Life course epidemiology

Life course epidemiology

OVERVIEWIntroduction

Introduction to life course epidemiology.

DefinitionHistoryTheories and implications on policy

Research example: Early life origins of obesity in the Philippines.

LEARNING OBJECTIVESIntroduction

1. Define life course epidemiology

2. Describe key theories in life course

epidemiology.

3. Discuss policy implications of different life

course theories.


The study of how physical and social experiences across the life course impact life long health and well

being.



being.

Social exposures

Essentially, anything outside of ourselves.

Exposures that are shared with others.



being.



being.

Life course theories

Critical periodsSensitive periods

AccumulationChains of risk

Thrifty Phenotype Hypothesis

Gluckman and Hanson. Developmental Origins of Disease Paradigm: A Mechanistic and Evolutionary Perspective. Pediatric Research (2004)

Obesity is a global problem

Obesity is a global problem

Obesity is viewed as a purely individual level problem.

We know environment matters…

• The suddenness of the obesity pandemic precludes changing biology as an explanation.

But why is there so much variation in body size, even among people sharing an environment?

Small size at birth and later central adiposity

Famine studies• Dutch hunger winter (1944-1945)

Military conscripts whose mother experienced the famine during the second half of pregnancy were less likely to be obese.

Military conscripts whose mother experienced the famine during the first half of pregnancy were more likely to be obese.

Where is the interaction with environment?

So how can we more rigorously test the mismatch hypothesis in humans?

• Look for interactions between fetal exposures and post-natal environments.

• Move away from birth weight as a proxy measure of the fetal environment.

The Cebu Longitudinal Health and Nutrition Survey

• Prospective, longitudinal birth cohort study design.

http://www.cpc.unc.edu/projects/cebu


• A single stage cluster sampling procedure was used to randomly select 33 administratively defined communities called barangays.


• Pregnant women residing in these barangays were recruited for the study in 1982 and 1983, and those who gave birth between May 1, 1983, and April 30, 1984, were included in the sample.


A baseline interview was conducted among 3,327 women during their 6th or 7th month of pregnancy.

• Another survey took place immediately after birth; there were 3,080 non-twin live births which make up the CLHNS birth cohort.


• Subsequent surveys were conducted bi-monthly to age 2, then in 1991, 1994, 1998, 2002, and 2005.


• Detailed data on the birth cohort, their mothers, and the barangays they live in.

How do we measure obesogenic environments?

Independent variables• 2005 Individual-level SES

– Assets

– Income

– Education

– Marital status

• 2005 Barangay level urbanicity

Dependent variables• Obesity

• BMI• WC

Defining Obesity A condition of abnormal or excessive

fat accumulation in adipose tissue, to the extent that health may be impaired.

- World Health Organization







BMI Height over weight squared

Conceptually, weight independent of height

Simple to measure

Highly correlated with % body fat

Interactions• We must “investigate more carefully the extent

of interactions between characteristics of individuals and the features of places associated with varying health risks” (Cummins, Curtis, Diez-Roux, & Macintyre, 2007).

• SES interacted with Urbanicity

Can fetal influences modify the impact of obesogenic environments?

Less about birth weight

Estimating interactions between prenatal characteristics and the

postnatal environment

Maternal constraint• Hypothesized causes…

– Maternal height

– Hip circumference

– BMI

– Arm fat area

– Parity

– Caloric intake

– Protein intake

Science

Life course epidemiology