Dementia is the biggest health crisis facing our society today. 850,000 people in the UK have dementia - over 47million people live with the condition the world over.
Alzheimer's Society, for whom I'm an ambassador, are making great strides in helping communities across the world become more dementia aware. But there's a long way to go until society fully accepts what it actually means for a person to have dementia - and to think, act and talk about it in a way that means a person with dementia feels included and involved in their community.
My personal experience of dementia comes through my dear grandmother Nans. Nans has had dementia for about 15 years - and in that time I've seen a huge amount of change in her.
We've always been incredibly close. She was - and is - the warmest, most intelligent and gentle woman. She is the single most influential person in my life aside from my parents.
My earliest memories of Nans showing symptoms of dementia come from when I was about 16 years old. I remember her losing her way home on a short walk to the village, a walk she had taken hundreds of times before. I remember sitting down to a meal with her and watching her stare at her knife and fork having completely forgotten how to use them.
Today Nans rarely communicates verbally and most of the time her eyes are closed. Sometimes it feels like she's not there anymore and that we just can't reach her - and those are always the hardest visits.
However, she is very much still there and there is so much more to Nans than the dementia. For every visit that ends in tears of sadness, there are visits where we weep with joy.
One of the positives that has come out of our experience is being able to better see the world through the eyes of someone who is living with dementia. It has instilled in me a great desire to live in a society where people with dementia are understood and appreciated.
I'm passionate about promoting greater awareness and tackling stigma around dementia, To that end, Alzheimer's Society and the Department of Health recently asked me to be the UK's first ever Global Dementia Friends Ambassador.
The Dementia Friends initiative is doing amazing work in England and Wales. The biggest social action movement of its kind in the UK, there are 1.6million people signed up to take action and change the way people think, act and talk about dementia.
Yet dementia doesn't stop at UK borders and stigma is still rife in parts of the world.
In some countries, people with dementia are locked away or seen as being "mad". I've heard about people losing relationships, jobs and friends because of misconceptions that exist around the condition. I've raged on my sofa at comedy panel shows and TV sitcoms that have reduced a person with dementia to a poorly drawn caricature or the butt of a lazy joke.
At the moment, there's not nearly enough awareness around dementia and as a global society we have a duty to change that.
Being the UK's Global Dementia Friends Ambassador will enable me to inspire change the world over, as well as on our doorstep. From leading a Dementia Friends session for young people in LA to mark World Alzheimer's Day (today, 21 September) to meeting world leaders and encouraging them to take dementia stigma seriously, I'll be doing everything I can and working with the Alzheimer's Society as they roll their Dementia Friends programme out to countries across the world.
I've been asked many times what being a Dementia Friend - and undertaking this role - means to me. World Alzheimer's Day seems like a good chance to spell it out.
It means living in a society where people look out for others - where they are warm, friendly and helpful. It means everyone with dementia being treated with the respect and dignity they deserve, and not feeling ashamed or afraid. It means creating a world where every person in every corner of the world is dementia aware.
Carey Mulligan is Alzheimer's Society's Global Dementia Friends Ambassador and is tackling dementia stigma on an international scale. Find out more about becoming a Dementia Friend at www.dementiafriends.org.uk