1. Patterns in Health and Disease: Epidemiology and Physiology

2. Objectives Define or describe the science of epidemiology.
Contrast infectious with degenerative diseases as causes of death.
Identify three major categories of risk factors and examples of specific risk factors in each.
Compare the epidemiologic triad with the web of causation as models to study infectious and degenerative disease, respectively.

3. Objectives
Describe the difference between primary and secondary risk factors for coronary heart disease (CHD).
Describe the steps an epidemiologist must follow to show that a risk factor is causally connected to a disease.
Describe the hypothesis linking resistance to insulin as a cause of hypertension.

4. Outline Epidemiology Coronary Heart Disease Physiology Synthesis
Physical Inactivity as a Risk Factor
Physiology
Synthesis

5. Epidemiology
Epidemiology
The study of the distribution and determinants of health states and the use of this information in the control of disease
Uses of epidemiology:
Establish the cause of disease
Trace the natural history of disease
Describe the health status of populations
Evaluate an intervention
Epidemiologic triad
Shows connections between the environment, agent, and host that cause disease

6. The Epidemiologic Triad
Epidemiology
The Epidemiologic Triad
Figure 14.1

7. Disease Control Destroying or removing the agent at its source
Epidemiology
Disease Control
Destroying or removing the agent at its source
Altering the environment to reduce transmission of the agent
Improving the host’s resistance to the agent
Altering the host’s behaviors
Improved nutrition
Immunization
Exercise

8. Epidemiology
In Summary
Epidemiology is the study of the distribution and determinants of health states and the use of this information in the control of disease.
Disease control can be achieved by: (1) destroying or removing the agent at its source, (2) altering the environment to reduce transmission of the agent, or improving the host’s resistance to the agent, and (3) altering the host’s behaviors such as improved nutrition, immunization, and exercise.

9. Infectious and Degenerative Diseases
Epidemiology
Infectious and Degenerative Diseases
Infectious diseases
Tuberculosis
Pneumonia
Chronic (degenerative) diseases
Cancer, heart disease, and stroke
Responsible for 56% of all deaths in U.S. in 2004
Difficult to establish cause of disease
Due to genetic, environmental, and behavioral factors

10. Web of Causation Difficult to establish the cause of chronic diseases
Epidemiology
Web of Causation
Difficult to establish the cause of chronic diseases
Atherosclerosis
Complex involvement of factors
Risk factors
Genetic
Gender, race
Environmental
Access to high-fat foods, places to exercise
Behavioral
Diet
Smoking
Physical activity/inactivity

11. Web of Causation: Titanic Disaster
Epidemiology
Web of Causation: Titanic Disaster
Figure 14.2

12. Web of Causation: Atherosclerosis
Epidemiology
Web of Causation: Atherosclerosis
Figure 14.3

13. Major Risk Factor Categories
Epidemiology
Major Risk Factor Categories
Figure 14.4

14. Degenerative Diseases
Epidemiology
Degenerative Diseases
Result from interaction of genetics and environment
Inherited/biological factors
Age, gender, race, ease of developing disease
Cannot be changed
Environmental and behavioral risk factors
Most susceptible to change
Importance of personal responsibility

15. A Closer Look 14.1 Leading and Actual Causes of Death
Epidemiology
A Closer Look 14.1 Leading and Actual Causes of Death
Leading causes of death
Heart disease
Cancer
Stroke
Chronic lung disease
Unintentional injuries
Diabetes
Actual causes of death
Tobacco
Diet and physical inactivity
Alcohol consumption
Infection
Toxic agents
Motor vehicles
Firearms

16. Epidemiology
In Summary
Epidemiologists show that the major causes of death in the United States are degenerative diseases such as heart disease and cancer. The development and progress of these diseases are affected by the interaction of environmental and behavioral risk factors.

17. Coronary Heart Disease (CHD)
Associated with atherosclerosis
Thickening of the inner lining of arteries
Contributor to heart attack and stroke death
Diseases of the heart and blood vessels are the leading cause of death in the U.S.
Associated with risk factors
Each risk factor magnifies the risk of CHD
Eliminating a risk factor causes a reduction in risk

18. A Closer Look 14.2 Risk Factors for Coronary Heart Disease
Primary
Increases risk of CHD in and of itself
Secondary
Increases risk of CHD if primary risk factor is present
Negative risk factor
Reduces risk of CHD
HDL-C
Some can’t be changed
Some can be changed

19. A Closer Look 14.2 Risk Factors for Coronary Heart Disease
Can’t be changed
Heredity
Gender
Age
Race
Can be changed
Cigarette smoking
High serum cholesterol
High blood pressure
Physical inactivity
Blood glucose
Obesity
Stress

20. Coronary Heart Disease
In Summary
Risk factors can be divided into three categories: genetic/biological, environmental, and behavioral.
The risk factors of smoking, high cholesterol, and hypertension interact to magnify the risk of CHD. Similarly, elimination of one of them causes a disproportionate reduction in the risk of CHD.

