This urban population is leading the world in life expectancy

The result is a healthy, long-lived population boasting the highest life expectancy in the world.

Narrowly beating residents of Japan and other "blue zones" such as Italy, men in Hong Kong are living, on average, up to 81.3 years and women even longer, 87.3 years, as of 2016. "Over the last few decades, (Hong Kong) has caught up in a big way," said Dr. Timothy Kwok, professor of geriatric medicine at the Chinese University of Hong Kong.

Dr. Gabriel Leung, dean of the faculty of medicine at Hong Kong University, noted that "we inched past Japan about five years ago. It's not a position that we've found ourselves in for decades."

As Hong Kong is not a country, it is not included in the Global AgeWatch Index, a measure of social and economic well-being in 96 countries, developed by HelpAge International. But Kwok's research team used the same criteria as the index, combined with other factors, to reveal just what's helping the population live longer.

It begins with their environment.

According to Kwok's research, "Hong Kong ranks first for enabling environments," he said. "That may explain our longevity."

The streets are safe, and there is easy access to public transport, healthy food and public amenities, "enabling" people to live a healthier lifestyle.

The temptation to get in a car and drive is minimized by footbridges and elevators that provide easier access to walking routes and affordable taxis and public transportation: A ride on the clean, air-conditioned metro starts at just 60 US cents.

"You can easily walk to your nearest shops or shopping center ... to what you need," Kwok said. "Older people especially don't go to the supermarket; they go to open markets."

"We are greener than most cities," Kwok said, adding that in many green spaces, it's common to see groups of elderly people doing tai chi or qi gong calisthenics in the early hours, after which they spend time together to share meals and converse.

"Tai chi morning exercises are very popular and play a role," Leung said, but his team is studying just how big a role these factors play in life expectancy.

"We need to be designing urban spaces to facilitate that kind of activity," said Dr. John Beard, director of the department of aging and life course at the World Health Organization.

Almost all the districts of Hong Kong are members of the WHO global network of age-friendly cities, which encourages the creation of urban spaces supportive of older people, Beard said. This includes positive images of older people, active leisure and programs for spiritual well-being.

The government also ran an initiative in which older people were invited to go around and identify problems with footpaths and other barriers to mobility, after which officials took note of the issues and addressed them in their plans, he explained.

"Anyone can get to hospital," Kwok said, adding that Hong Kong has universal heath care for hospital treatment but not quite universal for primary care.

"The negative is that people go to (the emergency room) far too often," he said. However, older people generally do not pay for primary care and get priority.

"When you're sick, really sick and need to be hospitalized, it's free at the point of care, paid for by taxation," Leung said. "Nobody would be denied adequate medical care due to lack of means."

Beard agreed that accessible health care contributes to longevity, as fewer people might die from conditions that would otherwise have killed them.

"It's important that access is for everybody, not just the rich," Beard said. "That's when the average life expectancy will increase, as you won't have those people at the bottom who influence the average in a negative way."

Leung stressed that good health care in the earlier years of life, not just the later ones, is just as important when determining life expectancy.

This means maternal, neonatal and childhood care to prevent childhood diseases as well as efforts to prevent "the big killers" of middle age such as cancer, heart disease and stroke, he said. "These two drivers determine a population's life expectancy at birth."

Leung estimates that 70% of Hong Kong residents over the age of 70 were born in mainland China and came over in search of better opportunities.

"A lot of them came as economic migrants ... and were almost triathletes," he said. "They climbed, they ran, and they swam." Migrants also need to be psychologically fitter than their peers to have the motivation to uproot their lives.

"Physically, you need to be fit to endure the journey," he said. "These are the people who are meant to be at the highest risk of dying now, at the rate of their peers back in their village, but they're not dying."

This survival advantage, combined with improved childhood health care, is what Leung believes drove Hong Kong's "life expectancy miracle."

Kwok also believes that Hong Kong is well-positioned geographically, with a subtropical climate that has a part to play.

"It's not too hot and not too cold," making life easier and more comfortable, he said.

