A life history perspective on size health and adult mortality in the gambia
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A life history perspective on size, health and adult mortality in the Gambia. Rebecca Sear London School of Economics. Life history theory and demography. Life history is concerned with allocation of energy over the life course

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A life history perspective on size, health and adult mortality in the Gambia

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A life history perspective on size, health and adult mortality in the Gambia

Rebecca Sear

London School of Economics


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


Adult mortality and resource availability

  • This study investigates relationship between adult mortality and resource availability

  • Measures of resources availability

    • Height

    • BMI

    • Haemoglobin (Hb)


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


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


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


Data

  • Data collected 1950-74

  • 4 rural villages

  • Demographic data collected continuously

  • Anthropometric surveys conducted (at least) annually


Adult anthropometrics


Height and age


BMI and age


Hb and age


Adult mortality


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


Results


Height and mortality


BMI and mortality


Hb and mortality


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?)


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?


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