Israel's Holocaust survivors tend to live longer, on average, than Israelis who were not exposed to the genocide, despite being in poorer health overall, according to new research published today by JAMA Network Open.

Survivors of the Holocaust have higher rates of several chronic health conditions than the general population in Israel , but live an average of seven years longer, the study found. Researchers say survivors' longevity may be owed to a genetic predisposition that helped keep them alive during the Holocaust, as well as a resiliency they gained as a result of the trauma.

"That's an enigma, to some extent," says Dr. Gideon Koren, author of the study and a senior investigator with the Kahn-Maccabi Institute of Research and Innovation, a medical research firm based in Tel Aviv. "How can you be sicker, but survive longer?"

Authors of the study say a combination of factors likely contribute to survivors' differing health outcomes, and that further research is needed to fully understand the results.

Researchers analyzed two decades of health data for nearly 39,000 Holocaust survivors who were born in Europe between 1911 and 1945, as well as about 35,000 people who were born in the future nation of Israel – at the time a territory under British rule – during the same years and served as the study's control group. All participants were insured by Maccabi Healthcare Services, an Israeli health plan with more than 2 million members.

The study found that rates of various chronic conditions – including bone fractures among women, as well as cancer, obesity, high blood pressure, coronary heart disease, heart attacks, chronic kidney disease and dementia among both men and women – were higher among Holocaust survivors than the general population.

For example, 83 percent of Holocaust survivors in the study had hypertension, compared with 66.7 percent of those who were born in Israel during the same time frame. Among survivors, 30.9 percent had chronic kidney disease, while 19.8 percent of the control group had the condition.

"After such a trauma, it's not surprising that people sustain a lot of damages," Koren says.

Yet survivors had a much lower overall death rate – 25.3 percent compared with 41.1 percent, as of the end of 2017. Among those who had died, survivors lived to an average of 84.8 years, while the control group lived to an average of 77.7 years.

"Israel has one of the highest life expectancies in the world," Koren says. "Because Holocaust survivors make up a large chunk of population – them and their children and grandkids – there must be some genetic aspect of resiliency."

Koren's study doesn't suggest survivors' genes were altered by their experiences – as does some contested research suggesting children of Holocaust survivors may inherit trauma through a form of epigenetic scarring – but researchers say it supports the hypothesis that survivors already had traits that helped keep them alive during the genocide.

"They're a selected group – very cruelly so, but a selected group that survived what most other people in the camps did not survive," Koren says. "They are very different people, genetically, emotionally, and many things we don't have a clue about, that are markers of resilience."

As a result of the trauma, those survivors who reached Israel may also have developed behaviors to resist their health problems, including coping skills, supportive social networks, optimism and a focus on health behaviors, the study said.

Researchers acknowledged a potential for bias in the results because survivors "may be more likely to seek medical help … owing to higher sensitivity to their health and better insight into health consequences," and may additionally be more likely to seek financial and other privileges.

The findings offer opportunities for further research, Koren says, particularly on the health outcomes and longevity of Holocaust survivors' children and grandchildren.