科學家稱夏天出生的孩子更陽光
Being born in the summer could give you a sunny disposition for life. And a winter birthday might cast a permanent shadow over your happiness, scientists believe.
Experiments suggest that season of birth dramatically affects the way the speed at which the body clock ticks.
A winter birth could leave it moving too slowly – affecting health and personality.
The intriguing theory comes from a study of mice exposed to varying amounts of light in the first months of life.
Some were given summer conditions of 16 hours of light and eight hours of darkness per day. Others had only eight hours of daily light, to mimic the short days of winter.
After they were weaned, they were kept in the same light cycle for several weeks or switched to the opposite one.
Finally, they were plunged into darkness and watched to see how they would react.
Those reared in summer conditions kept to a daily routine, but those brought up in little light struggled to cope with the change, the journal Nature Neuroscience reports.
Researcher Professor Douglas McMahon said: ‘The mice raised in the winter cycle show an exaggerated response to a change in season that is strikingly similar to that of human patients suffering from seasonal affective disorder.’
Despite this, the finding raises the intriguing possibility that the amount of light to which the human brain is exposed in the first weeks or months of life affects mood.
The professor said: ‘Our biological clocks measure the day length and change our behaviour according to the seasons.
‘Several studies show that people born in the winter months have an elevated risk of mood disorders such as seasonal depression, bipolar depression and schizophrenia – all of which are associated with disruption of normalcircadian rhythms.’
But being born in the summer can have drawbacks – such as an increased risk of short-sightedness.
Another study of more than 1.5 million children in the US clearly showed that those conceived in the summer are less clever than other youngsters.
It is thought that they receive more exposure to pesticides during the first few months of pregnancy – a critical time for brain development.
科學家認爲，出生在夏天將賦予你開朗的性情，而出生在冬天則可能給你的快樂蒙上永久的陰影。
實驗表明，出生的季節會極大地影響人體生物鐘運轉的速度。
冬天出生的人體內的生物鐘運轉得太慢，從而可能對健康和性格產生影響。
這一離奇有趣的理論來自一項對老鼠的研究，該研究把剛出生的老鼠暴露在不等量的光線下長達數月。
有些老鼠被放置在夏天的光照條件下，每天有16小時的“白天”和8個小時的“黑夜”。其他老鼠則只有8個小時的“白天”，和冬天晝短夜長的光照條件類似。
在這些老鼠斷奶後，他們被放置在相同的光照週期中長達數週，或轉換到相反的光照環境。
最後，科學家把它們都放置到黑暗中，觀察它們的反應。
根據《自然神經科學》雜誌的報道，那些在夏天的光照條件下成長起來的老鼠像往常一樣作息，而那些在缺少光線的環境中成長起來的老鼠在應對這一變化時卻顯得吃力。
研究者道格拉斯•麥克馬洪教授說：“在冬天的光照週期中成長起來的老鼠對於季節的變化表現出誇大的反應，這和得了季節性情感抑鬱症的人類病患的反應極其相似。”
此外，這一研究發現還提出了一個非常有趣的可能性，就是人的大腦在生命的最初幾周或幾個月所感知到的光照量可能會對心情造成影響。
教授說：“我們體內的生物鐘對白日的長短進行衡量，並根據季節變化而改變我們的行爲。
“幾項研究都表明，出生在冬天的人發生情緒異常的風險更大，他們更容易患上諸如季節性抑鬱症、兩極型憂鬱症和精神分裂症這種病，而這些病症都和打亂正常的晝夜節律有關。”
但是，出生在夏天也有不利之處，比如近視的風險會增大。
另外一項面向美國150多萬兒童的研究顯示，夏天受孕後生出的小孩不如其他小孩聰明。
據認爲，這是因爲這些小孩在孕期的頭幾個月接觸更多的殺蟲劑所致，而這幾個月正是大腦發育的關鍵時期。
Vocabulary:
sunny: cheerful and happy（歡樂的；快樂的）
intriguing: very interesting because of being unusual or not having an obvious answer（非常有趣的；引人入勝的；神祕的）
wean: to gradually stop feeding a baby or young animal with its mother's milk and start feeding it with solid food 使（嬰兒或動物幼崽）斷奶
circadian rhythm: 晝夜節律
