Jimmy Carter and his late wife, Rosalynn, were married for 77 years. A longevity expert says their relationship may have helped them live so long.

• Jimmy Carter is 99, while the average US life expectancy for men is 73.5.
• Carter's 77-year marriage could be a key to his long life, longevity expert Dan Buettner said.

Former US President Jimmy Carter says marrying his wife Rosalynn at 21 was the "best thing" he ever did.

Rosalynn, who died on Sunday at home after a brief period in hospice, was married to Carter for 77 years, making their union the longest between any presidential couple.

According to one longevity expert, the Carters' long marriage may be a key reason why Carter has lived for nearly a century, in relatively good health.

Carter, now 99, was with Rosalynn longer than any other president has been with their partner. Together, they share four children and 22 grandchildren. They resided at their modest family home in Plains, Georgia. Rosalynn, who died at 96, was recently diagnosed with dementia, the Carter Center announced in May.

The former president has 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 has 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 why marriage seems to have such great health benefits for those in them 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 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.