1. A life history perspective on size, health and adult mortality in the Gambia Rebecca Sear London School of Economics

2. Life history theory and demography Life history is concerned with allocation of energy over the life course How do organisms solve problem of adaptively allocating energy between growth, body subsistence and repair, and reproduction? Demography a key component of LHT – both a constraint on, and an outcome of, life history decisions

3. Adult mortality and resource availability This study investigates relationship between adult mortality and resource availability Measures of resources availability –Height –BMI –Haemoglobin (Hb)

4. Height Height: measure of past investment in growth –Previous research: Human studies (height): –height usually found to be negatively correlated with mortality –but recent evidence suggests mortality higher in tall people for certain causes Animal studies (size): –caloric restriction increases longevity –costs of fast growth

5. BMI & Hb BMI & Hb: measures of current body condition –Mortality should be inversely related to both BMI and Hb but What is the shape of the relationship? Does this relationship differ between women and men? –Previous (human) studies suggest a non-linear relationship between BMI and mortality

6. Analysis Analysis of adult (21+ years) mortality by: –Height –BMI –Haemoglobin level Investigating both whether there is a relationship, and the shape of the relationship For both women and men

7. Data Data collected 1950-74 4 rural villages Demographic data collected continuously Anthropometric surveys conducted (at least) annually

8. Adult anthropometrics WomenMen Height (cm) Mean158168 Range122-178128-197 N (measurements)13,2909,680 BMI Mean20.720.4 Range12-4013-30 % underweight1613 % overweight41 N (measurements)11,5989,674 Hb (g/dl) Mean11.813.5 Range2-173-20 % anaemic4833 N (measurements)10,9869,653

9. Height and age

10. BMI and age

11. Hb and age

12. Adult mortality

13. Methods Discrete-time event-history analysis on probability of adult death (21+ years) Separate models for women and men Anthropometric variables entered as time dependent Controlled for birth cohort

14. Results WomenMen VariableEstimate (SE) Constant 84.3 (37.0)*4.81 (4.64) Age-0.02 (0.03) 0.07 (0.01)* Height Height 2 -0.95 (0.47)* 0.003 (0.001)* 0.005 (0.01) BMI BMI 2 -0.86 (0.27)* 0.02 (0.01)* -0.91 (0.39)* 0.02 (0.01)* Hb Hb*age -0.68 (0.14)* 0.01 (0.002)* -0.23 (0.03)* No. deaths182172 No. survivors823683

15. Height and mortality

16. BMI and mortality

17. Hb and mortality

18. Conclusions I Height: –matters for female mortality – though relationship not linear –Why not for men? Measures of current body condition significantly correlated with mortality for both sexes –High BMI increases mortality (costs of fat storage?), but low BMI more important –Hb important for both sexes, especially women (maternal mortality?)

19. Conclusions II Clearly, there is variation in adult mortality by resource availability Though these relationships tend not to be linear Current health/body condition matters for both sexes, height only for women –growing tall has costs for women (or linked to greater reproductive effort of tall women?), but apparently not for men? Influence of genetic factors?