April 21, 2000 --A new study may put to rest the notion that smoking offers
April 21, 2000 --A new study may put to rest the notion that smoking offers protection against Alzheimer's disease and similar brain disorders. Lead researcher Richard Doll, MD, tells WebMD that the results of this large-scale investigation "[contradict] what had been claimed in previous studies." The paper and an editorial in support of the findings appear in the April 22 issue of the British Medical Journal.
The study showed "no relationship whatsoever between smoking and the development of dementia," says Doll, who is a researcher and retired professor of medicine at Oxford University in England. When his team took a closer look at the earlier studies supporting such a link, they saw that "all of them had obtained information after people had developed dementia. But when we looked at the few studies in which smoking details were recorded before dementia was discovered, if anything, they showed that smoking caused rather than prevented dementia," he tells WebMD.
Beginning in 1951, Doll's team collected information at regular intervals on smoking and overall health in over 34,000 male British doctors. They analyzed data from about 475 of the men who'd died of or with dementia (smokers had picked up the habit at least 10 years prior to becoming ill). They compared the risk of developing dementia in long-term smokers with nonsmokers and those who'd quit smoking many years before death.
Overall, the odds of developing Alzheimer's were similar for smokers and nonsmokers.
These results may contradict earlier findings, but that doesn't mean the original hypothesis wasn't "perfectly plausible," Doll tells WebMD. "There's no question that smoking helps to protect against Parkinson's disease. The evidence is quite firm. It does diminish the risk of Parkinson's, so it was not implausible that it might diminish the risk of Alzheimer's, too," he says.
And Carol Brayne, MD, an epidemiologist with the Institute of Public Health in Cambridge, England, agrees. In her editorial, she writes that Alzheimer's affects pathways in the brain, which are also affected by nicotine. Because dementias involve the blood vessels in the brain, and smoking increases the risk of disease in blood vessels, it makes more sense that it could be a risk factor for dementia over the long term.
Doll tells WebMD that he expects there to be follow-up studies to verify the results and look more closely into how smoking and dementia are linked, but for the most part, "the issue is settled."
Brayne writes that "the public health message is clear: at the population level there is no protective effect of smoking in dementia."
Vital Information:
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- Contrary to previously held beliefs, smoking does not protect people from developing Alzheimer's disease.
- Nicotine acts on the same brain pathway as Alzheimer's disease.
- Smoking is known to protect against Parkinson's disease, and researchers had believed it could offer similar protection against Alzheimer's.
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