Heavy drinkers and smokers develop Alzheimer's disease up to eight years earlier than those with healthier lifestyles, research has shown.

A junk food diet which causes high cholesterol levels in middle age also leads to a higher risk of the disease, say scientists.

The lifestyle links to Alzheimer’s were revealed today in two separate studies presented to neurologists in the US.

One team looked at 938 Alzheimer's patients aged 60 and above. The researchers asked family members about the patients’ drinking and smoking history, and found that heavy drinkers - those who consumed more than two alcoholic drinks a day - developed Alzheimer’s nearly five years earlier on average than non-heavy drinkers.

Smokers who got through at least 20 cigarettes a day developed the disease 2.3 years sooner than patients who smoked less or were non-smokers.

Participants with a particular mutant form of the gene ApoE showed symptoms of Alzheimer’s three years earlier than those without the gene variant.

Adding the three risk factors together led to considerably earlier onset of the disease, with patients with all three developing Alzheimer’s 8.5 years sooner than those with none.

The 17 patients in the study with all three risk factors began to experience Alzheimer’s at an average age of 68.5 years, whereas 374 participants who had none of the risk factors developed Alzheimer’s at an average age of 77.

“These results are significant because it’s possible that if we can reduce or eliminate heavy smoking and drinking, we could substantially delay the onset of Alzheimer’s disease for people and reduce the number of people who have Alzheimer’s at any point in time," said Dr Ranjan Duara, the study leader, from the Wien Centre for Alzheimer’s Disease at Mount Sinai Medical Centre, Miami Beach, Florida.

“It has been projected that a delay in the onset of the disease by five years would lead to a nearly 50 per cent reduction in the total number of Alzheimer’s cases.

"In this study, we found that the combination of heavy drinking and heavy smoking reduced the age of onset of Alzheimer’s disease by six to seven years, making these two factors among the most important preventable risk factors for Alzheimer’s disease.”

Dr Duara presented his findings at the American Academy of Neurology’s annual meeting in Chicago.

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