Dementia and not blindness is the biggest contributor to disability in older people in low and middle-income countries, according to a study published in a disability special issue of The Lancet.
The conclusion contradicts global burden of disease estimates by the World Health Organization (WHO), which cite visual impairment (including blindness) as the largest contributor to disability in this part of the population in developing countries.
Researchers led by Renata Sousa of the Institute of Psychiatry, King’s College London and colleagues from the 10/66 Dementia Research Group studied this area because disability in older people in these countries has not been the subject of much research to date.
Numbers of older people are increasing particularly rapidly in these regions, from 490 million to 1.6 billion between 2010 and 2050, or from 9% to 20% of the total population.
Chronic diseases are also increasing, partly because of the process of demographic ageing and most chronic diseases occur more commonly in older people.
However, chronic disease risk factors such as smoking, unhealthy diets, and lack of physical activity, are also becoming more common due to urbanisation, industrialisation, and dietary and behavioural change.
The researchers looked at 15,022 people aged 65 years or older in 11 sites in seven countries with low and middle incomes – China, India, Cuba, Dominican Republic, Venezuela, Mexico, and Peru.
They assessed the contribution of physical, mental, and cognitive chronic diseases to disability, and the extent to which socio-demographic and health characteristics accounted for geographical variation in disability.
They worked out the proportion of disability that was due to each ailment, using the term the population-attributable prevalence fraction (PAPF).
The team found that in regions other than rural India and Venezuela, dementia made the largest contribution to disability – an average PAPF of 25%.
Other substantial contributors were stroke (11.4%), limb impairment (11%), arthritis (10%), depression (8%), eyesight problems (7%), and gastrointestinal impairments (7%). Associations with chronic diseases accounted for around two-thirds of prevalent disability.
The authors concluded: “On the basis of empirical research, dementia, not blindness, is overwhelmingly the most important independent contributor to disability for elderly people in countries with low and middle incomes.
“Chronic diseases of the brain and mind deserve increased prioritisation. Besides disability, they lead to dependency and present stressful, complex, long-term challenges to carers. Societal costs are enormous.”
In an accompanying comment in the journal, Dr Steven Sabat, Department of Psychology, Georgetown University, Washington, USA, said: “There is a tidal wave of social problems on the horizon in the lives of people in developing countries, because the incidence of dementia is growing and will continue to grow.”
DOI:10.1016/S0140-6736(09)62037-7
Lancet 2009; 374: 1821–30
