GLOBAL EPIDEMIOLOGY OF CHRONIC DISEASES

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Chapter 1

GLOBAL EPIDEMIOLOGY OF CHRONIC DISEASES

The Epidemiologic Transition

Chapter Objectives

    • Contrast global impact of chronic versus acute disease
    • Examine population differences in longevity
    • Define major theories of aging
    • Characterize the “epidemiologic transition”
    • Discuss “disease-specific” global death rates
    • Discuss selected major risk factors of disease
    • Discuss “Disability-Adjusted Life Years”
    • Present key features of chronic disease prevention

 

 

 

Major Topics

  • Global Pandemic of Chronic Diseases
  • World Population Growth
  • Increasing Global Longevity (Life Expectancy)
  • Gender Differences in Longevity
  • Aging and Chronic Disease
  • Free Radical Theory of Aging
  • Telomere Shortening and Aging
  • Declining Fertility in Women

 

 

 

Key Concepts

  • Epidemiologic Transition
  • Global Death Rates (Mortality)
  • Mortality in Developed Versus Developing Nations
  • Global Tobacco Pandemic
  • Global Obesity Pandemic
  • Malnutrition and Starvation
  • Disability Adjusted Life Years
  • Global Prevention of Chronic Diseases

Global Pandemic of Chronic Diseases

  • 2009 World Population = 6.8 Billion People
  • 61 Million Deaths
  • 38 Million Deaths (62%): Chronic Disease
  • 23 Million Deaths (38%): Acute Disease

World Population Growth

  • The number of living individuals on the planet continues to increase.
  • In 2009, there were 139 live births and 61 million deaths, a net gain of 78 million people.
  • The 2040 world population is projected to be nearly 9 Billion people.

Figure 1.1 World Population

Aging of the World Population

  • The world population is not only increasing in number but it is also growing older.
  • Two demographic parameters are driving these phenomena: longevity is increasing and the fertility rate is decreasing.
  • Worldwide, the average life expectancy (longevity) is 67 years.
  • Longevity is greater in women (70 years) than men (65 years).

Patterns of Longevity (Life Expectancy)

  • In the past half century, life expectancy has increased dramatically in the populations of developing nations such as China and India.
  • Live expectancy is lowest in less developed nations, particularly those in sub-Saharan Africa.
  • In highly developed nations (Japan, USA, Australia and European countries) longevity now approaches or surpasses 80 years and deaths are more likely due to chronic diseases of old age.
  • The Japanese people currently enjoy the greatest longevity, about 82 years.

Figure 1.2 Longevity Trends in Selected Nations

Figure 1.3 Global Longevity, 2011

Gender Difference in Longevity

  • Life expectancy (longevity) for women is 5-10 years greater than for men.
  • Reduced maternal mortality has widened the gender gap in longevity in developed nations.
  • The female survival advantage begins at conception (90% of male fetuses survive compared to nearly 100% of female fetuses).
  • Remarkably, about 90% of centenarians (individuals over 100 years of age) are female.

Figure 1.4 Life Expectancy, USA, Women and Men

Aging & Chronic Disease

  • The risk of death is elevated early in life, then remains low until age 40 years, after which it increases exponentially.
  • Likewise, the prevalence of many debilitating and life-threatening chronic diseases (arthritis, cancer, type 2 diabetes and COPD) rises exponentially with age after the 4th decade of life.
  • Nevertheless, disease is not the inevitable consequence of aging.
  • While certain pathologic conditions progress in parallel with the aging process, others, like asthma, remain constant or even decline late in life.

Figure 1.5 Characteristic Death Curve

Figure 1.6 Age-Specific Prevalence of Selected Chronic Diseases

Aging & Disease

  • Aging is driven by deterioration in cellular health.
  • Acceleration of aging in even one critical cell population may create a “weak link” for the entire system resulting in debilitation and death.

Theories of Aging

  • According to one theory, “aging is not a disease, but it increases vulnerability to disease” (Hayflick, 2007).
  • The “Free Radical Theory” of aging states that aging is a consequence of accumulating oxidative damage to cells and cellular components such as mitochondria over time (Harman, 1956, 1972).

Theories of Aging

  • The “Telomere Theory of Aging” states that as a critical fraction of cells reach their “Hayflick Limit” and are unable to replicate, then maintenance, defense and repair of the body become increasingly impaired (Hayflick, 1985, 2007).
  • The Hayflick Limit is reached when the loss of telomeres at the tips of chromosomes with each successive cell division becomes critical and further cell division is impeded.