21. Determining Association Between Risk Factor and Disease
Physical Inactivity as a Risk Factor
Determining Association Between Risk Factor and Disease
Temporal Association
Plausibility
Consistency
Strength of association (relative risk)
Dose-response relationship
Reversibility
Study design
Judging the evidence

22. Physical Inactivity as a Risk Factor
Independent risk factor for CHD
Relative risk of CHD due to inactivity is similar to other risk factors
Smoking
High cholesterol
High blood pressure
High population attributable risk
Percentage of population at risk
Due to large number of inactive individuals

23. U.S. Population at Risk Physical Inactivity as a Risk Factor
Figure 14.5

24. In Summary Physical inactivity is an independent risk factor for CHD.
Physical Inactivity as a Risk Factor
In Summary
Physical inactivity is an independent risk factor for CHD.
The relative risk of CHD due to inactivity (1.9) is similar to that of hypertension (2.1) and high cholesterol (2.4). The fact that about 59% of the population is inactive indicates the enormous impact a change in physical activity habits can have on the nation’s risk for CHD.

25. Hypertension Often occurs with other metabolic abnormalities
Physiology
Hypertension
Often occurs with other metabolic abnormalities
Abdominal obesity
Peripheral insulin resistance
Dyslipidemia
High triglycerides
Metabolic syndrome
Coexistance of these risk factors

26. Metabolic Syndrome Insulin resistance
Physiology
Metabolic Syndrome
Insulin resistance
Reduced ability of peripheral tissues to take up glucose
Leads to hyperinsulinemia
Due to higher insulin secretion by pancreas
Also increases FFA level in the blood
Together with abdominal obesity
Hyperinsulinemia associated with:
Increased SNS activity
Increased sodium and water retention
Increased smooth muscle proliferation in blood vessels

27. The Insulin-Resistance and Hypertension Hypothesis
Physiology
The Insulin-Resistance and Hypertension Hypothesis
Figure 14.6

28. What Causes the Metabolic Syndrome?
Physiology
What Causes the Metabolic Syndrome?
Several competing hypotheses
Insulin resistance
Changes in blood vessels and water retention cause hypertension
Hypertension
Decrease in small blood vessels reduces glucose and insulin delivery to muscle, causing insulin resistance
Increased SNS activity
Increases blood pressure and blood glucose
Obesity
Adipose tissue secretions affect insulin resistance

29. A Closer Look 14.3 The Metabolic Syndrome—Is It a Real Syndrome?
Physiology
A Closer Look 14.3 The Metabolic Syndrome—Is It a Real Syndrome?
Reasons for this question:
Only half to two-thirds of people diagnosed with metabolic syndrome have insulin resistance
Both hypertension and dyslipidemia can exist without obesity or insulin resistance
However:
Diagnosis helps direct lifestyle changes
Classification as a disease allows insurance coverage

30. Definition of the Metabolic Syndrome
Physiology
Definition of the Metabolic Syndrome
Three or more of the following risk factors:
Abdominal obesity
Waist circumference >102 cm (men) and >88 cm (women)
Hypertriglyceridemia
≥150 mg/dl
Low HDL cholesterol
<40 mg/dl (men) and <50 mg/dl (women)
High blood pressure
≥130/85 mmHg
High fasting blood glucose
≥110 mg/dl

31. Prevalence of the Metabolic Syndrome
Physiology
Prevalence of the Metabolic Syndrome
Overall, 23.7% of the population
6.7% in those 20–29 years of age
40% in those >60 years of age
Highest in Mexican-Americans
31.9% of that population

32. A Closer Look 14.4 Overweight and Obesity
Physiology
A Closer Look 14.4 Overweight and Obesity
Prevalence in US adults
66.3% are overweight (BMI = 25.0–29.9 kg/m2)
32.2% are obese (BMI ≥30.0 kg/m2)
Prevalence in children and adolscents
16% females and 18.2% males overweight
Linked to rise in diabetes
Recommendations for control of overweight and obesity
Surgeon General “Call to Action”
Healthy People 2010
2005 Dietary Guidelines for Americans

33. Physiology
In Summary
The metabolic syndrome model describes the potential causative connections between and among obesity, peripheral insulin resistance, hypertension, and dyslipidemia.
The insulin resistance is located primarily in skeletal muscle, being greater in type II muscles with their limited capillary supply.
Exercise can both directly and indirectly decrease the risk of CHD by influencing obesity, insulin resistance, and hypertension.

34. Healthy People 2010 Nutrition objectives Physical activity objectives
Synthesis
Healthy People 2010
Nutrition objectives
Achieve a healthy body weight
Eat <30% total calories from fat and <10% total calories from saturated fat
Eat at least five servings of fruits and vegetables and six servings of grains daily
Physical activity objectives
Engage in any leisure-time activity
Participate in sustained activity for at least 30 minutes daily
Engage in activity that promotes cardiovascular fitness three or more days per week for 20 minutes or more per occasion
Participate in activity to enhance strength and flexibility

35. Study Questions
There is a sudden increase in the number of birth defects in one section of a large city. Describe what an epidemiologist might do to determine what is causing this problem.
Why is a web of causation model needed to study the causes of degenerative diseases, in contrast to infectious diseases?
Physical inactivity was long considered only a secondary risk factor. What “proof” did investigators have to offer to convince the scientific community otherwise?
What is the difference between primary and secondary risks for coronary heart disease (CHD)? Why does a high-fat diet not appear as a risk factor for CHD?

36. Study Questions
Draw a diagram of the hypothesized connections between and among obesity, insulin resistance, hypertension, and dyslipidemia. Indicate the primary site of insulin resistance, and explain how exercise training might reduce the problem.