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WEDNESDAY, June 11, 2003 (HealthDayNews) -- Identical twins who share tight emotional ties along with their genes may be boosting their life spans, researchers report.
But such close bonds don't appear to do anything to extend the lives of fraternal twins, says study author Malcolm D. Zaretsky, a research biologist at the University of California at Berkeley.
"My feeling is that there's something in the relationship that's established early on" between identical twins, Zaretsky says. "Having a strong relationship with others contributes to better health."
While studying heredity and longevity, Zaretsky became curious about why identical twins tend to live longer than fraternal twins.
"My imagination suddenly started wondering about that. I wanted to look into what could possibly be the differences between these two," he says. "They're coming from the same gene pool, exposed to the same environment, more or less. There must be something to do with the relationship between the two [identical twins]."
Zaretsky examined the World War II Veterans Twins Registry, which contains data on 11,832 identical and 15,062 fraternal twins born between 1917 and 1927. Researchers sent questionnaires to the twins in the late 1960s and mid-1980s and received 14,300 and 9,475 responses, respectively.
While the surveys asked a variety of questions about topics such as smoking, alcohol consumption, exercise level, and participation in church and community, only one factor -- closeness with one's twin -- boosted life span among identical twins.
The identical twins who talked to each other at least once a month were more likely to live longer than those who didn't, Zaretsky discovered. "It wasn't the same for fraternal twins. It didn't seem to matter whether they communicated frequently or not," he says.
Zaretsky reports his findings in the June issue of the Journals of Gerontology Series A: Biological and Medical Science.
On the whole, identical twins lived 82 years on average vs. 80.5 years for fraternal twins. Inherited tendencies to live longer seemed to affect life span in only about 20 percent to 30 percent of the twins.
Other factors may be at play, Zaretsky adds. Identical twins are also more likely to exercise and avoid smoking.
The closeness between identical twins may have something to do with a special bond between them, Zaretsky says. "From the stories I hear anecdotally, many identical twin pairs are constantly communicating with each other. These aren't young people but older people, who have responsible positions which are demanding of their time, but they're on the phone to each other several times a day."
Meri Wallace, a New York City child and family therapist, has watched identical twins at the infant stage. "They just spend time with each other and not the other children, and often have a secret language," she says. "When they look at each other, they see themselves. It's an incredible bond."
Fraternal twins may be more "loosely bound," especially since they share less of a genetic bond to each other, says Wallace, author of a book called Birth Order Blues.
Zaretsky said it's possible that close relationships may actually affect the brain. His next step is to study the brains of twins by using a form of magnetic resonance imaging (MRI) technology.
To learn more about twins, visit the National Organization of Mothers of Twins Clubs, Inc.. Or try The Center for the Study of Multiple Births.