Figure 1.7 Free Radical Theory of Cell Damage, Aging and Chronic Disease

National Fertility Rates

  • Over the past half century, the worldwide fertility rate (the average number of births per woman during the childbearing years) has been cut in half, from 5.0 in the 1950s to 2.5 in the 21st century.
  • In industrialized nations such as Canada, Germany, Great Britain and Japan, fertility rates are now well below the replacement rate.
  • In the USA, the fertility rate has decreased from 3.5 in the 1960s to 2.0 currently, only slightly below the replacement rate of 2.1.
  • Worldwide access to birth control has likely contributed to the general decline in the global fertility rate.

Figure 1.8 Selected Fertility Rates, 2009
(Number of Births/Woman in Reproductive Years)

Fertility in Women

  • A woman’s potential for childbearing begins to gradually decline between 20 and 30 years of age and then exponentially decreases until the end of the reproductive years at menopause
  • Widespread use of effective oral contraceptives, the accessibility of medical abortion and the shifting paradigm for women to pursue professional careers rather than start families have combined to delay their having children.
  • Certain family planning incentives and policies such as China’s “one child policy” in 1979 have also contributed to the steep decline in fertility in large populations of the world.

Figure 1.9 Pregnancy and Infertility Rates, Women, USA, 2009

Global Pattern of Death
Mortality in sub-Saharan Africa

  • The relatively young populations of sub-Saharan Africa have the highest annual death rates in the world (21 per 1,000).
  • Individuals in these nations have 3-4 times higher risk of dying than their peers in developed countries.
  • Hunger and malnutrition, parasitic diseases, infectious diseases and constant warfare ravage the health of young adults.
  • Chronic diseases (e.g., heart disease, stroke, diabetes and chronic obstructive pulmonary disease) in older adults have high case fatality rates due to lack of access to health care.

Global Pattern of Death
Mortality in Afghanistan & Russia

  • The crude annual death rate in Afghanistan (nearly 20 per 1,000) reflects a war-torn impoverished population with little access to health care.
  • Annual death rates are also high in the Russian Federation (15 per 1,000) likely due to high rates of alcohol abuse and smoking.

Figure 1.10 Global Death Rates, 2006

Figure 1.11 Deaths from Disease Worldwide, 2009

Epidemiologic Transition

  • Many nations are experiencing marked increases in life expectancy and decreases in fertility.
  • This “demographic transition” has produced populations with a relative abundance of geriatric individuals compared to younger people.
  • These demographic changes have occurred in concert with a closely related phenomenon called the “epidemiologic transition”.

Epidemiologic Transition

  • The “epidemiologic transition” is the transition from acute infectious, parasitic and nutritional deficiency diseases as the predominant causes of morbidity and mortality to a predominance of noninfectious chronic diseases.

Causes of Death in High Versus Low Income Nations

  • Approximately 75% of deaths in high income nations are attributable to chronic diseases (heart disease, cancer, stroke, COPD, diabetes).
  • In contrast, nearly 60% of deaths in low income nations are due to acute conditions (infection, violence, perinatal and maternal disease).

Figure 1.12 Relative Mortality Rates for High Income Nations

Figure 1.13 Relative Mortality Rates for Low Income Nations

Deaths By Income Strata

  • More than five billion people (about 75% of the world population) reside in low income nations.
  • These populations exist on less than $3 US per person per day and have little or no access to clean water, proper sanitation and sewer systems, adequate nutrition and health care.
  • In low income nations, deaths from acute diseases exceed deaths from chronic diseases (13.9 versus 12.2 million in 2009).
  • In all other income strata, deaths from chronic diseases far exceed deaths from acute diseases.

Figure 1.14 Worldwide Deaths by Major Cause and National Income, 2008

Global Tobacco Smoking

  • Worldwide, approximately 40% of men and 10% of women are chronic smokers.
  • Smoking prevalence exceeds 40% in men of W. Pacific, S.E. Asia & European populations.
  • Smoking prevalence exceeds 20% in women of American and European populations.
  • A startling global statistic is that about 1 in 3 adults is a chronic smoker.

Figure 1.15 Worldwide Smoking Prevalence: 2005

Global Deaths From Smoking

    • Worldwide, 5.4 million people died from smoking-related diseases in 2009.
    • These included 1.6 million deaths from lung cancer, 1.5 million deaths from heart disease, 900,000 deaths from COPD, 650,00 deaths from other cancers and 500,000 deaths from stroke.

