Remembering to brush your teeth properly every day into old age could help fight dementia, scientists claim.
Evidence is mounting that Alzheimer's can be fuelled by the bacteria that cause gum disease.
The bugs are thought to affect brain functions such as memory - so good oral hygiene could lower the risk of developing dementia, say experts.
In the latest research, British researchers found that Alzheimer's patients declined six times faster if they had bad gums.
Conversely, they say improving oral hygiene in dementia patients could even slow their decline. It could prove a crucial breakthrough because there are few pills for the disease despite hundreds of drug trials. The researchers, from King's College London and the University of Southampton, tracked the health of 59 men and women with Alzheimer's for six months. The memory of 20 who had gum disease declined more rapidly than the others, the journal PLOS ONE reports.
Tests revealed that their blood had a higher level of chemicals that cause an inflammatory response that can damage the brain.
Gum disease affects 80 per cent of Britons aged 55 and over. Around half of those aged 65-plus have also lost more than ten teeth - a sign of severe gum disease. Mark Ide, of King's College London, said treating gum disease in those who already have Alzheimer's might slow their decline.
And regular tooth-brushing may help prevent the disease in healthy adults. But he said 'most people are rubbish' at cleaning their teeth.
"We think it is better to do it really thoroughly once a day, having been instructed how by your dentist, than do it badly once a day," he said.
Previous research found that those who brushed their teeth once a day are 65 per cent more likely to develop dementia than those who brushed three times a day.
Dr Doug Brown, of the Alzheimer's Society, said: "This study adds evidence to the idea that gum disease could potentially be a contributing factor to Alzheimer's but we would need to see clinical trials to provide more solid evidence."