賓夕法尼亞大學(xué)（University of Pennsylvania）行為睡眠醫(yī)學(xué)項(xiàng)目副主任菲利普?格曼認(rèn)為，通常人們在夏天會感到更愉快。我們的晝夜節(jié)律（包括睡眠周期、荷爾蒙波動和體溫，大致以24小時(shí)為一個(gè)周期）主要受日光影響。格曼說：“人們在夏季的幾個(gè)月里會感覺更好，心理狀態(tài)有小小的提升，會有更多的正面情緒?！?/p>

但實(shí)際情況也不是千人一律。波士頓大學(xué)（Boston University）神經(jīng)科學(xué)教授伊琳娜?V?日達(dá)諾娃博士說：“晝夜節(jié)律因人而異，所以日照的多少和時(shí)長對不同的人來說意義也不同?！北热纾绯康年柟鈺屃?xí)慣晚醒的人感到不適。而對于習(xí)慣早起的人來說，早晨的陽光就會有積極的效果，傍晚的陽光倒是會讓他們不高興。

日達(dá)諾娃認(rèn)為，這一點(diǎn)與飲食習(xí)慣類似。

她說： “有的人喜歡一日三餐，有的人喜歡一日十餐（每一餐的分量都較?。Ｔ谝惶熘械哪硞€(gè)時(shí)段，對于有些人來說陽光是很好的興奮劑，但對另一些人來說，陽光不僅不能給人帶來正面情緒或者起到提神的效果，反而還會引起輕微的不快。”

更多的日照還能控制晝夜節(jié)律，在這個(gè)過程中，人體生物鐘可以根據(jù)體外的環(huán)境（比如自然的明暗周期）來進(jìn)行自我調(diào)節(jié)。日達(dá)諾娃認(rèn)為，由于白晝變長，人體晝夜節(jié)律通常會得到更好的控制，也就是說能夠更好地與自然光線的明暗變化保持一致，而后者影響著人們的睡眠質(zhì)量與情緒。

但是格曼也表示，目前還不太清楚更為愉悅的情緒狀態(tài)到底是來自更佳的晝夜節(jié)律和睡眠質(zhì)量，還是只跟日照有關(guān)。

布萊根婦女醫(yī)院（Brigham and Women’s Hospital）醫(yī)學(xué)生物鐘項(xiàng)目主任弗蘭克?謝爾認(rèn)為，反過來看，冬天的日照較少確實(shí)會帶來一些問題。他說：“日照時(shí)間的延長或縮短確實(shí)會有顯著的影響。冬天，白晝變短，很有可能我們醒來時(shí)天還黑著。此時(shí)，晝夜節(jié)律系統(tǒng)還沒開始促使我們清醒并調(diào)整情緒?！?/p>

所以，在白晝最長的夏至日前后，盡情享受日光吧。白晝正在慢慢變短哦!（財(cái)富中文網(wǎng)）

?

譯者：劉偉義

In general, people are more cheerful in the summertime, according to Philip Gehrman, associate director of the Behavioral Sleep Medicine Program at the University of Pennsylvania. Light serves as the strongest cue to regulate circadian rhythms, which include the sleep cycle, hormonal fluctuations and body temperature and follow a roughly 24-hour pattern. “People tend to feel better in summer months,” Gehrman said. “There’s a slight elevation in our mood. More positive emotions are reported.”

But the effect isn’t uniform—circadian rhythms vary from person to person, so the amount and timing of sunlight means different things to different people, said Dr. Irina V. Zhdanova, a neuroscience professor at Boston University. For example, morning sunlight can irritate people who wake up late. On the other hand, for people who rise early, morning sunlight can have a positive effect, but sunlight may irritate them in the evening.

It’s similar to meal habits, Zhdanova said.

“Some like three meals a day, others like 10 small meals a day,” Zhdanova said. “Sometimes sunlight is good and uplifting during a certain time of the day, while for others, it’s neither uplifting or positive and can induce mild irritation.”

The extra sunlight also entrains the circadian rhythm, a process in which the internal biological clock aligns itself to external cues, like the light-dark cycle. Now that the days are longer, in general, the circadian rhythm is entrained much better, Zhdanova said. In other words, the circadian rhythm is better aligned with natural sunlight and darkness, which can affect people’s sleep and moods.

However, Gehrman said, it is unclear whether elevated moods come from more entrained circadian rhythms and better sleep, or if the happiness boost is directly attributable to the sunlight.

On the flip side, experiencing less sunlight in the winter can pose a challenge, said Frank Scheer, director of the Medical Chronobiology Program at Brigham and Women’s Hospital.

“The lengthening or shortening of the light period during the day does have a clear effect,” Scheer said. “In wintertime, when the days are shorter, we are more likely to wake up when it’s still dark outside and before the circadian system stimulates wakefulness and improved mood.”

So, enjoy the longest day of the year while it lasts—the days will start getting shorter again from here.