Reproduction, health and mortality in Gambian women Rebecca Sear London School of Economics Ruth Mace, University College London

Relationships between reproduction, health and mortality 1.Reproduction requires minimum body condition – predicts body condition will be positively correlated with successful reproduction 2.But reproduction costly – predicts reproduction should cause reduction in body condition and ultimately increase mortality rates –maternal depletion –costs of reproduction

Study site The Gambia

Data Collected from 4 rural villages since 1950 Demographic, anthropometric and genealogical data Until 1975 both fertility & mortality were high –TFR ~ 7, 5 q 0 ~ 0.43 After 1975 mortality dropped, but fertility remained high

Summary of anthropometry Non-pregnant adult women (n~11,600 measurements) : MeanMinMax Weight (kg) Height (cm) BMI Hb (g/dl) Age (yrs)

Evidence for costs of reproduction? Is reproductive effort correlated with mortality rate for women? Samples: –reproductive-aged women, years (~1000) –post-reproductive women, 50+ years (~400)

Measures of reproductive effort Giving birth Parity Timing of reproduction –age at first birth –age at last birth Intensity of reproductive effort –pace of reproduction –twins –boys

Mortality: reproductive-aged women Discrete-time event-history analysis Analysing effects of: –giving birth –parity –timing: age at first birth –intensity: sex of most recent birth twins Controlling for birth cohort

Results of mortality model: yrs VariableModel 1 ORp Age1.06<0.01 Birth year2.09<0.01 Parity0.83<0.01 Age first birth (ref 18-19) : <18 > NS Mother of twins0.66NS NS: intensity of reproductive effort: whether most recent birth was twin or male

Mortality: post-reproductive women Discrete-time EHA Analysing effects of: –parity –timing: age at first birth age at last birth –intensity: pace twins sons

Mortality and parity Median age at death (yrs)

Mortality and age at last birth Median age at death (yrs) 77 72

Results of mortality model: 50+ yrs VariableModel 1 ORp Age1.12<0.01 Parity0.97NS Nulliparous1.46NS Age first birth (ref 18-19) : <18 > NS Age last birth (ref 30-39) : <30 > NS <0.01 Mother of twins3.55<0.01 NS: sex composition

Conclusions Evidence for costs of reproduction inconclusive Mortality: –Giving birth clearly a risk factor –But other evidence suggests negative relationship between reproduction and mortality –EXCEPT twin mothers have higher post-reproductive mortality

Selection effects? Potential explanation for negative relationship between reproduction and mortality: –only healthy women can reach high parities, start reproducing early and stop reproducing late –less healthy women start later, stop earlier and have fewer births Solutions? –control for health in mortality analysis –use repeated measures anthropometric data

Controlling for health: yrs VariableModel 1Model 2 ORp p Age1.06< <0.01 Birth year2.09< <0.01 Parity0.83< <0.01 Age first birth (ref 18-19) : <18 > NS NS Mother of twins BMI before first birth 0.66NS NS

Controlling for health: 50+ yrs VariableModel 1Model 2 ORp p Age1.12< <0.01 Parity0.97NS0.94NS Nulliparous1.46NS1.20NS Age first birth (ref 18-19) : <18 > NS NS Age last birth (ref 30-39) : <30 > NS < NS <0.01 Mother of twins Height 3.55< <0.01 NS

Selection effects? Potential explanation for negative relationship between reproduction and mortality: –only healthy women can reach high parities, start reproducing early and stop reproducing late –less healthy women start later, stop earlier and have fewer births Solutions? –control for health in mortality analysis –use repeated measures anthropometric data

Conclusions Controlling for health does not affect relationship between reproduction and mortality: –inadequate measures of health? –protective effects of reproduction?