More than 45 million people around the world have dementia, the Alzheimer's Society says.

Alzheimer's disease is the most common cause of dementia. It can affect people of all ages, but usually it affects older people.

On World Alzheimer's Day, the Alzheimer's Society is urging leaders around the world to recognise dementia needs urgent action, and unite in ensuring better diagnosis, care and awareness.

This woman was living in a room in her family's home. It was kept locked due to her family's worry that she would get lost and "roam" around the village. It meant she was unable to speak or communicate to anyone.

Every day, the man in the foreground visits his lifelong friend in remote fishing village Mkwiro, even though his friend cannot remember him.

She is slowly losing her memory and because her daughters have to leave her for long periods, they worry about her "being lost in the bush".

Both these people are prominent figures in their local community. The man is considered a village elder. His wife cares for him, dressing him and remembering things for him throughout the day.

He is still treated with respect, although it is known he is having trouble with his memory.

Photographer Leah Beach who has traveled around Kenya, investigating the impact it can have.