Non-communicable Disease & Prevention

Introduction: The Global NCD Burden

Non-communicable diseases (NCDs) — principally cardiovascular disease (CVD), type 2 diabetes mellitus (T2DM), cancer, and chronic obstructive pulmonary disease (COPD) — are responsible for approximately 74% of all global deaths annually. In Aotearoa New Zealand, NCDs account for the overwhelming majority of mortality and a large portion of health system expenditure. Crucially, a substantial proportion of NCD burden is preventable through modification of shared risk factors: tobacco use, harmful alcohol use, physical inactivity, and unhealthy diet.

The Four Major NCDs and Shared Risk Factors

Cardiovascular disease (CVD): the leading cause of death globally. Encompasses coronary artery disease (CAD), stroke, peripheral arterial disease, and heart failure. Modifiable risk factors: hypertension, dyslipidaemia, diabetes, smoking, obesity, physical inactivity. Non-modifiable: age, sex, family history, ethnicity. In NZ, Māori and Pacific people have significantly higher CVD mortality at younger ages than NZ European — a major health equity issue.

Type 2 diabetes mellitus (T2DM): characterised by insulin resistance and progressive beta-cell dysfunction. Closely linked to obesity (especially central adiposity), physical inactivity, and genetic predisposition. T2DM is itself a major risk factor for CVD, chronic kidney disease, blindness (diabetic retinopathy), and lower limb amputation (diabetic neuropathy and vasculopathy). NZ has one of the highest rates of T2DM among OECD countries; Māori and Pacific populations bear a disproportionate burden.

Cancer: the second leading cause of death in NZ. Key cancers by burden: colorectal, lung, breast, prostate, melanoma. Tobacco is responsible for ~20% of all cancer deaths worldwide (lung, oral cavity, bladder, kidney, cervix, oesophagus). Other modifiable risk factors: alcohol (oral, pharyngeal, oesophageal, liver, breast), obesity, physical inactivity. Māori have higher cancer incidence and significantly worse cancer survival than NZ European for most cancers — screening uptake, access to treatment, and stage at diagnosis are all contributing factors.

COPD: defined as persistent airflow limitation, most commonly caused by tobacco smoking (>80% of cases in high-income countries) and in lower-income settings also by indoor air pollution (biomass fuels). Characterised by progressive dyspnoea, chronic productive cough, and exacerbations. Second leading cause of preventable death globally.

Primary, Secondary, and Tertiary Prevention

The three levels of prevention provide a framework for NCD control:

Primary prevention: action taken before disease onset to prevent it occurring. Aims to reduce incidence. Examples: vaccination (HPV vaccine preventing cervical cancer), tobacco taxation and restrictions reducing smoking uptake, healthy food environments, exercise promotion, road safety.

Secondary prevention: early detection of disease before symptoms appear, to interrupt or slow progression. Aims to reduce prevalence by shortening disease duration or preventing complications. The key tool is screening — systematic testing of asymptomatic individuals at risk. Examples: breast screening mammography, cervical smear testing, bowel cancer screening, blood pressure measurement, fasting glucose testing for T2DM.

Tertiary prevention: management of established disease to prevent complications, disability, and premature death. Aims to reduce consequences of disease. Examples: cardiac rehabilitation post-MI, tight glycaemic control in T2DM to prevent retinopathy, inhaled corticosteroids in asthma/COPD to prevent exacerbations, antihypertensive therapy to prevent stroke recurrence.

The three levels are complementary — an effective NCD strategy requires investment at all three levels, with primary prevention being most cost-effective at population scale.

NZ Tobacco Control

Tobacco is the single leading preventable cause of death in NZ, killing approximately 5,000 New Zealanders per year. Māori smoking rates are substantially higher than the general population, contributing to inequities in CVD, COPD, and cancer.

NZ has a comprehensive tobacco control strategy:

• Taxation: NZ tobacco excise tax is among the highest in the world; price increases have been the most effective single intervention for reducing smoking, particularly among youth and low-income smokers
• Smokefree environments: indoor public places, workplaces, outdoor dining areas, public transport
• Plain packaging and graphic health warnings: mandated since 2018 (following Australia 2012)
• Cessation support: Quitline, nicotine replacement therapy (NRT) subsidised on Pharmac, varenicline (Champix/Chantix), and combination approaches
• Nicotine vaping products (e-cigarettes): regulated as a cessation tool; sold only in dedicated vape stores from 2023; age-restricted

The Smokefree Aotearoa 2025 goal (now extended to 2027 under the current government) aims to reduce smoking prevalence to <5% in all population groups, with a focus on eliminating the Māori-NZ European smoking rate gap. Key legislative change: the Smokefree Environments and Regulated Products (Smoked Tobacco) Amendment Act 2022 included a tobacco free generation provision (no person born after 2008 to ever legally purchase smoked tobacco products) and plans for radical reduction in nicotine content and retail outlet numbers — partially repealed by the incoming 2023 government, with the focus returned to vaping as cessation and denicotinisation.

NZ Screening Programmes

Population-based screening must meet the Wilson-Jungner criteria (WHO, 1968): the condition should be an important health problem; there should be a recognised latent or early symptomatic stage; there should be a suitable test; acceptable treatment should be available; the cost of case finding should be economically balanced; and case finding should be a continuing process.

BreastScreen Aotearoa: biennial mammography screening for women aged 45–69. Sensitivity ~70–85% for detection of invasive breast cancer. Māori and Pacific women have lower uptake and more advanced stage at diagnosis — targeted outreach is funded. Discussion point: the benefits (reduced breast cancer mortality) must be weighed against harms (false positives, overdiagnosis, anxiety, unnecessary biopsy).

National Cervical Screening Programme (NCSP): regular cervical smears (Pap smears → now HPV primary testing from 2023) for people with a cervix aged 25–69. HPV testing has higher sensitivity than cytology for detecting precancerous lesions (CIN2/3). The 9-valent HPV vaccine (Gardasil 9) for school-age children is complementary. Māori women have historically had higher cervical cancer rates and lower screening uptake.

National Bowel Screening Programme (NBSP): biennial faecal immunochemical test (FIT) for adults aged 60–74. Detects occult blood from adenomas or colorectal cancer. Positive FIT leads to colonoscopy. Has been shown to reduce colorectal cancer mortality by ~25% in eligible populations. Being rolled out nationally.

Absolute vs Relative Risk Reduction: Clinical and Epidemiological Concepts

Understanding risk reduction measures is essential for communicating prevention messages:

Relative risk reduction (RRR): the proportional reduction in risk in the treatment/intervention group compared to the control. RRR = (Risk_control − Risk_treatment) / Risk_control.

Absolute risk reduction (ARR): the actual numerical difference in risk. ARR = Risk_control − Risk_treatment.

Number needed to treat (NNT): NNT = 1/ARR — the number of people who must receive the intervention for one person to benefit.

Example: if statins reduce 5-year CVD event rate from 5% to 3.5% in a high-risk group: RRR = (5−3.5)/5 = 30%; ARR = 1.5%; NNT = 1/0.015 = 67. This means for every 67 patients treated with statins for 5 years, one CVD event is prevented. Understanding both RRR and ARR is important: drug company marketing often emphasises RRR (sounds more impressive) while ARR and NNT provide a more clinically meaningful picture of absolute benefit.