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【Science News——编译】日光——抗肿瘤药物？S
日光——抗肿瘤药物？
看看你防晒霜的说明，很明显，过多的在日光下暴露会导致皮肤癌。然而最近的两项研究提供了明确的证据显示，对某些种类的皮肤癌日光事实上是一种保护作用。
现在已知日光中的紫外线（UV）辐射会导致DNA的突变，进而导致皮肤癌的发生。然而已有证据表明日光照射同样也是有益的。例如，在穿透大气的紫外线较少的地方，乳腺癌、前列腺癌和直肠癌的死亡率要高。实验室研究发现，紫外线照射后皮肤内合成的维生素D对许多类型的细胞具有抗肿瘤作用。“所有的结果都显示经过日光照射对肿瘤的发生有保护作用或者能降低肿瘤的死亡率，”田纳西州纳什维尔Vanderbilt大学医学中心的Kathleen Egan说。
在2月2 日出版的Journal of the National Cancer Institute上，两个研究组提供了支持上述结论的证据。由瑞典斯德哥尔摩Karolinska研究所流行病学家Karin Ekstrom领衔的研究组研究了日光暴露对淋巴瘤的影响，和皮肤癌一样，这种肿瘤在过去的十年中变得非常普遍。他们调查了3740位诊断为恶性淋巴瘤的患者，同时调查了3187名健康对照者。研究发现健康人中假期进行日光浴的要多与病例组，甚至他们要晒得比淋巴瘤患者要黑。这一数据提示，接受日光的照射能降低淋巴瘤患病率30%-40%。“这不是个小数字，”Ekstrom Smedby说。
由新墨西哥州大学的流行病学家Marianne Berwick领衔的另一项研究则调查了日光照射对黑色素瘤的作用，这是一种最严重的皮肤癌。在调查了528名诊断为该病的患者病随访了五年之后，研究人员发现日光照射较多的这种病的患者的死亡率仅有日光照射较少患者的一半。研究组认为，维生素D的增加可能是这一现象的原因，而另外一种解释是日光照射可以促进DNA的修复，从而减少黑色素瘤的侵袭。
这两个研究组都警告他们的研究需要进一步重复。黑色素瘤患者和有皮肤癌家族史的人对于照射日观仍需谨慎，Egan说，因为更大的威胁来自于黑色素瘤。但是这两项研究都支持维生素D的保护作用。“日光可能不再是肿瘤中的一个负面因素，”他说。
--ERIK STOKSTAD
原文：
http://sciencenow.sciencemag.org/cgi/content/full/2005/202/1?etoc
OR http://bric.postech.ac.kr/biotrend/science/science_view.php?nNum=95769&nPageNum=4&nType_id=3&szSearchKey=&nCategory_id=-1&nDateOrder=&nHitOrder=&nRecoOrder=
Sunlight - Cancer Drug? 2005-02-03
Read the back of your tanning lotion, and the implication is clear: Excessive sun exposure can lead to skin cancer. Two new studies, however, provide evidence that sunlight may actually help fight some kinds of cancer.
Ultraviolet (UV) radiation in sunlight is known to mutate DNA and can lead to skin cancer. Yet circumstantial evidence has been building that sun exposure can also be beneficial. For example, mortality from breast, prostate, and colon cancer tends to be more severe at higher latitudes, where less UV penetrates the atmosphere. Lab studies have also shown that vitamin D--synthesized in the skin after UV exposure--has anticancer effects on many kinds of cells. "All the arrows pointed to something about past sun exposure that was protective or had a beneficial effect on [cancer] mortality," says Kathleen Egan of Vanderbilt University Medical Center in Nashville, Tennessee.
In the 2 February issue of the Journal of the National Cancer Institute, two groups present supporting evidence. A team led by epidemiologist Karin Ekström Smedby of the Karolinska Institute in Stockholm, Sweden, looked at the role of sun exposure in lymphoma, which, like skin cancer, has become more common over the past few decades. They interviewed 3740 patients diagnosed with malignant lymphomas and 3187 healthy controls. Those without the disease reported more sunbathing, vacations to sunny destinations, and even more sunburns than did patients with lymphoma. The data indicate that sun exposure can lower the risk of lymphoma by 30% to 40%. "It's not a small reduction," says Ekström Smedby.
The other study, led by epidemiologist Marianne Berwick of the University of New Mexico, examined the role of sun exposure in melanoma, the most serious kind of skin cancer. After interviewing 528 patients diagnosed with the disease and following their health for 5 years, researchers discovered that those with a history of more sun exposure were half as likely to die from melanoma than those who had had less sun exposure. One reason could be the benefits from increased vitamin D production, the team speculates, but another possible explanation is that sun exposure stimulates DNA repair, leading to less aggressive melanomas.
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作者:admin@医学,生命科学 2011-06-03 17:14
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