Jimmy Carter and his wife, Rosalynn, were married for 77 years. Their relationship may have helped them live so long.

• Jimmy Carter has died at 100: the average life expectancy for men in the US is 73.5.
• Carter's 77-year marriage could have been key to his long life, longevity expert Dan Buettner said.
• Research suggests married people, especially men, live longer than their unmarried counterparts.

Former President Jimmy Carter, who died at age 100 on Sunday, said marrying his wife Rosalynn at age 21 was the "best thing" he ever did.

The couple were married for 77 years before Rosalynn died at age 96 last year — making their union the longest of any presidential couple. Rosalynn was diagnosed with dementia months before her death.

Together, they shared four children and 22 grandchildren. They resided at their modest family home in Plains, Georgia.

The former president surpassed the average US male life expectancy of 73.5 by more than 20 years, and his committed, loving relationship could have played a major role in his longevity, research suggests.

Marriage can have serious health benefits — especially for men

When researchers looked at the life expectancy and marital statuses of 164,597 Americans over age 65, they found that married men and women lived, on average, two years longer than their unmarried counterparts.

Even marriages that end can have a beneficial effect on our longevity. People who were divorced or widowed also tended to live longer than those who had never been married, according to the same 2020 study. (Important caveat: Unhappy marriages in which partners constantly criticize one another or are too demanding and controlling can erase these health benefits.)

Experts say the reasons marriage has great health benefits are numerous and complex, and the exact reasons why are still poorly understood. But there does seem to be something protective about the social bonds and support that a healthy union can provide, with more built-in opportunities to socialize and connect.

What we do know is that the health benefits of marriage seem to be greater for men than for women. Another study, published in March 2023, found that bachelors with heart failure were twice as likely to die within five years, compared to married men with the same heart issues.

Decades of other research point to similar findings. Being married can decrease a person's risk of heart disease, cancer, and other life-shortening health conditions like hypertension and high cholesterol.

Author and longevity expert Dan Buettner, the man who pioneered the idea that there are five "Blue Zones" for centenarians, told Business Insider that "investing in a spouse is a core value in all Blue Zones," whether a couple lives in Okinawa, Ikaria, Nicoya, Loma Linda, or Sardinia.

"Staying in a committed relationship is absolutely associated with about two years of extra life expectancy (and more for men) over being divorced or single," Buettner said.

It's a key part of the way that some of the world's longest lived people connect with their tribe, and put their loved ones first, reducing inflammation in the body, promoting healthy behaviors, and keeping loneliness in check.