Lecture 19 : Heart Disease (2) Perinatal And Early Life Hypotheses Overview

1. Lecture 19 : Heart Disease (2) Perinatal And Early Life HypothesesOverview • FORSDAHL’S HYPOTHESIS • OTHER ECOLOGICAL STUDIES • INDIVIDUAL LEVEL STUDIES • DISCUSSION

2. Forsdahl’s Hypothesis • Forsdahl found major variations in heart disease rates between Norwegian counties, but they did not relate to contemporary living conditions. • They were, however, rated to patterns of infant mortality half a century previously. • Infant mortality rates were now similar in most areas. • As infant mortality tends to be closely related to living conditions, he concluded that heart disease rates were highest in areas which had fastest rates of improvements in living conditions. • He hypothesised that people brought up in poverty had a reduced tolerance to certain types of fat.

3. Criticisms Of Forsdahl Elford et al. (1992) criticise Forsdahl: • Forsdahl provides no direct evidence that prosperity following poverty is a factor – the initial poverty may be sufficient in itself. • Forsdahl did not consider factors in adult life (e.g. smoking). These may have the same geography as past infant mortality.

4. Three Possibilities Taking these criticisms inot account, we are left with three possibilities: • Adult heart disease is a function of initial poverty followed by later prosperity (as hypothesised by Forsdahl); • Adult heart disease is a function of childhood poverty, irrespective of whether it is followed by prosperity or not; and • Adult heart disease is a function of risk factors (such as smoking) in adult life - the orthodox view.

5. Other Ecological Studies (1) • Buck and Simpson (1982) found infant mortality in US in 1917 was correlated with adult mortality in 1961 and 1971, but that infant mortality in 1927 was not. This provides partial support for hypotheses A and B. • Williams et al. (1979) found heart disease in England and wales was correlated with past infant mortality, but that the pattern of infant mortlaity had not changed. This provides support for B, but not for A. • Barker and Osmond (1986) found high correlations between past infant mortality and a variety of adult causes of death at present. This suggests that mortality may be related to deprivation and is consistent with hypotheses B and C.

6. Other Ecological Studies (2) • Barker and Osmond (1987) found that adult mortality in three similar and neighbouring towns (Burnley, Colne and Nelson) varied and was similar to infant mortality patterns in the early 1900s. This in turn was associated with living conditions and life histories of the mothers at the time. This lends support to hypothesis B. • Osmond et al. (1987) examined 2 million death certificates. Although about half of the sample had moved since birth, they found that their place of birth was a better predictor of heart disease than current location. This lends more support to hypothesis B than C.

7. Other Ecological Studies (3) • Barker and Osmond (1986) found adult Bronchitis mortality was strongly correlated with previous postneonatal mortality, stroke with neonatal mortality and heart disease with both. Neonatal mortality tends to be associated with foetal development / maternal health, whereas postneonatal mortality is associated with living conditions after birth (e.g. overcrowding). This suggests conditions around time of birth have a long-lasting impact (i.e. hypothesis B).

8. Individual Level Studies (1) • Barker et al. (1989) tracked down 6,500 men on whom there were existing records taken by health visitors when they were infants. There was a strong relationship between weight at 12 months and heart disease mortality (but not other causes). There was also an association with other risk factors (e.g. systolic blood pressure). This suggests that factors which promote prenatal and postnatal growth may reduce deaths from heart disease.

10. Individual Level Studies (2) • In a second study of 449 men and women in Preston, Barker at al. (1990) found that present day blood pressure was correlated with placental weight. A large placenta often indicates poor foetal nutrition. This suggests that the risks of adult heart disease may be ‘programmed’ before birth.

11. Discussion • Forsdahl suggested that childhood factors may be a more important determinant of adult heart disease rates than present day living conditions / lifestyles. • Barker and his associates suggested the critical time was immediately after birth, but later work has tended to suggest conditions in the womb may be more critical. • Dutch studies of survivors of the Dutch famine winter at the end of World War II suggests the critical period may be within the first few weeks after conception.