By Quentin Sommerville
BBC News, Shanghai
Liu Faxiu is 80 years old and, as she sits in a cold corner of her unheated nursing home, she has vivid memories of the Japanese occupation of Shanghai half a century earlier.
Prof Xiao says China's Alzheimer's problem is growing quickly
"I came to Shanghai in my teens with my parents. We came to the city as refugees during the fighting with Japan, we made military uniforms," she said.
But more recent memories are difficult for her to grasp. She is uncertain where she lives now, or how long she has been there.
That is because she is one of China's six million sufferers of Alzheimer's. The country now has a third of all Alzheimer's patients in the world. And the number of diagnosed cases is rising.
China's economic success means people are living longer, says Professor Xiao Shifu, a director at Shanghai's leading mental health hospital.
"Alzheimer's prevalence has been about what you'd expect in the west. But now it's increasing very fast because China is ageing at a very rapid rate," he said.
And the enormous changes in society are taking their toll, especially on the old.
"We're seeing more cases of depression among old people - especially among those who live alone and have no one to talk to. And depression is a risk factor for Alzheimer's," he said.
Spotting the symptoms of the disease is becoming more difficult, as China's traditional community support networks are being eroded.
Da Zhongli is a traditional Shanghai neighbourhood. It sits off the city's main shopping street, Nanjing Lu, and its crowded community of old-style houses has long been noisy and full of life.
Mr Wei worries about his games of Mahjong
But the neighbourhood has grown quiet. It is scheduled for demolition.
Seventy-three-year-old Mr Wei still lives there, playing Mahjong with his neighbours. But most people have moved out and it is getting difficult to find enough people to play a game.
"We don't want to leave our neighbourhood, we'll have nowhere to play Mahjong. In high-rise flats people keep themselves to themselves, in houses like this one we're always in and out of each others' homes," he said.
Shu Haolun, a documentary filmmaker who grew up in Da Zhongli in his grandmother's home, has been filming the changes in the community.
"If somewhere has an earthquake, the whole community is gone, you just wiped everything out. But (with this) it's man-made, not from nature," he said.
During the Cultural Revolution, 30 people were living in his grandmother's house. But she died last year and most of the other residents have taken the government's compensation and moved to the city's outskirts. Now only three people still live in the house.
"My grandmother was worried about moving to a new place. She didn't know how to live in a new place without her old friends, the environment. You know during the day maybe some neighbours bring some food and play Mahjong. My grandmother really liked this place," he said.
Early diagnosis is critical to the treatment of Alzheimer's, but there is a great deal of ignorance about it. In Chinese it is called "idiot's disease".
As part of China's market reforms, the country's healthcare system has been privatised. Hospitals have been overwhelmed, according to Professor Xiao.
"There aren't enough medical facilities equipped to treat Alzheimer's patients, even in Shanghai. But if you go into the rural areas in the west and central china, it's even worse and patients can't be sure of proper diagnosis and treatment," he said.
Healthcare - which was once free in China - is now expensive.
There is a greater risk of Alzheimer's, and the break-up of traditional communities means it is more difficult to spot early.
China's pensioners understand that, increasingly, they have to look after themselves.