?生物谷報(bào)道：美國科學(xué)家最新研究顯示，晚上開燈睡覺或熬夜是導(dǎo)致女性患乳腺癌的主要因素之一,。此報(bào)道也是基于先前數(shù)年的研究結(jié)果,。由美國國家癌癥研究所和美國國家環(huán)境衛(wèi)生科學(xué)研究所共同進(jìn)行的研究，為非自然光與癌癥之間的關(guān)系提供了“首份證據(jù)”,。
報(bào)道說,，大量研究表明那些需要值夜班的職業(yè)婦女，如護(hù)士,、空中乘務(wù)員,，她們患乳腺癌的風(fēng)險(xiǎn)最高可達(dá)60％。此外還有研究表明,，每周熬夜2到3天的女性也同樣易患乳腺癌,。
研究人員認(rèn)為，夜間的燈光妨礙了褪黑素（Melatonin）的生成,，而褪黑激素在抑制癌細(xì)胞生長的同時(shí)也會(huì)增強(qiáng)免疫系統(tǒng),。當(dāng)前研究表明，Melatonin與多種癌癥的形成均有關(guān)系,，如乳腺癌,，皮膚癌等。
在最近的研究中,，研究人員將乳腺癌的腫塊移植到老鼠身上,，并給這些老鼠分別注入取自清晨或夜間經(jīng)電燈照射之后的老鼠血液,。研究發(fā)現(xiàn)清晨（也就是睡眠之后）的血液使癌細(xì)胞的生長速度減緩了80％，而電燈照過的血液加速了癌細(xì)胞的生長,。
專家建議,，睡覺時(shí)關(guān)閉所有電燈，因?yàn)樗谌诘姆块g中有利于制造神經(jīng)傳遞物質(zhì)血清素,，這對(duì)制造褪黑激素至關(guān)重要,；盡量保持9小時(shí)睡眠；早上起床后到戶外走走,。
The nighttime hormone melatonin puts breast cancer cells to sleep. It also slows breast cancer growth by 70%.
David E. Blask, MD, PhD, of Bassett Research Institute in Cooperstown, N.Y., reported the findings at this week's annual meeting of the American Association for Cancer Research.
Breast cancers get revved up by a kind of dietary fat called linoleic acid. Melatonin interacts with linoleic acid, so he gave melatonin to mice implanted with human breast cancers.
"This breast cancer rev-up mechanism gets revved down by melatonin," Blask said at a news conference. "Nighttime melatonin is a relevant anticancer signal to human breast cancers. Ninety percent of human breast cancers have specific receptors for this signal."
The hormone seeps from a pea-sized gland in the brain when the lights go out at night. It's the reason you get sleepy when it's dark. Blask and colleagues found that melatonin puts cancer cells to sleep, too.
Blask's team exposed lab mice with human breast cancers to constant light. Tumor growth skyrocketed.
"With constant light, tumors grow seven times faster and soak up incredible amounts of linoleic acid," he says. "During the day, the cancer cells are awake and linoleic acid stimulates their growth. But at night cancer cells go to sleep. When we turn on lights at night for a long time, we suppress melatonin and revert back to the daytime condition."
The finding may explain why nurses who often work the night shift have high rates of breast and colon cancer.
Blask says clinical trials are under way to see whether melatonin supplements can help treat cancer. It may also help in other ways.
"When you take melatonin prior to normal onset of sleep, it will [jump-start the sleep cycle]," he notes. "Many cancer patients suffer from sleep problems. Melatonin may also improve the quality of life in cancer patients by helping them sleep."
Arizona Cancer Center researcher David Alberts, MD, notes that there is a lot of interest in melatonin as a sleep inducer. However, he worries about the safety of over-the-counter melatonin supplements.
"The issue is safe dosing of melatonin," he said at the AACR news conference.
Provided that melatonin supplements actually contain the hormone, Blask isn't worried about overdose.
"In human studies, melatonin has basically no toxicity," he tells WebMD. "Now it takes very little melatonin to stimulate nighttime sleepiness -- on the order of three-tenths of a milligram. But you can't overdose with melatonin. People have taken gram quantities. Its nastiest side effect is sleepiness."
