By Jen Christensen and Val Willingham
(CNN) -- It is Her Majesty's custom to send a personal greeting to her subjects on their 100th birthdays. These days the Queen of England has a lot more letters to write.
That's because a record number of people are living to 100 and beyond in the United Kingdom -- and worldwide. In fact, one-third of babies born in the UK in 2013 are expected to live to 100, according to their Office of National Statistics. In the United States, the population has seen similar trends.
As this centenarian population grows, scientists want a better understanding of how and why those people do eventually die.
A new study finds that these 100+ types are more likely to have "old age" listed as their cause of death than chronic diseases, according to lead author Dr. Catherine Evans.
The study, published in the most recent edition of PLOS Medicine, finds that most centenarians die from pneumonia or general frailty rather than cancer or heart disease. Chronic diseases are more likely to kill people who only make it to their 80s and 90s.
To get at this information, Evans examined data from the death records of people in the United Kingdom who died between 2001 and 2010. She looked at a group of 35,867 people who were between 100 and 115 when they died. The median age of death was 101.
Evans said she was surprised at how large that 100+ population is. It has nearly doubled every decade since the 1950s in the UK. Globally the 100+ population is projected to grow to about 18 million people by the end of the century.
Looking at where these centenarians died showed that the majority ended their days in a care home (61%) or hospital (27%). They were less likely to die at home (10%) or in hospice care (0.2%).
Earlier studies show the elderly prefer to die at home, so the study authors argue that as this population grows there is an "urgent need to ensure adequate long-term care and responsive community care services to support people living with extreme longevity in these care settings."
Since the elderly are often frail, earlier studies have shown that "home" isn't necessarily about the brick and mortar where a person's family lived. Home, Evans suggests, may be more of a "metaphor for where you feel safe and secure, and where your loved ones are nearby."
While this study specifically looked at the British population, the number of centenarians has grown all around the world.
Dr. Ronald D. Adelman, who works with many of these old-old people as the medical director of Cornell's Wright Center on Aging, said that the study is an important tool to understand a population that's often overlooked.
"When it comes to the elderly there are really three groups we look at," explained Adelman. "Those who are considered old, who are 65 to 74 years of age; the older, between ages 75 to 84; and the old-old, which are those people over the age of 85.
"But when you look at centenarians, that really is an expanding group, and the important thing is to get their advance directives, to make sure these people express how they want to be treated in their later years, so they can live a better quality of life and be more comfortable. Where do they want to live, how do they want to live and what's best for them?"
Because of advances made in medical technology, and the fact many people entering their golden years are more health-conscious than ever before, Adelman says it's time society takes the elderly, including centenarians, seriously because this older age group will continue to grow and need care.
"To be honest, 65 is no longer old," noted Adelman. "Ten thousand Americans are turning 65 every day. There are 77 million baby boomers, who were born between 1946 and 1964. They are more educated, they have the best health literacy than prior generations, they exercise, they eat right and they are living longer, healthier lives.
"We need to be able to provide them the best care and services possible, as they age into their 80s, 90s and beyond."
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