SALT LAKE CITY — Children who grow up without a father in the home have shorter telomeres, the protective chromosome caps that are believed to affect health and longevity, a new study says.

The findings are particularly troublesome for boys, whose telomeres were 40 percent more affected than girls' by the loss of their father.

The effect of father loss was most pronounced in children whose fathers died or were incarcerated before they turned 5, according to the study, published Tuesday in the medical journal Pediatrics. Nine-year-olds whose fathers are dead had a 16 percent reduction in telomere length, compared to children whose fathers are alive and living with their children.

Amid the bad news was a glimmer of good: The researchers found that a stable family income appears to mitigate the risk, most significantly for children of divorce. Income loss in the child's home after a divorce or separation accounts for 95 percent of telomere shortening, the study's authors said.

But shortened telomeres, which are seen by scientists as a kind of biological clock, are associated with a range of health conditions including obesity and mental illness. Some researchers believe shorter chromosome caps age us prematurely. A noticeable decline in telomere length among children who live without their fathers adds to evidence that shows the family structure matters not only in childhood, but throughout life.

The research "underscores the important role of fathers in the care and development of children and supplements evidence of the strong negative effects of parental incarceration," the authors said.

The specifics of the study

The children studied were among nearly 5,000 born between 1998 and 2000 who are part of the federally funded Fragile Families and Child Wellbeing Study.

Researchers interviewed mothers and fathers at the time of the children's birth and again when children were 1, 3, 5 and 9. When the children were 9 years old, researchers also collected samples of DNA through their saliva.

Telomere length is often calculated through cells in saliva since it's easy to collect, and telomere length is usually the same throughout the body, according to Elizabeth Blackburn, a Nobel Prize-winning researcher in telomeres who was not associated with this study.

"Telomere length is not the same for every cell type, but someone who is short for one category generally is shorter for the others," Blackburn has said.

In the new study on father loss and its effects on telomeres, researchers examined the DNA of 2,420 children from 20 U.S. cities. (Salt Lake City was not among them.)

Because of previous studies that found children's physical and emotional well-being are negatively affected by growing up without a father, the researchers suspected that telomere length might be adversely affected, too.

But Dr. Daniel Notterman, a study co-author and a senior scientist in Princeton University’s Department of Molecular Biology, told the Deseret News that he was surprised to find that the children's DNA was affected to the extent that it was.

Nine-year-olds who had no father in the home had telomeres that were 14 percent shorter than those with fathers. When broken down by reason for the loss of the father, the effect was greatest — 16 percent — in children whose fathers were dead. For children whose fathers were incarcerated, the reduction in telomeres averaged 10 percent; for those whose parents were divorced or separated, it was 6 percent.

The effects were greatest among boys and among those who had a genetic tendency toward anxiety, depression or pronounced sensitivity to their environment.

There were no differences by race or ethnicity, nor by the age at which the child lost his or her father. But financial stability of the household played a role in telomere length, most dramatically in homes of children whose parents were divorced or separated.

“I wouldn’t think of anything in this study as being too much good news, but it is a positive, at least for separation and divorce, that much of the problem seems to be related to loss of income,” Notterman said.

As to the reasons for the adverse outcomes, Notterman said the researchers could only speculate.

“We couldn’t test for these, but we have theories. Children need fathers; they’re very important. They play an economic role, but also provide love and attention, stability and cohesion, and they’re role models,” Notterman said.

When a father dies, the child suffers an irreplaceable loss, and having a father who is incarcerated adds to other problems that may be present in the family, such as poverty and racism, he said.

“It’s important for public policy makers to think of ways these adverse effects on these children can be mitigated,” Notterman said.

Why telomeres matter

Telomeres are at the forefront of research on health and aging, because their length helps to determine when cells in our bodies die.

They are tips on the ends of our chromosomes that act like a cap on a bicycle valve. They're composed of noncoding DNA, and each time a cell divides, they get smaller. When they get too small, the cell stops dividing and dies.

Chronic stress is known to be associated with telomere loss, and one study published in 2016 found shorter telomeres and accelerated cell aging in people who were separated or divorced.

Although the health of our telomeres appears to be affected by many things beyond our control — such as whether our father lives in our childhood home, or if our mother is stressed during pregnancy — there also are things we can do to help preserve them.

Eating a more healthful diet and getting more exercise and sleep appears to reduce the rate at which telomeres shrink, and could delay the onset of disease and increase our lifespan, some researchers say.

Blackburn, who in 2009 shared the Nobel Prize in Physiology and Medicine for work she and two other researchers did on telomeres, published a book earlier this year in which she advocates lifestyle changes to preserve telomeres. Among her suggestions: get seven hours of sleep, reduce sugar consumption and walk or jog for 45 minutes, three times a week.

"To an extent that has surprised us and the rest of the scientific community, telomeres do not simply carry out the commands issued by your genetic code," Blackburn and her co-author, Elissa Epel, wrote in "The Telomere Effect." "Your telomeres, as it turns out, are listening to you. They absorb the instructions you give them."