Number of children and body composition in later life among men and women: Results from a British birth cohort study

Abstract

Background Although research has found associations between increasing number of children and higher body mass index (BMI), there has been limited research investigating the association with body composition despite abdominal fat being associated with cardiovascular and metabolic risk independently of general adiposity. Most existing research has focussed on women, but investigating the relationship in men can help distinguish biological effects of pregnancy from social pathways related to parenthood. Methods Using the MRC National Survey of Health and Development (NSHD) multiple regression models were applied to test associations between number of children and body composition at age 60-64 (N=2229) and body mass index (BMI) and waist circumference (WC) at ages 60-64 and 69 (N=2149). Results In adjusted models, associations were observed between increasing numbers of children and increasing fat-adjusted lean mass index in women (p=0.06). Among men, those with children had 0.59kg (95% CI: 0.15 to 1.02) greater lean mass index than those without and fat:lean mass ratio was greater in those with 4+ children because of their slightly higher mean fat mass. Weak evidence of a higher android:gynoid mass ratio in women with children (0.03, 95% CI: 0.00,0.06, p=0.1) was observed with no associations with fat mass index or android or gynoid fat mass. Increasing BMI was observed with increasing parity in women at 60-64 and more strongly at 69 years where associations among men were also observed more clearly. Conclusion There was little evidence of a consistent association between number of children and body composition in early old age. The strongest associations are observed for lean, rather than fat mass, and in men rather than women, suggesting little evidence of biological effects of pregnancy in women. The results indicate social pathways associated with parenthood are the likely underlying mechanisms, with suggestion there may be selection into parenthood among men.