夏はコーヒー微糖と無糖紅茶２０００ｍｌを２～３日で飲んでいる。そのためか夜一度起きると朝方まで寝れないこともある。幸せ病の１種であろうか。ロシアの炭鉱夫のオバちゃん方に睡眠障害などあり得ない！
circadiana.blogspot.jp/2006/01/persistence-in-perfusion
thepaleomom.com/2014/02/regulating-circadian-rhythm
下記研究ではメラトニンリズムへのカフェイン影響が論じられている。
heidimatchembiol4550.blogspot.jp/2008/09/assignment-1-my-favourite-hormone
夜のコーヒーに体内時計乱す作用、米研究
ＡＦＰ＝時事 9月17日(木)10時7分配信 headlines.yahoo.co.jp【AFP＝時事】
寝る前にコーヒーを飲むと、予定の就寝時間に眠りにつくのが難しくなり、朝起きるのがさらに辛くなるのは、カフェインによって体内時計が乱されるからだとする研究結果が16日、発表された。
米研究チームが米医学誌「サイエンス・トランスレーショナル・メディシン（Science Translational Medicine）」に発表した研究については、カフェインを含む飲料を夜に飲むことで就寝と起床が遅くなる理由を説明するだけでなく、将来的には、時差ぼけの影響を抑える目的でカフェインを使用するのに適したタイミングについてのヒントをたらす可能性もある。
研究は、被験者5人を対象に行われ、それぞれに、就寝3時間前にダブル・エスプレッソの含有量に相当するカフェインを摂取させる、明るい光にさらす、プラセボ（偽薬）を与えるといったタスクを無作為で与えた。
被験者をさまざまな条件下に置いて調査するこの実験は49日間にわたり実施された。その間、被験者の唾液を定期的に検査し、睡眠と覚醒の周期を自然に調節するホルモン「メラトニン」の濃度を調べた。
論文によると、低光量の条件下でカフェインを摂取させた被験者は、約
「40分間のメラトニン概日（24時間周期）のリズムの位相後退（遅い時間へのずれ）」
を経験したことが、今回の実験で分かったという。
他方、就寝3時間前に明るい天井照明にさらされた被験者では、体内時計に85分間の遅れ、またカフェイン摂取と明るい光の両方の条件下に置かれた被験者は、体内時計に105分間の乱れが生じた。
米コロラド大学ボルダー校（University of Colorado at Boulder）のケネス・ライト（Kenneth Wright）教授は「世界で最も広く使われている向精神薬のカフェインが、人間の体内時計に影響を与えることを示したのは、今回の研究が初めてだ」と語り、また
「この研究は、カフェインが人間の生理機能に及ぼす影響に関する最新の興味深い知見をもたらすものだ」
と続けた。
今回の研究結果は、寝る前のカフェイン摂取は避けるようにとの一般的なアドバイスの説得力を高める一方で、カフェイン適切な使用が時差ぼけを回避するために体内時計をリセットする一助となり得る「興味深い」可能性を秘めたものと論文は述べている。
だが、日付変更線を横断する旅行者が眠らずに活動を続けるための、カフェインの最も効果的な利用方法を決定するには、さらなる研究を重ねる必要がある。
「このような条件下でカフェインが誘発する睡眠の乱れについては、時差ぼけを悪化させる恐れがあり、経過の観察が重要になる」
と論文は指摘している。
【翻訳編集】 AFPBB News
Drinking coffee late at night can throw your internal clock out of sync
looknews.org/news/148777/drinking-coffee-late-at-night-can-throw-your-internal-clock-out-of-sync
Drinking coffee before bed may delay the human circadian rhythm by up to 40 minutes — making it more difficult to go to sleep at night, according to research published today in Science Translational Medicine.
It's the first research to show caffeine to have a direct effect on a person's internal timekeeping system. And coffee can even throw off your sleep cycle on evenings following a late-night caffeine boost, the study suggests.
It’s estimated that more than half of American adults over the age of 18 drink coffee every single day. And these coffee drinkers are consuming an average of three cups daily. Numerous studies have examined the effects of coffee’s impacts on the body, due to its high concentration of caffeine.
"Caffeine is one of the most widely consumed drugs that’s legal, but is also has these psychoactive impacts,"
says study author Dr. Tina Burke, a neuroscientist at the University of Colorado at Boulder.
However, its effect on our biological clock and internal rhythm hasn’t been well understood.
doctorsgates.blogspot.jp/2010/09/melatonin-and-its-uses
The circadian clock is a biological system that sends cues to your body telling you when you should be awake and when you should be asleep. It's controlled by a region of the brain that regulates hormonal and neural activities that trigger certain bodily functions — like sleepiness and alertness — over a 24-hour period. The circadian clock takes cues from a person's environment — that’s why, for instance, your jet lag isn’t permanent. Several things affect these rhythms but
"the biggest training cue is light; it's the primary synchronizer for the day,"
says Burke.
The clock isn't the only thing that makes you sleepy, though. There's also the homeostatic sleep-wake system, which causes the buildup of a chemical called adenosine. Adenosine inhibits processes that make you feel awake. Caffeine blocks the chemical, making you feel more alert.
But Burke and her team wanted to see if caffeine also affects the body's circadian clock, too. So Burke set up two different experiments. The first involved analyzing a group of five volunteers over a 49-day period.
The participants took a caffeine pill — equal to the amount of caffeine found in two shots of espresso — every night three hours before bed. This group was compared to people who were exposed to light before bed; it’s well known that too much light can delay a person’s sleep cycle at night. Overall, the caffeine group had their internal rhythms thrown off by 40 minutes — about half the time delay experienced by those who were exposed to light at night.
foodandnutritionresearch.net/index.php/fnr/article/view/17252/23292
Then, Burke turned to human cell cultures. The researchers exposed cells associated with the circadian clock to high levels of caffeine in the lab. The caffeine prevented the circadian cells from signaling that it was time for sleep.
The research implies that coffee is doing more than just keeping you alert at night. It could be putting your entire rhythm out of sync. That means drinking coffee one night might have effects on your sleep cycle for many nights to come.
"You find it difficult to go to sleep at your standard desired time,"
said Dr. Timothy Roehrs, a researcher of sleep medicine at Henry Ford Hospital in Detroit, who was not involved in the study. Roehrs said this would cause people to be phase delayed, meaning it's difficult to go to sleep during your standard desired time.
"If you’re usually going to bed at 11 o’clock, it’s now midnight."
It's also possible that late-night coffee drinking is contributing to sleep issues, such as circadian sleep-wake disorders — where people can't sleep and wake up during the times the want. Because of this, Burke says people need to be much more considerate of the times they drink caffeine.
io9.com/5646561/how-do-you-really-know-what-time-it-is
Though the study links caffeine to changes in the circadian clock, Roehrs said the cellular effects in the lab may not explain the sleep delays seen in the human subjects.
"It would be very difficult to figure out,"
he said. However, he said it makes sense that the drug is directly altering the biological clock.
"Here they are showing the inherent characteristics of the cells are being changed,"
Roehrs said.
"It’s a more direct demonstration than what has been seen before."