There are currently 800,000 people with dementia in the UK and 670,000 family and friends acting as primary carers, according to the latest estimates from the Alzheimer's Society.
The number of sufferers is estimated to rise to a million by 2021, and 1.7 million by 2051.
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The singer had been tweeting in support of migrants when she was bombarded with abusive messages.
Ministers are reportedly considering plans in a bid to lower inward migration.
In a tweet on Saturday, the US president didn't give a reason for his absence but said he wished"everyone well and have a great evening".