Why? “The overwhelming view within psychiatry and psychology is that is due to genetic factors,” says Virginia Commonwealth University psychiatrist Kenneth S. Kendler. “Yet we know that extreme environmental adversities, such as abuse in childhood or wartime trauma, have a long-term impact on people.” Kendler had a hunch that environmental experiences also influence the set points for anxiety and depression.
His new study, which will be published in an upcoming issue of Psychological Science, a journal of the Association for Psychological Science, concludes that they do. Kendler and an international roster of collaborators — VCU colleagues Lindon J. Eaves, Erik K. Loken, Judy Silberg, and Charles O. Gardner; Nancy L. Pedersen and Paul Lichtenstein of Karolinska Institutet in Stockholm, Sweden; Christel M. Middeldorp and Dorret Boomsma of VU University, Amsterdam; and Chandra Reynolds of the University of California — find that life experiences play a central role in establishing the set points for anxiety and depression, perhaps even more than genes do.
Kendler used a group of research subjects time-honored for testing the effects of nature and nurture: identical twins, whose genes are the same, but whose life stories diverge, showing the effects of environmental factors on a developing person.
Scouring the world, he gathered a large and varied sample: nine data sets from longitudinal twin studies — a total of more than 12,000 twins, including 4,235 pairs and 3,678 unpaired twins, from three continents. The twins had all completed reports of their own symptoms of anxiety and depression, three times in eight of the studies; twice in the ninth. Each study covered five or six years. The youngest subjects were just under 11, the oldest almost 67.
Patching together a composite of these life segments — from pre-pubescence to early adulthood, middle age to retirement age — VCU’s Charles Gardner designed a series of statistical analyses, which yielded a clear curve. The set points of the 10-year-old pairs were the same or closely similar. As the twins moved through adolescence and adulthood, however, those points diverged increasingly, until the differences leveled out at around age 60.
The set points were stable — they did not wander all over the place — though not permanent; they were not necessarily the same for 50 years. But in examining the difference between those points in pairs of genetically identical people, the researchers saw that while genes may play a part in determining our emotional predilections, it is life that shows our moods the place they want to settle.
The study has implications beyond anxiety and depression, says Kendler. “Environmental experiences have a memory and stay with us. What governs the emotional set point of adults is a mixture of genetic factors and the total aggregate of environmental experiences.” The moral of the story? “If you want to be happy in old age, live a good life.”
Material adapted from Association for Psychological Science.