Carey Mulligan has spoken about the potential impact of dementia on patients' families and her own 91-year-old grandmother, who suffers from the disease.The Oscar-nominated actor, who is an ambassador for the Alzheimer’s Society, urged the families of dementia sufferers to continue to visit their relatives even if they no longer recognise them. Mulligan said her grandmother "Nans" hasn't recognised her or the rest of her family for seven years.Speaking on a special episode of BBC Radio 4's Today programme, which she guest-edited, the star of An Education, The Great Gatsby and Suffragette said the visiting of dementia patients by loved ones can have a calming effect, regardless of how much their illness has developed.Mulligan said there have been some "terrible terrible moments" during visits to her grandmother, who is living in a care home in Wales and rarely speaks, but there have also been "moments of real joy" and laughter, reported The Telegraph “It gets so awful and we’ve had terrible visits where we’ve all ended up in tears, and then there are the visits where something really magical happens.”Mulligan said that while "she won’t remember that we’ve been there... the sensation of being in company of someone who loves you is something we can’t deny.“There’s a calmness, there’s a companionship: these really fundamental feelings of being loved, being taken care of by people and family who really love you, I think that’s something that regardless of how progressed your dementia is stays with you."Mulligan, who has spoken publicly about her grandmother's condition before, is campaigning to raise awareness and help change global attitudes towards dementia.Writing for BBC Magazine , she said that while the growing prevalence of the disease has improved how society views dementia, "There is still a long way to go and the stigma of dementia remains rife".Around 850,000 people in the U.K. have the condition and more than 47 million people live with it around the world.Yet still, she added: "Too many common myths and misconceptions about dementia still exist. Time and again I hear reference to it as just being a natural part of ageing. And, unfortunately, it is often the butt of distasteful jokes."But dementia is a disease of the brain and it requires understanding, care and support."