My great-grandmother was a SuperAger who lived to 115 and was the second oldest person in Japan. Here's her advice for living a long and healthy life.

• Yumi Yamamoto is the great-granddaughter of Shigeyo Nakachi, who lived to 115 years old. 
• Yamamoto also works with Japanese SuperAgers as part of her job. 
• She shared the four habits that SuperAgers share. 

A longevity expert who speaks to SuperAgers every day, and whose great-grandmother lived until she was 115, shared advice for living a long, healthy life.

Yumi Yamamoto is the Japan research president at LongeviQuest, an organization that validates the ages of the world's oldest people and collects their stories. She is also the great-granddaughter of Shigeyo Nakachi, who, at the time of her death in 2021, was the second-oldest living person in Japan.

Yamamoto has collected lots of advice for living a long, healthy life from her great-grandmother and from speaking with Japanese supercentenarians every day. She shared some of her top tips with Business Insider.

1. Be consistent with habits

BI has previously reported on some of the healthy habits of the world's oldest people, including building exercise into their daily lives, and prioritizing community over work.

Yamamoto said that "most of the centenarians and supercentenarians I have met tend to have continued the same lifestyle habits throughout extended periods of time."

She said that it's the consistency of habits that help to extend longevity, "whether that's continuing to work after the age of 100 in some form, drinking a glass of sake every day, or climbing the stairs three or four times a day."

2. Have strict discipline

It helps to have good self-discipline when keeping a consistent routine, and Yamamoto said that this was a big part of her great-grandmother's life.

"My great-grandmother was very disciplined and very strict on herself. I think that her very ordered, very regimented lifestyle might have contributed to her longevity," she said.

She also said that this discipline extends to the eating and sleeping habits of many of the SuperAgers she speaks to.

"What I've noticed in these supercentenarians is that they're very disciplined and even strict on themselves in terms of the regimentation of their lifestyles. They don't do anything to excess, and that goes not just for food things and drink but also not staying up all night," she said.

3. Do everything in moderation

Although they're very disciplined, Yamamoto said that Japanese supercentenarians do allow themselves to indulge — just in a controlled way.

Where us "mere mortals" might not be able to resist eating a whole chocolate bar, she said, many supercentenarians would never eat the whole thing. This is helped by the Japanese practice of "hara hachi bu," a saying which instructs people to only eat until 80% full.

But, she also said that Japanese SuperAgers don't force themselves to do anything they don't want to do — "It is about having both balance and routine in life," she said.

Her great-grandmother, for example, while being very disciplined in other areas of life, refused to eat foods she didn't like. She hated fish, milk, yogurt, and dairy, so she didn't eat those foods, Yamamoto said.

4. Reduce stress

The last piece of advice that Yamamoto shared is something that many other supercentenarians and centenarians say: don't stress too much.

Yamamoto said: "Don't allow yourself to be in an environment which is too stressful or overwhelming."

She said that many supercentenarians try to "maintain a balanced state of mind and remain composed and dignified, sometimes in spite of the things that are going on around them."