Around 700,000 people currently suffer from dementia in the UK
Heavy drinkers and smokers develop Alzheimer's disease six to seven years earlier than those who do not smoke or drink, US researchers claim.
A study of 900 people aged over 60 found early onset was most likely in those who also had a high-risk gene.
A second US study found people with high cholesterol in their early 40s are one and a half times more likely to develop Alzheimer's.
The research was presented at an American Academy of Neurology meeting.
It has been estimated that a delay in the onset of Alzheimer's disease by five years would lead to a 50% drop in the number of cases.
The researchers said their findings showed heavy drinking and smoking were two of the most important preventable risk factors for the condition.
Those taking part in the study had been diagnosed with possible or probable Alzheimer's disease and smoking and drinking history was obtained from family members.
Heavy drinking, defined as more than two drinks a day was found to lead to an almost five-year earlier onset of Alzheimer's.
And those who smoked more than 20 cigarettes a day developed the disease two years sooner.
People with a specific gene - APOE variant 4 - developed Alzheimer's disease three years earlier than those without the gene variant.
All three risk factors together were associated with onset of the disease 8.5 years earlier than those with none of the risk factors.
Study leader, Dr Ranjan Duara, from Mount Sinai Medical Center in Florida said: "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."
In the second study, 9,700 men and women were followed from the age of 40.
Those with cholesterol levels higher than around six millimols per litre (mmol/L) had a one and a half times higher risk of developing Alzheimer's than those with low cholesterol.
"High mid-life cholesterol increased the risk of Alzheimer's disease regardless of diabetes, high blood pressure, obesity, smoking and late-life stroke," said researcher Alina Solomon.
Dr Susanne Sorensen, head of research at the Alzheimer's Society said the research added to the weight of evidence on drinking and smoking habits and the risk of developing dementia.
"The best way to reduce your risk is to eat a balanced diet rich in antioxidants and vitamins and to exercise regularly.
"Not smoking, drinking only in moderation and getting your blood pressure and cholesterol checked regularly throughout life are also important ways people can reduce their risk of dementia."