手機使用率居高不下，為何腦癌發病率卻在下降？
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????上世紀80年代，隨著手機在美國投入使用，低頻率輻射開始影響人類大腦，腦癌發病率隨之緩慢上升。在80年代初，每年每百萬美國人中有63人被醫生診斷為腦癌，到1990年，這一數字上升到70人/百萬人。而此時手機使用才剛剛開始普及。 ????手機和腦癌發病率之間的相關性似乎肯定會呈上升趨勢，然而奇怪的是，從1991年開始，腦癌發病率突然調頭開始緩慢下降。2008年，即美國國家癌癥研究院（National Cancer Institute）有記錄的最后一年，每百萬美國人中只有65人患有腦癌。 ????在這20年里，隨著手機用戶數的瘋狂增長，美國人大腦所受到的手機輻射量增加了500倍。如今的美國手機用戶數比1990年時增加了大約60倍，平均每位用戶每天使用手機的時間也達到20分鐘，而在通訊費用昂貴的早期，這一數字還僅為一到兩分鐘。隨著用戶相互之間的通話時間越來越長，通話總時長也在迅速水漲船高。 ????以下圖表綜合了來自美國國家癌癥研究院和手機行業主要行業協會的數據，看起來頗為有趣。 |
????During the 1980s, just as Americans began pumping low-frequency radiation through their skulls with cell phones, brain cancer rates in the U.S. slowly increased. At the beginning of the decade, doctors delivered the devastating diagnosis of brain cancer to 63 out of every 1 million Americans every year; by 1990 that number had risen to 70 per million. And that's when cell phone usage really took off. ????Yet while the link between phones and tumors may have seemed certain to grow, a strange thing happened. Beginning in 1991 the rate of brain cancer incidence reversed course and began to slowly fall. By 2008, the last year for which the National Cancer Institute has data, 65 out of every 1 million Americans got a brain cancer diagnosis annually. ????During those same two decades, the radiation beamed by phones into American brains increased about 500-fold, in proportion to the wild growth in cell phone use. There are roughly 60 times more cell phones in the U.S. than there were in 1990, and each one is used for an average of about 20 minutes per day, up from just a minute or two in the industry's expensive early days. The combined effect of more customers each talking more has been a stunning increase in total talk time. ????Combining data from the National Cancer Institute and the cellular industry's main trade group yields this intriguing graph: |
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????布朗大學（Brown University）的傳染病科教授戴維?薩維茨曾進行過這類研究，他警告說，雖然從圖中能很清晰地看到手機輻射量與腦癌發病率之間沒有關系，但并不能完全證明手機是安全的。最令人擔憂的是，使用手機和最終罹患腦癌之間可能存在漫長的時間間隔。 ????不過塞維茨同時也認為，（低頻）輻射量大幅增加不會導致腦癌患者總人數上升這一發現是令人信服的。即便輻射暴露與罹患腦癌之間的平均時間間隔長達30年，但現實中必然會有在20年后就患病的特例者，這些人肯定會體現在目前的數據中。（情形與人們早期受到石棉等物質輻射，很長時間后才出現癥狀；類似。）雖然1990年時的手機用戶總數非常低，但也有足足500萬人。在2008年時哪怕這些早期使用者中只有很少一部分人染上因手機輻射導致的腦癌，那么當年的腦癌發病率也會出現大幅上升。 ????曾擔任過《美國流行病學雜志》（American Journal of Epidemiology）編輯一職的薩維茨表示：“真正的問題是，病情什么時候開始爆發？假如沒有跡象表明問題是何時開始發生的，那么相對于其它我們研究過的誘因，這次的情況可能將是史無前例的。” ????上周，世界衛生組織（World Health Organization）發布了一項研究報告，認定手機“可能致癌”，此結論主要基于一項研究發現：重度手機用戶罹患神經膠質瘤的風險增加了40%。據報道，這些用戶在10年里平均每天使用手機通話的時間超過30分鐘。對于典型的美國電話電報公司用戶（AT&T）而言，這個消息有點可怕。今年第一季度，他們的平均每天通話時間達到了21分鐘。而對于MetroPCS和Leap Wireless的用戶來說，這個消息簡直就是個噩耗。MetroPCS和Leap Wireless是專門從事替代固話服務的等廉價服務商。目前，Leap的語音用戶平均每天通話時間已經達到了驚人的50分鐘。 ????不過，至少到目前為止，所有重度用戶腦癌的整體發病率并沒有上升。 ????手機到底會不會導致腦癌？要得到這個問題的最終答案，我們還得等上幾十年時間，等到人們所接受的輻射量真正穩定在高水平，而腦癌發病率的趨勢出現明顯變化，要么掉頭上升，要么繼續下降。目前，輻射量已經開始趨于穩定。在經歷了30多年的高速發展后，美國用戶的手機通話時長在2010年時已經穩定在了每年2.7萬億分鐘的水平上。 ????譯者：項航 |
????The chart's clear disconnect between radiation dose and cancer rates does not conclusively prove cell phone are safe, cautions David Savitz, a Brown University epidemiology professor who has studied the issue. Most worrisome, it's possible there is simply a huge delay between a person using a cell phone and that exposure causing a brain tumor. ????Yet Savitz also finds the utter lack of an increase in total brain cancer following the massive increase in (low-level) radiation very reassuring. Even if the average lag between exposure and symptoms was 30 years, there would almost certainly be outliers who develop symptoms after just 20 years -- outliers who would be showing up in the data by now. (That's what's happened after early exposures to things like asbestos.) Total cell phone use may have been far lower in 1990, but there were already 5 million subscribers. It wouldn't take many of those early adopters coming down with cell phone-caused brain cancer to bump up the cancer rates in 2008. ????"The real question is: When would we see the beginning of the epidemic?" says Savitz, the former editor of the American Journal of Epidemiology. "It would be unprecedented relative to other agents we've studied to have no evidence of the beginning of the problem." ????The World Health Organization study released last week classified cell phones as "possibly carcinogenic to humans," based largely on a study that found a 40% increased risk for a cancer called gliomas among heavy cell phone users. Those users reported averaging 30 minutes per day talking on their phones over a 10‐year period. That's somewhat scary news for the typical AT&T (T) customer, who averaged 21 minutes a day in the first quarter of this year. And it's really scary for customers of low-cost providers that specialize in replacing landline service such as MetroPCS (PCS) or Leap Wireless (LEAP). Customers of Leap's Cricket service average a whopping 50 minutes per day. ????And yet, so far at least, all that talking hasn't jacked up the overall incidence of brain cancer. ????The ultimate answer to the question of whether cell phones cause brain cancer will only be definitively resolved after a few more decades in which the population's radiation dose stabilizes at a high level and brain cancer rates either jump or continue to decline. That stabilizing has already happened. After three decades of stunning growth, time spent talking on cell phones in the U.S. leveled off in 2010 at 2.7 trillion minutes a year. |