 

Figure 1.16 Worldwide Deaths Attributable to Cigarette Smoking, 2009

Global Obesity

  • Adults with Body Mass Index (BMI) of 30 or more are classified as obese.
  • Approximately 10% of men and 12% of women are obese in the world population.
  • Worldwide, more than 400 million people are obese.
  • The highest levels of obesity are observed in America & Europe (about 25% in women and 20% in men).
  • The global increase in obesity reflects a pandemic of over-nutrition and metabolic overload.

 

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Figure 1.17 Worldwide Obesity Prevalence: 2005

Obesity & Chronic Disease

  • Obesity increases the risk of several chronic diseases including hypertension, myocardial infarction, congestive heart failure, stroke, chronic arthritis, type 2 diabetes, gall bladder disease, gastro-esophageal reflux disease and several cancers.
  • Gravid obesity (BMI > 40) increases all cause mortality more than two-fold in both men and women.

Figure 1.18 Obesity and Risk of Disease

Relative Mortality in Children

  • Among the ten million children under 5 years of age who die annually, six million (60%) succumb to conditions attributable to malnutrition and starvation.
  • Pneumonia and diarrhea kill 3.8 million children under 5 years of age annually.
  • Globally, 37% of deaths among children under 5 years of age occur in the first month of life, most in the first week.

Figure 1.19 Relative Mortality Associated with Malnutrition and Underweight in Children

Body Mass & Disease

  • Body Mass Index (or Quetelet Index) is defined as weight in kilograms divided by (height)2 in meters, BMI = kg wt / (m ht)2.
  • The BMI has value as a continuous variable that reflects disease versus health.
  • Mortality stratified by BMI plots as a “U-curve”.
  • Low BMI values are associated with nutritional deficiencies and high BMI values with nutritional excesses.

Figure 1.20 Body Mass Index & Mortality Window of Homeostasis

Disability-Adjusted Life Years (DALY)

  • Disability-Adjusted Life Years (DALY) is a measure of overall disease burden, expressed as the number of years lost due to ill-health, disability or early death.
  • The DALY quantifies mortality and morbidity in a single, common metric.
  • The population DALY for a disease is calculated as the sum of the Years of Life Lost (YLL) due to premature mortality and the Years Lost due to Disability (YLD) for incident cases:

DALY = YLL + YLD.

 

Disability-Adjusted Life Years (DALY)

  • In 2004, the average DALY across all WHO regions was 237 per 1,000 persons, of which about 60% was due to years of life lost from premature death, and 40% due to years of healthy life lost due to disability from non-fatal diseases.
  • In the nations of sub-Saharan Africa, the DALY are more than twofold higher than the rest of the world, largely due to high mortality rates from both acute and chronic conditions.
  • Higher than average DALY are also evident in the war torn nations of Afghanistan and Iraq.

Figure 1.21 Disability Adjusted Life Years, 2004

Global DALY Pattern

  • In regions with the highest DALY, premature deaths account for more than two thirds of the DALY, whereas in more developed nations, premature deaths and disability each account for roughly half of the disease burden.
  • This pattern reflects the impact of the epidemiologic transition, vis a vis., the greater disease burden of communicable diseases and maternal, perinatal and nutritional conditions in developing nations compared to the non-communicable diseases that are more prominent in developed nations.

Figure 1.22 DALY, YLL and YLD by Region

Prevention

  • Four major groups of chronic diseases, cardiovascular diseases, cancers, chronic respiratory diseases and diabetes represent the greatest burden to human health.
  • These four disease groups are the world’s biggest killers, causing an estimated 36 million deaths each year and approximately 60% of all deaths globally.
  • Fortunately, these diseases are largely preventable by eliminating shared risk factors, mainly tobacco addiction, unhealthy diet and obesity, sedentary lifestyle and the harmful use of alcohol.

Conclusions

  • Many nations are experiencing marked increases in longevity (life expectancy) and decreases in fertility.
  • These demographic changes have occurred in concert with the epidemiologic transition, the transition from acute infectious, parasitic and nutritional deficiency diseases to noninfectious chronic diseases that are now the main causes of morbidity and mortality worldwide.

Conclusions

  • Four chronic disease groups (cardiovascular disease, cancer, chronic obstructive pulmonary disease and diabetes) account for 60% of all deaths.
  • On a global basis, it is therefore necessary to raise the priority accorded to chronic diseases and develop and implement effective disease prevention and health promotion strategies and policies for the populations at risk.