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Kristin Murphy, Deseret News
Harold Nielsen, 92, takes the dog leashes from his wife, Gloria, before taking Lexie and Missie for a walk at their home in Draper on Wednesday, Jan. 9, 2019.

DRAPER — Harold Nielsen has a few personal theories about what has kept him energetic and mentally sharp at 92 years old.

For one thing, he says, he and his wife are "very conscious of what we eat," with a longtime daily diet rich in "fish and vegetables and so forth" and devoid of cigarettes or alcohol. For another, he credits a heart attack he suffered when he was 40 for inspiring him to work "pretty hard at staying healthy" and in shape.

"Even today I work out three or four times a week," Nielsen said.

The Draper resident also cited the "incentives" he feels to "stay … to take care of my wife."

"A desire to live is important, too," Nielsen said.

Kristin Murphy, Deseret News
Harold Nielsen, 92, squeezes fresh lemon juice into a drink at his home in Draper on Wednesday, Jan. 9, 2019.

But ask him what he knows about whether his family tree may have played a part in his long life, and Nielsen, like many others, is at a loss. He feels there are conflicting examples among relatives — neither of his parents lived nearly as long as he has, though he has a sister who died at 94, and a healthy niece who is 91.

"I don't know about longevity in my family — it's really hard to say, all things considered," he said.

So to what extent is a person's longevity heritable from their family tree?

The answer to that question is not just an unknown curiosity for laypeople; it has long been coveted by researchers who study aging.

"It may be one of the oldest questions in the history of mankind ... what determines if we're going to live to these really exotic ages," explained Ken Smith, director of the Utah Population Database, in a recent phone interview.

University of Utah researchers now say they have new findings, published this week in the peer-reviewed journal Nature Communications, adding some clarity on the issue.

Kristin Murphy, Deseret News
Harold Nielsen, 92, walks his dogs Lexie and Missie near his home in Draper on Wednesday, Jan. 9, 2019.

The study concluded that "longevity is heritable, but that primarily applies to persons from families where multiple members are among the top 10 percent survivors of their birth cohort," said U. spokeswoman Brooke Adams. "The key to a long life can probably be found in the genes of these families."

Lead author Niels van den Berg, a professor in the Department of Biomedical Data Sciences at Leiden University Medical Center in the Netherlands, said by using a 10 percent threshold, "we observed … the more long-lived relatives you have, the lower your hazard of dying at any point in life."

"For example, someone whose parents are both 'top survivors' has a 31 percent lower hazard of dying than someone of the same age without such parents," van den Berg said in a statement. "Moreover, that person's hazard of dying is reduced, even if the parents themselves did not live to be extremely old but, aunts and uncles were among the top survivors."

The exhaustive project examined the genealogical trees of 314,819 people belonging to 20,360 families, drawing from records of people who lived as far back as 1740. Researchers used two large data sets — one based in the Netherlands, the other is the Utah Population Database.

“With these carefully constructed data sets, we observed the same family patterns of extreme longevity observed across diverse circumstances which demonstrate the value of deep genealogies for identifying specific families that potentially harbor genes for exceptional survival,” Smith said in a statement.

Kristin Murphy, Deseret News
Harold Nielsen, 92, shows some of the equipment in his home gym in Draper on Wednesday, Jan. 9, 2019.

Adams wrote that the results collected from Utah and the Netherlands were "similar … despite the very different environmental circumstances."

"In (the Netherlands), people stayed in the same place for a long time, while in Utah there was a high influx of migrants during the 19th century," Adams said. "Moreover, during the study period in Zeeland (Netherlands), there was a lack of clean drinking water, whereas in Utah fresh water was available from the mountains for some communities."

The high quality of the two population databases was considered extremely important for the strength of the study because "this field is filled with false signals of people claiming to live to (remarkable) ages, and often it is just bad record keeping," according to Smith, who is also a professor in the Department of Family and Consumer Studies and Population Sciences at the U.

Besides using two reliable population databases, there is also significant benefit to studying large extended families over multiple generations because it helps isolate genetic variables from environmental ones as much as possible, Smith said.

Kristin Murphy, Deseret News
Gloria Nielsen watches as her husband, Harold, 92, checks his blood pressure at his home in Draper on Wednesday, Jan. 9, 2019.

"Those distant relatives aren't likely to be your neighbor, or even live in the same town," he told the Deseret News.

When studying only close relatives, it is more likely those people would share similar environmental advantages or disadvantages, he said.

"There's a lot of environmental noise out there, and that's the challenge," Smith, a co-author of the study, told the Deseret News. "You have to be able to work through that."

The researchers concluded that studying a random group of subjects 100 years old or older is less effective in determining genetic factors for longevity in comparison to examining families where there are multiple relatives who were among the top 10 percent longest living people in their birth cohort.

That is an important finding in an area of study where researchers struggle to determine which family groups' longevity is actually remarkable enough to be worth studying, Smith said.

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Figuring out how to track genetic traits among those who live long lives has historically proved to be much more difficult than identifying traits linked to certain diseases, Smith cautioned. The difficulty in identifying responsible genes remains even when successfully identifying certain family groups with impressive longevity, he said.

"That is a very big question. There are private companies, there are lots of people trying to identify genes for longevity," he said. "The general view right now is that there are a lot of candidates in the literature, and it's probably not just one or two genes — it's probably a constellation of genes."