 7 to october 8. (avannaa disappeared from maps in early 2009, when greenland's administrative divisions were revised.)
(related: "'death maps' pinpoint mortality causes.")
dangers of 24-hour living
across greenland, a province of denmark, 80 percent of the suicide victims were men. ninety-five percent of the victims took their lives in violent ways—shooting themselves, hanging themselves, or jumping, for example. there was no evidence that the summer increases were related to depressive disorders or increased alcohol consumption.
björkstén and her colleagues believe the increase in summer suicides is related to lack of sleep.
"people live their lives differently during the arctic summer. farmers plough their fields in the middle of the night, and children are out playing after midnight. they lose their daily rhythm," björkstén said.
other countries may not have the extreme seasonal sunlight variations, but anyone can learn from the new research, she said.
"today's 24-hour society is not good for us. public health would improve if people cared more about their sleep," said björkstén.
令人恐惧、忧郁的漫长冬季常常被视作为季节性抑郁的罪魁祸首，但是过多的日照也许会产生更加可怕的效果。
在格林兰的北部地区，超过80%的自杀事件发生在夏季，因为在那段时期里太阳很少会照射到地平线以下的区域。
“太多的日照人们无法承受”瑞典卡罗林斯卡学院领导此次研究的作者karin sparring björkstén这样说。
研究者们研究了格林兰自1968至2002年间导致死亡的原因，其中有1351例是因为自杀。格林兰的大部分地区都在北极圈内。
党研究者按照月份为基础研究数据的时候发现，显然自杀事件在夏季发生的频率更高，在北部地区尤为如此，因为在北部地区，夏季的天数更多这一特点最为显著。
在北格林兰地区的avannaa，这个格林兰最北部的省发生的33起自杀事件中，有82%发生在3月7日至10月8间。这段时期，日照长达24小时。(因为格林兰的行政划分改变，从2009年早些时候起，avannaa已经从地图上消失)
(相关：“‘死亡地图’：精确死亡原因”)
24小时生活的威协
作为丹麦的省份之一，整个格林兰80%自杀者的都为男性。95%的自杀者都用剧烈的方式结束了他们的生命，比如，枪杀，上吊自杀，跳楼。没有证据表明夏季天数的增加舆抑郁症或者酒精销量的增加有关。
björkstén和她的同事相信夏季自杀事件增多舆缺乏睡眠有关。
“北极圈内的人们夏季生活的方式有所不同。农民们在半夜耕田，而孩子们则在半夜后到外面去玩。他们日常生活的规律被打乱了。”björkstén说。
其它国家也许不会有这样极其强烈的日照变化，但是任何人都可以从这个新的研究中学到点东西，她说。
“今天24小时的生活方式对我们没有益处。如果人们都更注重自己的睡眠，公共的健康状况将会有所改善。”björkstén说。