Background: The rise in body mass index (BMI) during adulthood increases the risk for metabolic disorders, functional limitations and disability in old age. This twin study examined prospectively whether genetic and environmental influences on women's BMI also account for mobility 29 years later.
Methods: The sample consisted of 103 monozygotic and 114 dizygotic pairs of twin sisters reared together. Body mass index was initially evaluated in 1975, when the women were aged 42.6+/-3.4 years, and was followed-up in 1981, 1990, 2001 and 2004. Mobility was evaluated using the standardised 6-minute walking test in 2001, when the women were aged 68.6+/-3.2 years, and followed-up 3 years later. An investigation was made into how genetic and environmental influences on adult BMI accounted for mobility in old age using a genetic latent growth modelling approach.
Results: During the follow-up period, BMI increased by 17%. Midlife BMI was a significant predictor of mobility 29 years later. Genetic influences on BMI level and its rate-of-change accounted for 37% and 25% respectively, of the genetic influences on mobility later in life. The corresponding environmental influences on BMI level and its rate-of-change were 35% and 22%.
Conclusion: Genes predisposing to higher BMI across middle age increase the risk for poorer mobility in old age. Identifying those genes could lead to interventions targeted at preventing obesity and mobility loss later in life. However, modification of environmental factors, eg exercise and nutrition, remain the most feasible ways of influencing BMI and mobility across the life span.