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The singular world of twins and twin studies

Are Younger Looking Twins Healthier?

Do healthier twins look younger than their less healthy co-twins?

Does how you like reflect your general physical health? Twins studies can provide answers. Dr. Kaare Christensen and his colleagues in the United States, New Jersey, England, Germany and The Netherlands have produced an important and creative twin study on perceived aging as a marker of biological aging (Christensen, Thinggaard, McGue,  Rexbye, Hjelmborg, Aviv, et al., 2009). Ratings of perceived age were made of photographs of 387 same-sex twin pairs who had participated in the Longitudinal Study of Aging Danish Twins (LSADT). Raters included 20 female geriatric nurses, 10 male student teachers and 11 older women. Twins’ years of survival were obtained through the Danish Civil registration system. Measures of physical functioning included self-reported physical strength (e.g., walking up two flights of stairs) and grip strength (values on a Smedley Dynamometer). Cognitive functioning measures included the mini-mental state examination and five short cognitive tests. Leucocyte telomere length was assessed, given that shorter length is associated with diseases related to aging and to mortality.

Results showed that perceived age was significantly associated with survival, even after controlling for chronological age, sex and the rearing environment. Furthermore, the relationship between perceived age and survival was maintained even after controlling for physical and cognitive functioning. It was especially interesting that the greater the co-twin difference in perceived age, the greater the likelihood that the older looking twin died first. Perceived age, when controlled for chronological age and sex, also correlated significantly with physical and cognitive functioning, and with leucocyte telomere length. Thus, perceived age appears to be a valid index of patient health.

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This paper was accompanied by a pair of composite photographs. One picture displays the average appearance of ten sets of younger looking seventy-year-old twins, while the other picture displays the older looking co-twins. The difference between the two final images is striking.

This article was excerpted from an article currently in press in the journal TWIN RESEARCH AND HUMAN GENETICS.

 

Nancy L. Segal, Ph.D., is a Professor of Psychology and Director of the Twin Studies Center, at California State University, Fullerton.

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