Body weight is not always a good predictor of longevity in mice

There have been some observations that low body weight and a low level of some hormones (e.g. IGF-1) during the first half of life are predictors of longer life in mice. However, contradictions in the available data on the biomarkers of aging and predictors of longevity have shown that the research in these fields has become a controversial pursuit. In our study we addressed the following questions: (i) Can particular physiological parameters (body weight, food intake, estrus function, body temperature, incidence of chromosome aberrations in bone marrow cells) measured at the age of 3 and 12 months be a predictor of longevity and the rate of tumor development in five strains of mice? (ii) Can a heavy body weight at the age of 3 and 12 months be a predictor of longevity and high tumor risk in five strains of mice? Mice of five strains-CBA, SHR, SAMR, SAMP and transgenic HER-2/neu (FVB/N)-were under observation from the age of 2-3 months until natural death. Body weight and temperature, food consumption, and estrous cycle were longitudinally studied in all animals. Tumors discovered at autopsy were studied morphologically. We calculated the life span's parameters (mean, maximum, mortality rate, mortality rate doubling time) as well as their correlation with other parameters studied. The longest living CBA mice have the lowest body weight at the ages of 3 and 12 months, the lowest food consumption, body temperature, incidence of chromosome aberrations and spontaneous tumor incidence. In comparison with all other mouse strains they also have the latest disturbances in estrus function and highest body weight gain. The shortest living transgenic HER-2/neu mice have the lowest weight at the ages of 12 months, the lowest body weight gain, maximal body temperature, the most rapid disturbances in estrus function and the highest incidence of chromosome aberrations and tumor incidence in comparison to all other mouse strains. Our findings have shown that heavier body weight at the age of 12 months is a predictor of longevity in female CBA and SAMP mice but not in SHR, SAMR and HER-2/neu mice. Excessive body weight at the ages of 3 or 12 months is not a predictor of increased tumor risk in the strains studied. In general, the existence and direction of a significant correlation between body weight and life span depends upon the animals' age and genotype.