Study: Heavy smokers double Alzheimer's risk

Researchers in Finland, Sweden and at Kaiser Permanente in Oakland followed more than 21,000 middle-aged people who smoked two packs a day for more than 20 years.

The heavy smokers had a 157 percent higher risk of developing Alzheimer's and a 172 percent higher risk of developing vascular dementia -- another common form of dementia.

Researchers think smoking could cause dementia by narrowing blood vessels in the brain.

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