In 2010, China had more people living with Alzheimer’s disease than any other country in the world – and twice as many cases of Alzheimer’s and other kinds of dementia as the World Health Organization thought.

Cases of all kinds of age-related dementia in the country rose from 3.7 million in 1990 to 9.2 million in 2010. This is the finding of the first comprehensive analysis of Chinese epidemiological research, made possible by the recent digitisation of Chinese-language research papers. Previous estimates, based on English-language papers, seem to have under-reported the number of cases by half.

“We are now only beginning to comprehend the enormous value in this ‘parallel universe’ of information,” says Igor Rutan of the University of Edinburgh, UK, who was part of the team that carried out the research.

The figures are bad news for a country where 90 per cent of the elderly must be cared for by their families – old people who still have family members living are not allowed to be admitted to a nursing home – even as widespread migration to cities has disrupted the traditional family structure.

Population bulge
The findings are a reflection of China’s ageing population, and its policies.

As countries modernise, death rates fall, and later on birth rates fall as more people take up birth control. Between the two events, though, there is a “bulge” of births, the source of the modern world’s population explosion. Eventually birth and death rates roughly equalise, but the birth bulge remains as an age bulge in the population.

This reached an extreme in China, where a surge in births in the 1950s and 1960s was followed by plummeting birth rates in the 1970s, later reinforced by China’s one-child policy. “Family planning policy means China is becoming an ageing country much faster than other middle-income countries such as India,” says co-author Wei Wang of Edith Cowan University in Perth, Australia.

In its youth, the bulge underpinned China’s economic development. But by 2033, it is predicted that working-age people will be outnumbered by dependents, mostly the elderly.

The new research shows that they will need more care than China was expecting. Dementia rises in an ageing population: cases increased from 4.9 to 6.3 million in the greying European Union between 2004 and 2010.

Unhealthy lifestyle

“The rates in China are similar or even higher than rates in Europe and the US,” says Wang.

And they are rising. In 1990, the team estimates, 1.8 per cent of Chinese aged 65 to 69, and 42.1 per cent aged 95 to 99, had dementia. In 2010 those figures were 2.6 and 60.5 per cent, respectively. If similar rates hold in other middle-income countries, there might be 20 per cent more cases of Alzheimer’s worldwide – five million more – than now estimated, the authors calculate.

The increase in China might reflect better diagnosis, but an urbanising lifestyle could also be causing more dementia. “Obesity, diabetes and suboptimal health contribute,” says Wang.

Martin Prince of King’s College London, who is organising another survey for dementia in China, says that if midlife obesity is a risk factor for dementia, then future rates in China could be 20 per cent higher than estimated.

Journal reference: The Lancet, doi.org/msp

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by Debora MacKenzie