Lengthier smoking habits -- but not more intense ones -- seem to reduce the odds of developing Parkinson's disease, according to a study in Neurology. The inverse association between smoking and Parkinson's -- the neurodegenerative disease characterized by difficulty in controlling movement and speech -- was first reported half a century ago, but this is the first study to separate the number of years smoking from the number of cigarettes smoked per day. Researchers compared the smoking histories of 305,468 elderly subjects, 1,662 of whom had been diagnosed with the disease in the previousdecade. Compared to the nonsmokers, subjects who had smoked at least a pack a day for one to nine years were only 4% less likely to develop Parkinson's. But subjects who smoked as many cigarettes a day for more than 30 years had 41% shorter odds of developing the disease. The number of cigarettes a day, however, had no significant independent effect on Parkinson's risk. The results suggest that any Parkinson's-protective effects of tobacco reach saturation at low doses, the researchers said.

Caveat: It's possible that genetic factors determine both the propensity to smoke and protection from Parkinson's, rather than the smoke protecting against Parkinson's. Smokers may have remembered the duration of their habit more accurately than its intensity, which would skew the findings.

Jeremy Singer-vine

• movement [´mu:vmənt] n.活动；运动；动作 (初中词汇)
• previous [´pri:viəs] a.先，前，以前的 (初中词汇)
• tobacco [tə´bækəu] n.烟草(叶)；卷烟 (初中词汇)
• protection [prə´tekʃən] n.警戒；护照；通行证 (初中词汇)
• intense [in´tens] a.强烈的；紧张的 (高中词汇)
• decade [´dekeid] n.十年(间) (高中词汇)
• significant [sig´nifikənt] a.重要的；意义重大的 (高中词汇)
• intensity [in´tensiti] a.激烈；强度；深度 (高中词汇)
• elderly [´eldəli] a. 较老的，年长的 (四级词汇)
• accurately [´ækjuritli] ad.准确地；精密地 (四级词汇)
• duration [djuə´reiʃən] n.持久；持续期间 (六级词汇)