Independent changes in female body shape with parity and age: A life-history approach to female adiposity.

Both aging and reproduction have been shown to influence female body shape in industrialized populations, involving redistribution of fat from lower to upper body regions. However, the extent to which effects of parity vary by age and the extent to which age affects shape independent of parity remain unclear. We studied shape variability in relation to age and parity in a cross-sectional survey of 4,130 white British women, using three-dimensional photonic scanning. In women < or =40 years, bearing children was associated with increased abdominal and reduced thigh girths, independent of age and BMI. Very few such differences were statistically significant in women >40 years, suggesting the effects of parity on shape wash out over time. In nulliparous women, aging was associated with shape variability, independent of BMI, with a similar pattern of associations evident in women both < or =40 and >40 years. Our data support previous findings of "covert maternal depletion" in relation to parity, but show that this is merely a more pronounced component of a general strategic shift of fat from lower to upper body with age. These findings are consistent with a life-history model of female energy stores being allocated to competing "reproduction" and "maintenance" depots, with the optimal trade-off strategy changing with age and with that strategic shift accelerated by bearing children. This model is relevant to the "grandmother hypothesis." The dual effects of age and parity on fat distribution substantially resolve by old age the profound sexual dimorphism in adiposity present at the start of adult life.