In countries such as the UK, there are more deaths during the winter months: For example, there were an estimated 34,300 excess deaths during the winter of 2016-17. In the US, there were an estimated 108,500 excess winter deaths in 2008.

However, other parts of the world renowned for their healthy elderly populations have cooler or scorching environments at times, said Leung, who believes that this factor has less of a role in longevity.

"Japan has a very different climate than Hong Kong, and Singapore has a very different climate to Japan," Leung said. "We are subtropical, Singapore is tropical, and Japan is temperate.

"These things play a role, but they can't be the main driver."

Another geographical benefit is "access to good food," Kwok said.

Hong Kong's position as both a marine and land gateway to China and other parts of Asia enables greater access to fresh fish, fruit and vegetables, he said. Combined with a cuisine that includes them in most dishes, the population as a whole eats well.

"We studied the Chinese diet, and it's quite similar to the Mediterranean diet," he said, with meals often consisting of fish, fruits and vegetables, rice, nut oils for cooking and meat chopped up into dishes rather than eaten as whole portions.

"We mix it up," he said.

Beard said, however, that when highlighting factors such as diet -- whether in Hong Kong, the Mediterranean or Japan -- it's important to note that people have always eaten this way. "So why are they living longer now?" he asked. "There were probably also reduced stressors."

The close familial networks of Asian cultures in general is well-known, providing both financial and social support as people get older.

"Older people tended to have a lot of children," Kwok said. But with decreasing family sizes and China still recovering from a one-child policy, that is likely to change for the next generation of older people. "Baby boomers had less children."

Beard adds, however, that the Asian philosophy of a filial piety -- a virtue of respect for one's parents, elders and ancestors -- is pivotal to the happiness seen in older age, both physical and psychological.

"Older people are genuinely respected, and younger members of the family put an emphasis on ensuring the well-being of older members of the family." said Beard.

"Confucian culture," said Leung. "But we shouldn't talk this up."

He highlights Tokyo, Hong Kong and Singapore as some of the most densely packed places on Earth, where "it's hard to fit a two-, three-generation family in the same household."

However, Beard believes people are adapting. "The mechanisms are now changing, but there are innovative ways people are exploring, such as video connections and cash transfers, to enable this filial piety to continue," he said.

The experts agree that a country ranking at the top for life expectancy does not mean there's no room for improvement -- far from it.

The Global AgeWatch Index also explored social care elements, such as mental health and income security, which Kwok believes is not Hong Kong's strong point when it comes to the elderly.

"Participation in civil society is not as strong as Western countries," he said, citing employment and volunteering among older people and highlighting that mental health is not prioritized as part of health care, with people often waiting years for a referral to a specialist.

Suicide rates in Hong Kong are highest among people over the age of 65. Of 937 suicides recorded in 2014, 241 were by people over that age, according to the HKJC Centre for Suicide Research and Prevention at Hong Kong University.

It's also estimated that one in three elderly people there has depressive symptoms.

"We want people to live happily for longer, not just live," he said.

Kwok highlighted that Hong Kong does not have a government pension system, with people instead relying on their children. "We do badly in income security," he said.

Leung agreed: "There is a lot of work we should do to make sure these people live healthily and happily."

Most changes at the top of the longevity list are marginal, Beard said. Japan and Hong Kong "are ... world leaders, along with Germany, Italy and Australia."

Leung agrees. "It is not a given that life expectancy only goes up," he said, highlighting the United States, where life expectancy has fallen in recent years.

Changing diets and pollution are likely to affect patterns seen in recent years, Beard said. "Diets are not as healthy as they have previously been ... and we need to do what we can to help people live longer, healthier lives. It's never too late"

Leung's study aims to determine the biggest factors driving high life expectancy in Hong Kong and just how big a role they play. The researchers are testing their core hypotheses that this is because of universal health care, improved childhood care, economic migration and reduced smoking rates among women compared with other parts of the wold, resulting in fewer smoking-related diseases.

If these are found to be underlying factors, he hopes to use that information to inform policy measures to maintain a healthy, long-living population and keep Hong Kong at the top.