And they put it down to lower rates of heart disease, which results from people living more healthily and keeping fit and active.
A balanced diet, being careful about weight, stopping smoking and keeping blood pressure normal have been shown to bolster the brain.
Studies have found risk factors for heart disease in middle age speed up decline of brain function in older adults. They also showed medicines such as statins and aspirin taken for heart conditions could be key to slashing dementia rates.
The latest research from Sweden - published in the journal Neurology - offers hope that drugs with a proven safety record could be used to stave off and treat the brain disease.
Patients could routinely be given them to protect long-term against Alzheimer's.
Chengxuan Qiu of the Ageing Research Centre, established by the Karolinska Institute and Stockholm University, said that health check-ups and cardiovascular disease prevention have improved significantly, and they now see results of this improvement reflected in the risk of developing dementia.
But the centre's director Laura Fratiglioni warned that the reduction of dementia risk is a positive phenomenon, but it is important to remember that the number of people with dementia will continue to rise along with the increase in life expectancy.