Definition of a Risk Factor A risk factor is any attribute, characteristic, or exposure that increases the likelihood of developing a disease or healt

1. Definition of a Risk Factor
   A risk factor is any attribute, characteristic, or exposure that increases the likelihood of developing a disease or health condition. Examples include smoking (for lung cancer), obesity (for cardiovascular disease), and high cholesterol (for heart disease).

2. Crude, Standardized, and Specific Disease Rates

   • Crude Rate: The total number of cases (or deaths) in a population without adjustments for other factors (e.g., age, sex).

   • Standardized Rate: A rate adjusted for factors like age to allow fair comparisons between populations with different demographic structures.

   • Specific Rate: The rate for a particular subgroup, such as age-specific mortality rates.

3. Prevalence vs. Incidence Rates

   • Prevalence: The proportion of a population that has a disease at a specific time (both new and existing cases).

   • Incidence: The number of new cases that develop in a given time period, usually per 1,000 or 100,000 people per year.

4. Epidemiological Research Designs (Characteristics, Advantages, Disadvantages)

   • Cross-sectional: Observes a population at one point in time. Pros: quick, inexpensive. Cons: cannot determine causality.

   • Cohort Study: Follows a group over time. Pros: identifies risk factors. Cons: expensive, time-consuming.

   • Case-Control Study: Compares people with a disease (cases) to those without (controls). Pros: efficient for rare diseases. Cons: recall bias.

   • Randomized Controlled Trial (RCT): Participants are randomly assigned to groups. Pros: best for causation. Cons: costly, ethical concerns.

5. Difference Between Prevalence and Incidence Cases

   • Prevalence includes all cases at a given time, while incidence only includes new cases during a specified time period.

6. Three Goals of Epidemiology

   • Identify causes and risk factors for diseases.

   • Determine the extent of disease in a population.

   • Develop preventive and control measures.

7. Relative Risk (RR) and Odds Ratio (OR)

   • Relative Risk (RR): The ratio of disease risk in an exposed group to a non-exposed group.

   • Odds Ratio (OR): The odds of disease in exposed vs. non-exposed groups (used in case-control studies).

8. Interpreting Relative Risk and 95% Confidence Interval (CI)

   • If RR = 1, no association exists.

   • If RR > 1, exposure increases risk.

   • If RR < 1, exposure reduces risk.

   • A 95% CI that does not include 1 means the result is statistically significant.

9. Confounders

   • A confounder is a variable that influences both the independent and dependent variables, leading to a false association.

   • Example: Coffee drinking is linked to lung cancer, but smoking (a confounder) explains the association.

10. Interaction Effect

• When the effect of one variable on an outcome depends on the level of another variable.

• Example: Exercise reduces heart disease risk, but the effect is stronger in non-smokers than smokers.

11. Mill’s Canons of Determining Causation

• Strength of association

• Consistency of findings

• Specificity

• Temporal sequence (cause precedes effect)

• Biological plausibility

Physical Activity (PA) Measures

12. Definition of MET (Metabolic Equivalent of Task)

• A MET is a unit measuring energy expenditure. 1 MET = energy used at rest, while higher MET values represent higher-intensity activities.

13. Methods to Measure Physical Activity and Caloric Expenditure

• Accelerometers: Measure movement intensity.

• Indirect Calorimetry: Estimates energy expenditure by measuring oxygen consumption and carbon dioxide production.

• Direct Calorimetry: Measures heat production in a metabolic chamber.

• Doubly Labeled Water: Gold standard for measuring energy expenditure over days/weeks using isotopes.

14. Definition of Sedentary Behavior

• Any activity with an energy expenditure ≤1.5 METs while sitting or reclining (e.g., watching TV, working at a desk).

15. Risk Factors for Osteoporosis

• Age, female sex, low calcium/vitamin D intake, smoking, excessive alcohol, inactivity, family history.

16. Age of Rapid Decline in Cardiorespiratory Fitness

• Around age 45–50.

17. Age Range for Peak Bone Mass in Women

• Between ages 25–30.

18. Definition of Ejection Fraction

• The percentage of blood ejected from the left ventricle during each heartbeat. A normal ejection fraction is 55–70%.

19. Respiratory Exchange Ratio (RER) and Substrate Oxidation

• RER = CO₂ produced / O₂ consumed.

• RER ~0.7: Fat oxidation dominant.

• RER ~1.0: Carbohydrate oxidation dominant.

• RER >1.0: Anaerobic metabolism.

20. Runner’s Health Study Findings

• Running is linked to lower mortality, reduced cardiovascular disease, and improved lifespan.

21. Physical Activity Prevalence by Gender, Ethnicity, and Region

• Men are generally more active than women.

• PA levels vary by ethnicity and region, with lower activity seen in the southeastern U.S.

All-Cause Mortality

22. Metabolic and Behavioral Risk Factors for All-Cause Mortality

• Metabolic: Obesity, diabetes, hypertension.

• Behavioral: Smoking, poor diet, inactivity.

23. Dose-Response Relationship Between PA and All-Cause Mortality

• More exercise is linked to lower mortality, with diminishing returns at higher levels.

24. Gender Differences in the Dose-Response Relationship

• Women may gain more longevity benefits per unit of exercise than men.

25. Harvard Alumni Study Findings

• 2,000+ kcal/week from PA is associated with a significant reduction in mortality risk.

26. Iowa Women’s Health Study Findings

• Physical activity reduces mortality risk, even in older women.

27. Swedish Twin Registry Study Findings

• Genetics and lifestyle both influence longevity, with PA playing a critical role.

28. Main Conclusion from the English and Scottish Health Survey Study

• Moderate activity significantly reduces mortality risk.

29. Cleveland Clinic Cohort Study Findings

• Higher cardiorespiratory fitness is associated with lower mortality risk across all ages.

30. Hours of Exercise per Week to Reduce Mortality Risk

• ~150–300 minutes per week of moderate-intensity activity (or ~75–150 minutes vigorous-intensity).

31. Fat vs. Fit Controversy and Implications

• Fitness matters more than body weight in predicting mortality risk.

• Overweight but active individuals have lower risk than lean but inactive individuals.

• Implications: Promoting PA should be a primary public health focus, even in those with higher BMI.This suggests that health interventions should prioritize physical activity and fitness levels rather than solely focusing on weight loss as a measure of health.