Longitudinal evidence that fatherhood decreases testosterone in human males

Longitudinal evidence that fatherhood decreases testosterone in human males
Lee T Gettler et al.; 2011
http://www.pnas.org/content/108/39/16194.full


Abstract

In species in which males care for young, testosterone (T) is often high during mating periods but then declines to allow for caregiving of resulting offspring. This model may apply to human males, but past human studies of T and fatherhood have been cross-sectional, making it unclear whether fatherhood suppresses T or if men with lower T are more likely to become fathers. Here, we use a large representative study in the Philippines (n = 624) to show that among single nonfathers at baseline (2005) (21.5 ± 0.3 y), men with high waking T were more likely to become partnered fathers by the time of follow-up 4.5 y later (P< 0.05). Men who became partnered fathers then experienced large declines in waking (median: −26%) and evening (median: −34%) T, which were significantly greater than declines in single nonfathers (P < 0.001). [why did they use single nonfathers as control?] Consistent with the hypothesis that child interaction suppresses T, fathers reporting 3 h or more of daily childcare had lower T at follow-up compared with fathers not involved in care (P < 0.05). Using longitudinal data, these findings show that T and reproductive strategy have bidirectional relationships in human males, with high T predicting subsequent mating success but then declining rapidly after men become fathers. Our findings suggest that T mediates tradeoffs between mating and parenting in humans, as seen in other species in which fathers care for young. They also highlight one likely explanation for previously observed health disparities between partnered fathers and single men.

Reduced Midlife Physical Functioning Among Never Married and Childless Men

Reduced Midlife Physical Functioning Among Never Married and Childless Men: Evidence from the 1946 British Birth Cohort Study

Jack M Guralnik et al., 2011

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3030619/

Abstract

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Background and Aims

Marital and parental role characteristics are important factors in both men and women’s health. Most studies to date have either focused on disease specific outcomes or summary measures of self-reported health rather than using functional tests of performance. The goal of this study is to investigate the extent to which marital and parental role characteristics are associated with midlife physical function.

Methods

Design

Prospective birth cohort study.

Setting

England, Scotland, and Wales.

Participants

1353 men and 1411 women followed up since their birth in 1946.

Main outcome measure

Handgrip strength, timed chair rising, and standing balance tests at age 53 years were used to calculate an aggregate physical performance score that ranged from 0 (poorest score) to 2.81.

Results

The mean physical performance score was 1.42 (SD 0.42) for men and 1.30 (SD 0.37) for women. By age 53 years, 11% of men and 8% of women had married but remained childless; 6% of men and 4% of women had never married. Never married ( 1.15; 95% CI: 1.06, 1.24) and childless married men ( 1.36; 95% CI: 1.30, 1.42) had significantly poorer physical performance score than married men with children ( 1.46; 95% CI: 1.43, 1.48). These relationships remained after adjustment for adult social class and employment status, own educational attainment and body mass index at 53 years (beta=−0.18, 95% CI: −0.27, −0.09 for never married and beta=−0.09, 95% CI: −0.16, −0.03 for childless married, compared with married men with children). Of those men who had never married 28% reported they were not working due to long-term health problems compared to 5% in both childless married men and married men with children. There were no marked differences in functional outcomes among women.

Conclusions

In this representative middle-aged population, unmarried and childless men faced greater risk of poor midlife physical function, even after adjustment for confounders. These findings suggest that for men, marriage and parenthood protect against functional decline in midlife. Alternatively, physical performance may be a marker of poorer health in earlier life, which affects the chance of marriage and parenthood.

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