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Defining chronic diseases

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Title: Defining chronic diseases


1
Defining chronic diseases
  • Chronic diseases are difficult to define by using
    the well-known criteria of
  • causation,
  • acuteness,
  • age of onset,
  • activity restriction,
  • period of illness and
  • premature mortality.

2
Defining chronic diseases
  • They are mostly characterized by
  • complex causality,
  • multiple risk factors,
  • a long latency period,
  • a prolonged course of illness, and
  • functional impairment or disability.

3
Arrival of the chronic disease epidemic
  • Chronic diseases are not new to human societies.
    Prehistorical and historical evidence clearly
    shows that our ancestors suffered from a variety
    of chronic diseases including osteoarthritis and
    diabetes (Hinkle 1987).
  • However, it was not until the twentieth century
    that chronic diseases began to dominate the
    health scene their prevalence is now greater
    than at any earlier period in human history

4
Arrival of the chronic disease epidemic
  • Up until the nineteenth century, infectious
    diseases and injury dominated the health of all
    populations even though descriptions of chronic
    diseases and conditions such as coronary heart
    disease, atherosclerosis and diabetes among
    affluent sections of the society were beginning
    to accumulate (Cohen 1989).
  • The growing impact of chronic diseases and
    conditions such as stroke, cancer, renal disease
    and high blood pressure was not fully appreciated
    until the early part of the twentieth century.

5
Geography of Chronic Disease
  • What are the determinants/risk factors of chronic
    diseases such as heart disease, cancer, asthma?
  • Why a geography of chronic disease?

6
Why a Geography of Chronic Disease?
  • Examining chronic disease at the lowest available
    level of data aggregation (local level) is
    beneficial in highlighting localized rate
    variations.
  • Geographic patterns that remain after variations
    due to known factors have been extracted can be
    used to suggest new factors responsible for the
    remaining variations in measures of chronic
    disease e.g., cancer
  • Such information enable public health officials
    to target additional resources to specific
    locations.

7
Coronary Heart Disease (CHD)
  • One in five men and women have some form of CVD.
  • Although the odds for men to develop a CVD before
    the age of 60 exceed that of women (one in three
    for men and 1 in 10 for women), women develop CVD
    at a higher rate in the postmenopausal years.

8
Coronary Heart Disease (CHD)
  • Coronary heart disease (CHD) mortality is
    associated with social and material deprivation,
    though the principle feature of sudden and
    unexpected coronary heart disease mortality, is
    uncertain.
  • In general, instances of mortality from CHD is
    not uniformly distributed throughout regions, as
    distinct geographical hot spots exist where
    mortality is usually greater than expected.

9
Examples of Geographical studies of CVD
  • Soo et al. (2001 Nottinghamshire, England)
  • Barker and Martyn, (1991 England Wales)

10
Geography of Coronary Heart Disease
Nottinghamshire, England
  • Soo et al. 2001 conducted a population based,
    retrospective study in the County of
    Nottinghamshire, England
  • County has 191 electoral areas. In the 4 years
    from 1 January, 1991 to 31 December, 1994
  • 1634 patients sustained a cardiac arrest
    attributed to a cardiac cause
  • The overall crude mean incidence rate of
    community cardiac arrest per electoral area was
    40.2 per 100 000 population (range 0121.2).

11
Geography of Coronary Heart Disease
Nottinghamshire, England
  • Thirteen electoral areas, relatively deprived
    according to the Townsend score, had a
    significantly greater than expected incidence
    rate of cardiac arrest (median of 75.6100 000
    per electoral area interquartile range (IQR)
    65.3, 83.8).
  • Twelve relatively affluent electoral areas had a
    significantly lower than expected incidence rate
    (median of 18.5100 000 per area (IQR 13.0,
    28.7).
  • See map below.

12
Geography of Coronary Heart Disease
Nottinghamshire, England
13
Geography of Coronary Heart Disease
Nottinghamshire, England
  • After adjusting for deprivation index, there were
    no differences in coronary heart disease (CHD)
    mortality and community cardiac arrest in urban
    and rural electoral areas.
  • Apart from response times by ambulance crews, the
    events that follow the cardiac arrest such as
    bystander resuscitation, ventricular fibrillation
    found as the presenting rhythm and survival were
    similar in all electoral areas.

14
Geography of Coronary Heart Disease
Nottinghamshire, England
  • Conclusions
  • Increasing level of deprivation is associated
    with areas of increased incidence of
    out-of-hospital cardiac arrest in
    Nottinghamshire, and the effect is apparently
    different from that on CHD mortality.
  • Strategies should aim at improving survival in
    areas identified as having high rates of
    community cardiac arrest.

