Weight gain is associated with shorter lifespan: a longitudinal study of New Zealand soldiers serving in both world wars.

Obesity is an increasing public health concern with important mortality consequences. Weight gain or maximum adult BMI, not BMI at one point in time, has been shown to be an important risk factor in cohorts studied recently during an era of rapid increase in population levels of overweight and obesity. However, there is limited evidence on individual weight trajectories from cohorts born before the mid-twentieth century. Archival world war military personnel files from New Zealand are freely available online, and identify service in both wars. A pilot study of 316 soldiers confirmed the files contain sufficient information to examine health trajectories and lifespan. Because this cohort are now entirely deceased, nearly the entire sample can be found in death records to estimate the impact of weight increases on lifespan. Weight change over 20-30 years and its relationship with lifespan is examined using ordinary least squares regression. The study demonstrates that military records are a feasible source for collecting data on adult weight and health trajectories in the first half of the twentieth century. Although this sample is likely to be composed of men fitter than average, there is a clear pattern of increasing weight from early to mid-adulthood. Weight gain from early adulthood to middle-age was found to be more strongly associated with mortality than weight in early adulthood. A one unit increase in BMI over the inter-war period was found to be associated with an 8 month decline in lifespan. These results confirm that weight gain in adulthood has an important impact on mortality in an earlier birth cohort than previously studied, and that data exist to measure any changes more precisely over time.