Journal of Alzheimers Disease & Parkinsonism
Open Access

Demographic ageing has been a much more rapid process in all world regions than anticipated, with the population aged 60 and over increasing at the fastest pace ever in developing countries. Globally, the numbers and proportion of older people are sharply increasing. The population in high income countries was aged 60 years or over is predicted to increase dramatically by 2050. This proportion in lowand middle-income countries (LMIC) was comparatively low but will be more than double by 2050. Chronic non-communicable diseases, which have been under-prioritized in the public health agenda for a long time, are now assuming a greater significance in LMIC.

Dementia has a disproportionate impact on dependency and disability and yet its global public health importance is still underappreciated. Co-morbid health conditions are particularly common among older people with physical conditions affecting different organ systems coexisting with mental and cognitive disorders. There is a general lack of awareness of Alzheimer's and other dementias as medical conditions. Dementia is under-recognized, even in high-income countries. This under-recognition seems to be accentuated in LMIC, where they are commonly perceived as a normal part of ageing. Lack of awareness directly affects help-seeking behavior and hence the recognition and management of the condition, which in tum contribute to the burden experienced by the family and other main carers of people with dementia.

Alzheimer's disease International (ADI), the umbrella organization for national Alzheimer's associations (AA), has been collating evidence on the global prevalence of dementia, the projected increases over time and its impact worldwide. It has convened a panel of experts to review the global evidence on the prevalence, numbers of people affected and its impact.

Since the global evidence-base has expanded considerably. There have been new studies from Europe and the United States, and an explosion of dementia prevalence studies from LMIC and other regions and groups previously under-represented in the literature. The most recent study update used a new systematic review of the prevalence of dementia and found it to be significantly higher than previous studies. As more data becomes available, the variation in prevalence between world regions is reduced.

The most recent available estimates for the global incidence of dementia show the incidence of dementia increased exponentially with increasing age. For all the studies combined, the incidence of dementia doubled with every 5.9-year increase in age. Estimates of the global The most recent available estimates for the global incidence of dementia show the incidence of dementia increased exponentially with increasing age. For all the studies combined, the incidence of dementia doubled with every 5.9-year increase in age. Estimates of the global annual numbers of new cases increased and then declined with increasing age in each region. Worldwide, millions of new cases of dementia are anticipated each year, implying one new case every 4.1 seconds.

The number of people worldwide affected by dementia provides one indicator of the impact of the disease, without fully capturing the problem for the individual affected, their families and society. The impact of dementia can be understood at three levels: (1) The person with dementia, who experiences ill health, disability, impaired quality of life and reduced life expectancy; (2) The family and friends of the person with dementia, who in all world regions, provide the cornerstone of care and support for the person with dementia; (3) Wider society, health and long-term care systems and lost productivity.

Dementia is one of the main causes of disability in later life, but it is important to understand the contribution of dementia, relative to that of other chronic diseases. They are highly influential in terms of prioritization for policymaking and planning at national, regional and international levels. The key indicator is the disability-adjusted life year (DALY), a single integrated measure of disease burden calculated as the sum of years lived with disability (YLD) and years of life lost (YLL).

All current projections of the scale of the coming dementia epidemic, including those published by ADI, assume that the age and gender specific prevalence of dementia will not vary over time, and that population aging alone dives the projected increases.

The basis for this assumption is uncertain, since prevalence is a product of incidence and survival with dementia, and a fall in either or both of these indicators would lead to a fall in age-specific prevalence. A decline in age-specific incidence, at least in high-income countries, was theoretically possible, driven by changes in exposure to suspected developmental, lifestyle and cardiovascular risk factors for dementia. The strongest evidence for possible causal associations with dementia was those of low education in early life, hypertension in midlife, and smoking and diabetes across the life course. However, the prevalence of obesity and diabetes has been increasing in most developed countries. The trends in cardiovascular health among older people in many low- and particularly middle-income countries are in an adverse direction, with a pattern of increasing stroke and ischaemic heart disease morbidity and mortality, linked to an epidemic of obesity, and increasing blood pressure levels.