How did Henry Kissinger live to 100? He had no idea.

• Henry Kissinger has died at the age of 100, but he had no idea how he lived so long.
• Genetics can play a big role in longevity, and both Kissinger's parents lived to their 90s.
• Maintaining social connections and having a strong routine are also thought to help. 

Henry Kissinger, the legendary statesman who helped shape modern geopolitics, is dead at 100.

He seems to have been as surprised as anybody that he made it that far.

In his last TV interview, with Axel Springer CEO Mathias Döpfner , the two touched briefly on the point.

"How I lived to be 100? I don't know. I didn't aim for it," Kissinger told Döpfner.

Kind of unsatisfying if you want to be 100, too!

But it gets worse — according to his family, Kissinger did many things that doctors will tell you not to.

His son, David Kissinger, wrote about his father's lifestyle and longevity for The Washington Post earlier this year.

He noted that his father had "a diet heavy on bratwurst and Wiener schnitzel, a career of relentlessly stressful decision-making, and a love of sports purely as a spectator, never a participant."

So — a poor diet, high stress, and no exercise.

Instead, per Kissinger Jnr., it was all in the mind. His father, he wrote, had "unquenchable curiosity" and a "sense of mission."

Despite his frailty, Kissinger stayed part of world events until almost the end — he made public appearances in China and Washington DC even after his 100th birthday.

Someone else agrees with that — the former Google CEO Eric Schmidt co-wrote a book on AI with Kissinger which was published in 2022.

Speaking about his co-author, he said Kissinger never stopped working, and theorized that it kept him alive.

"He works harder than a 40 year old," said Schmidt. "I can tell you that he gets up in the morning and he works all day. He has dinner with his wife and his family and he works at night."

He concluded: "I am convinced that the secret to longevity is being a workaholic."

Routines, social connections, and genetics play a role in longevity

Many so-called "SuperAgers" — people over the age of 80 who retain certain cognitive abilities, such as good memory, which are similar to people in their 50s — don't necessarily follow what we might consider healthy lifestyles, a longevity researcher previously told Business Insider's Hilary Brueck.

While many lifestyle factors associated with health, such as keeping active, managing stress, following a balanced diet, and not smoking, are linked to longevity, research suggests that there are equally if not more important factors that are sometimes overlooked.

Having strong social connections, for example. Older people who were visited by family and friends once a month were found to live longer than those who had fewer visits, a recent study by researchers at the University of Glasgow, UK found.

Having a daily routine and habits — known as "routineology" — has also been linked to living longer, even if those habits aren't the healthiest.

"The content of our days is not as important for longevity as doing things regularly to support stability," Dr. Angel Iscovich wrote in his book "The Art of Routine: Discover How Routineology Can Transform Your Life" after interviewing centenarians.

Genetics play a big role in how long a person lives too.

"Good genetics are a wonderful thing," Dawn Skelton, a professor of aging and health at Glasgow Caledonian University in Scotland, UK, told BI.

Living to 99 or 100 is not as unusual as it used to be, but it's rare for people to do so without embedding physical activity into their lives, she said.

According to Thomas Perls, director of BU's New England Centenarian Study, reaching the age of 90 is about 30% genetics and 70% lifestyle, reaching the age of 110 is roughly 70% genetics.

With Kissinger's parents having lived to the ages of 95 and 97, it's likely his genetics played a role in his longevity.

Ultimately, however, it's a bit of a mystery why some people live to their late 90s or 100s without seemingly trying to.