Alzhiemer's disease could affect twice as many people as the estimates suggest.

AIzhiemer's disease probably affects twice as many people as current estimates do not predict, but the victims have not yet presented symptoms, according to experts.

Scientists at the Mayo Clinic in Minnesota, have re-evaluated the prevalence of the disease using brain imaging to give a definitive answer to the number of people actually affected.

In Britain, about 850,000 people are said to have the disease, but most of them are diagnosed by clinical assessments when they already have symptoms.

However, tests conducted in a cohort study of 2,500 people showed that twice as many people were showing signs of protein plaques and tangles in the brain that are the hallmarks of the disease. Alzheimer's, although …