Published Monday, 11 June 2012
The This Is the Life hitmaker, 24, was left devastated as a teenager as she watched her gran's health and memory decline, and she's written Left That Body Long Ago to reach out to others affected by the condition.
Speaking on BBC Breakfast, Macdonald says: "My nana had Alzheimer's when I was at high school and she died over 10 years ago now and it was really hard to watch her because it was somebody you were so close to and you had such a good relationship with that no longer knew who you were.
"My mum would always make it easier for me by saying: 'Don't worry, that's not your nana, she's left that body and her mind's in a better place', and that would always make it better for me so I wanted to put that into words and maybe try and help other people that are going through the same thing."
The track is included on Macdonald's new album Life in a Beautiful Light.