SINGAPORE - Centenarians in Singapore used to belong to an exclusive club, the lucky few who struck the genetic lottery for longevity.

In 1990, they numbered 50.

According to the Department of Statistics (DOS), there were 1,200 Singaporeans aged 100 and above as of last June, so the proportion of centenarians among Singaporeans has surged by 18 times between then and now.

Little is known about these 1,200 - who they are, what they did, and who looks after them now.

The DOS does not know who the oldest person in Singapore is.

What is known is that Singaporeans are living longer and healthier lives than people from most other countries. The World Health Organisation (WHO) ranked the Republic third in the world for average life expectancy last year, behind Japan and Switzerland.

Life expectancy was 83.1 years for Singapore, after Japan at 83.7 years, and Switzerland 83.4.

What's also impressive is that Singaporeans not only live longer than most, they also enjoy a greater span of good health. Singapore ranks second for healthy life expectancy, according to the WHO, at 73.9 years, behind Japan's 74.9 years, and ahead of South Korea's 73.2 years.

And that's not all. The rate of growth in average life expectancy is accelerating, the Ministry of Health said in 2016. Between 2003 and 2013, Singapore's total life expectancy rose by 3.3 years for the decade, compared with 2.8 years between 1990 and 2002.

What accounts for Singaporeans' longevity? Research is ongoing in what else plays a role, besides factors such as medical advances in disease treatment, and accessibility to good medical care.

Some of these fields are in:

Biology

Scientists from the Agency for Science, Technology and Research (A*Star) and the National University of Singapore have identified a type of immune cell that does not show signs of ageing. Such signs could be, for instance, the presence of certain genes or the shortening of structures on chromosomes usually associated with ageing.

Researchers hope to identify factors that cause them to resist ageing, which could one day lead to ways to harness that ability.

The study is part of the larger ongoing Singapore Longitudinal Ageing Study 2, which began in 2009 and involves 3,200 men and women aged 55 and above.

Gender

Though women tend on the whole to live longer than men, a study has found that Singaporean men appear to be healthier in old age than Singaporean women.

Could this be due to differences in education and family support or are there biological reasons?

Preliminary results of an ongoing study on longevity found Singaporean men were less likely to have impaired cognition (30 per cent, compared with 39 per cent in women) and more likely to be independent in their daily activities (47 per cent compared with 34 per cent in women).

More men had a positive outlook on their health, and were less depressed than women.

The SG90 Longevity Study is a 10-year study by A*Star and the National University

Health System (NUHS) involving about 1,500 Singaporeans aged 90 and above.

Education and ethnicity

A study by the Centre for Ageing Research and Education and published in 2016 found that

Singaporeans with secondary education or above had higher total life expectancy and active life expectancy at the age of 60 than those with primary education or below .

Data from a longitudinal survey of 4,990 Singaporeans aged 60 and above was used.

The findings suggest policies that increase education levels are a promising approach to increasing active life expectancy.

The impact on a country when its people live longer

When blessed with a population that enjoys a longer lifespan, a country has two key issues to consider.

First, will the greying of this population be accompanied by a longer period of good health, a sustained level of quality of life and extended periods of social engagement and productivity, or by more illness, disability and dependency?

Second, how will longer lifespans impact healthcare and social costs?

Prime Minister Lee Hsien Loong said at last year's National Day Rally: "On average, we live to 82 years and out of these 82 years in old age, we experience eight years of ill health."

Indeed, ageing expert Brian Kennedy, director of the Centre for Healthy Ageing at NUHS, notes that Singaporeans' "healthy life expectancy" has not increased in step with life expectancy.

He cited a 2012 global study which showed that, from 1990 to 2010, Singaporeans' lifespans grew by 5.4 for women and and six years for men, but healthspans grew by 3.4 and 4.1 years, respectively.

Professor Kennedy said the fact that healthy life expectancy is rising is a good sign. Still, the gap between healthspan and lifespan has to be stemmed or even decreased.

He suggests more research be done to delay ageing, which would delay the onset of chronic diseases such as diabetes and Alzheimer's, extend healthy life expectancy, and curb rising healthcare costs.

Prof Kennedy said the Centre for Healthy Ageing will look into whether ageing can be delayed through lifestyle modifications such as exercise and fasting, and through drugs. Studies will begin in the next six to 12 months.

Associate Professor of health policy and management at the Lee Kuan Yew School of Public Policy Phua Kai Hong argues that healthy life expectancy would increase naturally as demographics change.

"I would expect the average years spent in ill health to increase in the short term due to the low health literacy of the current cohort of elderly population," he said. This is due to "a lifetime of accumulated risk factors of unhealthy behaviours such as smoking, poor diet and lack of exercise, leading to chronic diseases".

"However, younger generations with higher health literacy are expected to have healthier life expectancies when they become old in the longer term," he added.

As for the second point, on the economic toll exacted, Finance Minister Heng Swee Keat said last December that Government expenditure on healthcare is expected to rise sharply because of the ageing population. "As medical technology improves, as our population ages, the demands will grow, and the need to provide for that will also grow," he said.

An Institute of Policy Studies study released last month said the ageing population would exert a drag on the growth of Singapore's gross domestic product per capita of 1.5 percentage points annually until 2060, assuming a stagnant fertility rate and stable immigration.

Professional services firm Marsh & McLennan Companies projects health expenditure on the elderly in Singapore to rise tenfold over the next 15 years to more than US$49 billion (S$65 billion) annually.

This means an average of US$37,427 will be spent on each elderly person by 2030, a rise from US$8,196 in 2015. This is the highest in the Asia-Pacific region.

"It's a conservative estimate as the numbers do not take into account indirect costs, such as transport, and opportunity costs from caregivers' time. It also assumes that we have the same ready access to cheap foreign labour, which may not be the case in the future," said Dr Jeremy Lim, a partner at Oliver Wyman global health practice.

Experts say policies and decisions on healthcare infrastructure spending need to be reviewed and individuals need to plan for their retirement healthcare needs.

Associate Professor Angelique Chan, executive director of the Centre for Ageing Research and Education, said the fastest-growing segment of the older population is those aged 80 and above.

"It is timely to start looking at the centenarians. Has disease onset been pushed to later in their lives? What are the frail and healthy predictors?" she asked, adding that research is lacking. "We are still a youth-centric country."