The global population is ageing as never before. Within the next five years, adults 65 and older will outnumber children younger than five; by 2050, they will outnumber children younger than 14.
Are we ready for this unprecedented demographic shift? We'd better be. The strains on health systems, governments, families and communities may be enormous.
The change will be particularly rapid in low- and middle-income countries, where most older people live and where their share of the population is growing fastest. For example, China's population aged 65 and older will double in less than 25 years to 14per cent of the total. It took France more than 100 years to reach that same point.
This is why the World Health Organisation has chosen ageing and health as the theme of this year's World Health Day today. As we consider the health implications of this phenomenon, it is crucial that we focus on adding life to years.
The road to healthy ageing begins before birth. An adult who was undernourished in the womb, or was obese as an adolescent, is at increased risk of disease. Fortunately, how we age depends on how we behave. By watching what we eat, being physically active and avoiding tobacco and the harmful use of alcohol, we can look forward to a healthier old age.
The conditions in which we are born, live, work and grow old also crucially influence how well we age. We need to ensure living conditions that enable us to stay healthy during our entire lifetimes.
The right to enjoy the highest attainable standard of health does not diminish with age, and a growing number of people will require age-friendly health systems that meet their needs - be they physical, social and mental. As more people than ever reach their 80s and 90s, there will be more people at risk of dementia. Many very old adults will require long-term community, residential or hospital care.
How well countries of the Western Pacific - which include China, Japan and the Philippines, among others - care for their ageing populations will depend largely on how well they tackle the corresponding increase of non-communicable diseases such as stroke, diabetes and cancer, as well as weak health systems and services.
Countries must deliver integrated services, covering the entire life course and including disease prevention, treatment, rehabilitation, palliation, long-term care and end-of-life care.
They must also eliminate discrimination in health care, so that treatable conditions of old age, such as hearing loss or musculoskeletal disorders, are not dismissed as a 'normal part of ageing'. In the rationing of scarce health resources, equity, not age, should be the determining factor. Health-care and social protection policies for older people must take into account the special needs of women, who outlive men on average but have lower rates of education, employment and well-being.
Older people have a lot to offer their communities - through paid or volunteer work, sharing their experience and knowledge, and helping to care for their families. But they can't do that if they're unhealthy. We need to reframe our concept of old age. We need to view it not as a time of inevitable decline, but one of active, meaningful and productive living.
We need to resist stereotypes that discourage older people from fully participating in society and prevent society from fully benefiting from their skills and experience.
Let us join hands on World Health Day to correct these stereotypes, support older people's efforts to contribute to society and develop age-friendly health systems. If we don't, we may find ourselves overwhelmed by the inevitable rise in the number of people with long-term disabilities and diseases that might have been avoided. We've no time to waste.
Dr Shin Young-soo is the WHO regional director for the Western Pacific