A large study suggests, heavy smokers with a 40-a-day habit face a much higher risk of two common forms of dementia. The risk of Alzheimer's is more than doubled in people smoking at least two packs of cigarettes a day in their mid-life. The risk of vascular dementia, linked to problems in blood vessels supplying the brain, also rose significantly. The study showed among those currently smoking two or more packs, equivalent to 40 or more cigarettes a day, there was a 157 per cent increase in the risk of Alzheimer's disease. There was also a 172 per cent increase in vascular dementia risk compared to someone who had never smoked. The US study, looking at over 21,000 people's records, is published in the journal Archives of Internal Medicine. The link between smoking and Alzheimer's has already been suggested – but this is one of the biggest studies looking at how smoking in mid-life affects dementia risk decades later.