15
Geographical studies of CVD
  • Barker and Martyn, (1991 England Wales)
  • A possible explanation for the geographical
    differences in mortality from cardiovascular
    disease in England and Wales is that its causes
    begin to operate not in adult life but during
    fetal development and infancy.
  • Infant mortality
  • Animal studies
  • Studies in Humans

16
Infant mortality and CVD
  • Infant mortality is, of course, no more than a
    general indicator of adverse environmental
    conditions
  • Records of infant mortality dating from the
    beginning of the century allow current death
    rates in the 212 local authority areas of England
    and Wales to be compared with infant mortality
    rates in the same places 60 or more years ago.

17
Infant mortality and CVD
  • The correlation between past infant mortality and
    current mortality from cardiovascular disease (r
    0.73) is strikingly close.
  • This relationship implies that some aspect of
    poor living conditions in early childhood
    determines risk of cardiovascular disease in
    adult life.

18
Infant mortality and CVD
  • The records of infant mortality in England and
    Wales are sufficiently detailed to allow neonatal
    mortality (i.e., deaths before one month of age)
    to be distinguished from post-neonatal mortality
    (i.e., deaths between the ages of one month and
    one year).
  • A further analysis using these separate
    categories showed that adult cardiovascular
    mortality is more closely linked to neonatal
    mortality 60 years earlier than to post-neonatal
    mortality
  • Neonatal mortality in the past was high in places
    where many babies were born with low birth
    weight.

19
Infant mortality and CVD
  • Neonatal mortality is also known to have been
    associated with high maternal mortality.
  • High rates for both neonatal and maternal
    mortality were found in places where the physique
    and health of women were poor.
  • Cardiovascular disease is therefore associated
    more strongly with poor maternal physique and
    health and poor fetal growth than with
    conditions, such as overcrowding, that predispose
    to high post-neonatal death rates.

20
Animal studies and CVD
  • Ideas about the importance of early life in
    determining risk of disease in adulthood are
    reinforced by studies in animals
  • Transient events in prenatal or early postnatal
    life have permanent and profound effects on
    physiology though such effects may remain latent
    until the animal is mature.

21
Animal studies and CVD
  • A female rat injected with a few micrograms of
    testosterone propionate during the first four
    days of life develops normally until puberty.
  • Only then does it become apparent that the
    hypothalamic neuronal substrate that mediates the
    cyclic release of gonadotrophins has been
    irreversibly altered to a male pattern when,
    despite adequate ovarian and pituitary function,
    the animal fails to ovulate or show normal
    patterns of female sexual behaviour.
  • The same injection of androgen given when the
    animal is 10 days old has no effect on
    reproductive function.

22
Animal studies and CVD
  • In another example, the nutrition of pregnant and
    lactating rats was manipulated.
  • The adult body size of these rats was more
    powerfully determined by their mothers' nutrition
    during pregnancy and lactation than by their
    genetic constitutions.
  • Under-nutrition during pregnancy stunted the
    growth of the offspring and this effect could not
    be reversed by an optimal diet after birth.

23
Animal studies and CVD
  • Nutritional deprivation in early life affects the
    size and DNA content of different organ systems,
    depending on the precise time at which it occurs.
  • In rats, a brief period of energy restriction
    immediately after birth caused a profound
    reduction in the weight of the liver, spleen, and
    thymus, while brain and skeletal muscle were
    spared.
  • Energy restriction immediately after weaning
    reduced only the weight of the thymus.

24
Studies in Humans and CVD
  • The question explored is whether the programming
    effect of the early environment applicable to the
    pathogenesis of cardiovascular disease in humans
  • This was done by studying adults in middle and
    old age whose growth and development in infancy
    was recorded in Hertfordshire, UK.
  • From 1911 onwards, every baby born in the county
    of Hertfordshire was weighed at birth, visited
    periodically by a health visitor throughout the
    first year, and weighed again at one year of age.

25
Studies in Humans and CVD
  • The records of these visits have survived so that
    it is possible to trace men and women born about
    60 years ago and to relate these measurements to
    the later occurrence of illness and death and to
    the level of known risk factors for
    cardiovascular disease.
  • In the first study, 6500 men born in eight
    districts of the county between 1911 and 1930
    were followed up.

26
Studies in Humans and CVD
  • Table I shows their standardized mortality ratios
    for ischemic heart disease according to weight at
    one year the ratios fall steeply as weight at
    one year increases. There are similar trends with
    increasing birth weight, though the relation is
    not as strong as with weight at one year.
  • These findings prompt questions about mechanism.
  • There is now evidence that haemostatic variables,
    glucose tolerance, blood pressure, and lipid
    metabolism are all susceptible to the programming
    effects of the environment in early life.

