Epidemiology of NCDs

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NCDs Overview - The Silent Spread

  • Definition: Chronic, non-infectious, long-duration health conditions.
  • Major Types:
    • Cardiovascular diseases (CVDs)
    • Cancers
    • Chronic respiratory diseases (e.g., COPD, Asthma)
    • Diabetes
  • Global Burden: Account for ~74% of all deaths worldwide.
  • Indian Burden: Leading cause of death (>60%); significant premature mortality (deaths between 30-69 years).

⭐ NCDs are the leading cause of mortality and morbidity worldwide.

NCD Risk Factors - Culprits & Causes

  • Modifiable Behavioural Risk Factors:
    • Tobacco use (smoke/smokeless)
    • Unhealthy diet (↓fruits/veg, ↑salt/sugar/fats)
    • Physical inactivity
    • Harmful use of alcohol
  • Metabolic Risk Factors (Intermediate):
    • ↑ Blood pressure (Hypertension: ≥ 140/90 mmHg)
    • Overweight/Obesity (BMI ≥ 25 kg/m² / ≥ 30 kg/m²)
    • ↑ Blood glucose (Hyperglycemia)
    • ↑ Blood lipids (Hyperlipidemia)
  • Non-Modifiable Risk Factors:
    • Age
    • Sex
    • Genetics/Family history

These factors interact in a 'web of causation'.

⭐ The four major NCDs share four common behavioural risk factors: tobacco use, unhealthy diet, physical inactivity, and harmful use of alcohol.

Risk factors, metabolism, and aging in NCDs

Measuring NCD Burden - Stats & Stories

  • Prevalence: Existing cases at a point in time.
  • Incidence: New cases over a period.
  • Mortality Rates: Crude (overall), Specific (cause/group), Standardized (age-adjusted).
  • DALYs: Disability-Adjusted Life Years. $DALY = YLL + YLD$.

    ⭐ DALYs combine years of life lost (YLL) from premature mortality and years lived with disability (YLD).

  • QALYs: Quality-Adjusted Life Years; measures life quality & quantity.
  • Attributable Risk (AR): Excess risk in exposed. $AR = I_e - I_u$.
  • Pop. Attributable Risk (PAR): Proportion of disease in population due to exposure. $PAR = (I_p - I_u) / I_p$.
  • Rule of Halves: Hypertension: many unaware/undiagnosed/untreated/uncontrolled.
  • Data Sources: NSSO, NFHS, Cancer Registries, GBD study.

NCD Screening & Surveillance - Detect & Defend

  • Screening: Early NCD detection in asymptomatic individuals.
  • 📌 Wilson & Jungner's Criteria: Important problem; known history; detectable early; suitable test; accepted treatment; facilities; agreed policy; cost-effective; continuous.
  • Types:
    • Mass: Entire population.
    • High-risk/Selective: Specific risk groups.
    • Opportunistic: During routine visits.
  • Key Biases:
    • Lead time: Earlier diagnosis, not ↑survival.
    • Length time: Detects slow-growing cases.
    • Volunteer: Participants differ.
  • NCD Surveillance: Monitors trends, risk factors; guides policy.
  • India (NPCDCS): Screens for Diabetes, HTN, Oral, Breast, Cervical cancers.

⭐ Lead time bias can make a screening test appear to prolong survival when it only advances the time of diagnosis.

Lead time bias vs actual survival benefit in screening

Population Screening for Hypertension (Simplified)

NCD Prevention & Control - Action Against Ailments

  • Levels of Prevention:
    • Primordial: Prevent risk factor development (e.g., healthy public policies).
    • Primary: Modify risk factors (e.g., tobacco cessation, diet for pre-DM).
    • Secondary: Early detection & treatment (e.g., HTN/DM screening, Pap smear).
    • Tertiary: Limit disability, rehabilitation (e.g., post-stroke care, diabetic foot care).
  • Strategies:
    • Population-based: Targets whole community (e.g., salt reduction campaigns).
    • High-risk individual: Targets those at increased risk (e.g., statins for high CVD risk).
  • NPCDCS Focus: Health promotion, early diagnosis, management, infrastructure.
  • WHO 'Best Buys': Cost-effective (e.g., tobacco taxes, salt reduction, physical activity promotion, aspirin for CVD). Levels of Prevention Pyramid

⭐ Primordial prevention aims to prevent the development of risk factors in the first place, like promoting healthy lifestyles from childhood.

High‑Yield Points - ⚡ Biggest Takeaways

  • NCDs are India's leading cause of death; CVDs are most common.
  • Four major NCDs: Cardiovascular diseases, Diabetes, Cancers, Chronic Respiratory Diseases.
  • Key modifiable risk factors: tobacco, unhealthy diet, physical inactivity, harmful alcohol use.
  • Primordial prevention (preventing risk factor development) is crucial.
  • NPCDCS is the main Indian program for NCD prevention and control.
  • Rule of Halves indicates significant under-diagnosis and poor control of NCDs.
  • Iceberg phenomenon highlights many undiagnosed NCD cases in the community.
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Epidemiology of NCDs - Free Indian Medical PG Review