27
Studies in Humans and CVD
Standardized mortality ratios for IHD according
to weight at one year in 6500 men during
1911-1930 in Hertfordshire, England.
Source Barker Martyn 1991
28
Studies in Humans and CVD
  • High plasma concentration of fibrinogen is a
    strong predictor of increased risk of both
    ischemic heart disease and stroke.
  • Fibrinogen concentrations have been measured in
    591 men aged 59 to 70 years still living in
    Hertfordshire.

29
Studies in Humans and CVD
  • Table II shows that concentrations are inversely
    related to weight at one year of age.

Source Barker Martyn 1991
30
Studies in Humans and CVD
  • The inverse relation between systolic blood
    pressure and birth weight present in the
    Hertfordshire men is shown in table IV.
  • Table IV Mean systolic blood pressure in men
    aged 59 to 70 years

Source Barker Martyn 1991
31
Studies in Humans and CVD
  • A similar relation has also been found in a
    national sample of men and women at the age of 36
    years.
  • In contrast to plasma concentrations of
    fibrinogen and rates of glucose intolerance,
    blood pressure in these men is not related to
    weight at one year independently of birth weight,
    nor is it related to adult height.
  • This may indicate that the critical period when
    blood pressure is sensitive to programming is
    during fetal life rather than infancy.

32
Studies in Humans and CVD
  • These discoveries have implications both for the
    pathogenesis of cardiovascular and other
    diseases, and also for maternal and infant health
    at specific locations.
  • The relations between early growth and risk
    factors and rates of disease are continuous.

Source Barker Martyn 1991
33
Studies in Humans and CVD
  • Plasma levels of fibrinogen (table II), the
    prevalence of impaired glucose tolerance (table
    III), and levels of systolic blood pressure
    (table IV) fall progressively up to the highest
    values of weight at one year or birthweight.
  • If the criterion for successful fetal and infant
    growth is adult health and longevity, we may no
    longer be entitled to assume that a baby of
    average birthweight and weight in infancy has
    necessarily achieved its optimum weight.

Source Barker Martyn 1991
34
Geography of CVD
  • The results of these studies show that retarded
    growth in fetal life and infancy is strongly
    related both to mortality from cardiovascular
    disease and to adult levels of some of its known
    risk factors.
  • Any argument concerns the extent to which this
    relation should be interpreted as being causal.
  • In broad terms there are three possible
    explanations for our findings.
  • The first is that birthweight is merely a marker
    for adverse environmental influences that act in
    later life.

Source Barker Martyn 1991
35
Geography of CVD
  • Although this interpretation can just be
    sustained if one is prepared to view the
    ecological data in isolation, it cannot account
    for the results of follow up studies of
    individuals.
  • In Hertfordshire birth weight was not associated
    with social class, either at birth or currently.

Source Barker Martyn 1991
36
The Geographic Variation of Cancer Incidence in
Ontario
  • Walter et al. 1994
  • Examination of the spatial pattern of cancer
    incidence in Ontario
  • Cancer incidence were calculated for 22 cancer
    sites in 49 counties in Ontario during 1976-1986.

37
The Geographic Variation of Cancer Incidence in
Ontario
  • The analysis reveal a number of cancers with
    significant patterning of risk
  • Further work is needed to relate the cancer data
    to other information on potential life-style and
    environmental factors

38
Geography of Cancer
  • Stomach cancer
  • Strong spatial aggregation was apparent in both
    sexes.
  • Northern Ontario and some areas near Lake Ontario
    had high rates, while central Ontario had lower
    rates
  • Correlations between sexes and over time were
    high

39
Geography of Cancer
  • Lung cancer.
  • There were strong geographic patterns for both
    sexes, with high correlations between sexes and
    over time.
  • High rates were found in large areas of the
    northeast and east and in some counties near Lake
    Ontario and in the southwest


40
Geography of Cancer

  • Malignant melanoma of the skin
  • Female rates showed a significant clustering
  • Elevated risk in a group of counties north of
    Toronto



41
Geography of Cancer

  • Cervical Cancer
  • Weak and dispersed geographic pattern with strong
    persistence over time
  • High rates tended to occur in northern Ontario
    and around Georgian Bay
  • Rates in the southwest were generally low



42
Geography of Cancer

  • Corpus uteri cancer
  • Significant spatial pattern with persistence over
    time
  • Rates were low in northern Ontario and generally
    high in the southwest



43
Geography of Cancer

  • Prostatic cancer
  • Strong spatial aggregation
  • A risk gradient by latitude, with low rates in
    the north and high rates in the southwest
  • Low correlation over time, suggesting a transient
    or recent effect



44
Geography of Cancer




45
Geography of Cancer

  • Several cancers show regional variations, but the
    explanation for the variability requires an
    understanding of the possible impact of
    environmental factors
  • However, migration and latency are major
    problems.


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