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PA12.1-3 | Environmental & Nutritional Diseases — SDL Guide (Part 3)

Metabolic Syndrome — Criteria and Consequences

Metabolic syndrome is a cluster of cardiometabolic risk factors that frequently co-occur due to their shared driver: visceral adiposity and insulin resistance.

Diagnostic criteria (IDF 2006 / modified ATP III):
Central obesity (waist ≥90 cm men / ≥80 cm women in South Asians) PLUS any two of:

Component	Cut-off
Raised triglycerides	≥150 mg/dL (or on treatment)
Reduced HDL cholesterol	<40 mg/dL (men), <50 mg/dL (women)
Raised blood pressure	≥130/85 mmHg (or on treatment)
Raised fasting glucose	≥100 mg/dL (or diagnosed T2DM)

Pathophysiological unifier: visceral fat → excess free fatty acids → hepatic dyslipidaemia (↑TG, ↓HDL) + insulin resistance (↑glucose) + RAAS activation and sympathetic overactivity (↑BP).

Systemic consequences of obesity and metabolic syndrome:

Type 2 Diabetes Mellitus — insulin resistance → β-cell failure → hyperglycaemia
Atherosclerosis / cardiovascular disease — dyslipidaemia, hypertension, and systemic inflammation accelerate plaque formation; metabolic syndrome confers 2–3× CV risk
Non-alcoholic fatty liver disease (NAFLD) → steatohepatitis (NASH) → cirrhosis — driven by excess free fatty acids and insulin resistance
Obstructive sleep apnoea (OSA) — fat deposition in pharyngeal tissues; OSA further worsens insulin resistance
Cancer risk — colorectal, endometrial, breast (post-menopausal), renal, oesophageal adenocarcinoma; mechanisms: hyperinsulinaemia (↑IGF-1), adipokine signalling, chronic inflammation
Polycystic ovary syndrome, hyperuricaemia/gout, osteoarthritis (mechanical load)

A three-panel medical diagram showing metabolic syndrome diagnostic criteria, the visceral fat and insulin resistance mechanism, and major systemic consequences including diabetes and cardiovascular disease. — **Panel A:** Central obesity, South Asian waist cut-offs, raised triglycerides, reduced HDL cholesterol, raised blood pressure, raised fasting glucose, diagnosis rule: central obesity plus any two criteria. **Panel B:** Visceral adipocytes, excess free fatty acids, portal circulation, liver, hepatic dyslipidaemia, insulin resistance, RAAS activation, sympathetic overactivity, increased blood pressure. **Panel C:** Type 2 diabetes mellitus, beta-cell failure, hyperglycaemia, atherosclerotic plaque, cardiovascular disease, systemic inflammation, endothelial dysfunction, 2-3x cardiovascular risk.

SELF-CHECK

A 44-year-old man has a waist circumference of 96 cm, fasting glucose 108 mg/dL, triglycerides 190 mg/dL, HDL 36 mg/dL, and blood pressure 136/88 mmHg. Which ONE adipokine is PARADOXICALLY LOW despite his increased fat mass and most contributes to his insulin resistance?

A. Leptin

B. TNF-α

C. Resistin

D. Adiponectin

Reveal Answer

Answer: D. Adiponectin

This patient meets criteria for metabolic syndrome (central obesity + all 4 other criteria present). Adiponectin is the key anti-inflammatory, insulin-sensitising adipokine that is paradoxically LOW in obesity — its loss removes an important brake on insulin resistance and inflammation. Leptin is HIGH in obesity (though functionally ineffective due to resistance). TNF-α and resistin are pro-inflammatory adipokines that are elevated in obesity and worsen insulin resistance, but the 'paradoxically low despite high fat mass' clue specifically points to adiponectin.

Linking Environmental and Nutritional Disease: A Synthesis

A four-panel pathology synthesis diagram links environmental and nutritional exposures to chronic low-grade injury, latency, tissue vulnerability, and later clinical disease. — **Panel A:** Shared timeline showing sustained exposure, chronic low-grade injury, oxidative stress, inflammation, DNA damage, metabolic overload, tissue vulnerability, and clinical disease.. **Panel B:** Adult lung and airway showing air pollution and tobacco smoke exposure, alveolar inflammation, reactive oxygen species, epithelial DNA damage, malignant nodule, and 20-30 year latency.. **Panel C:** Child silhouette showing protein-calorie malnutrition with developing brain injury, liver change, muscle wasting, skin and hair changes, and rapid injury in growing tissues.. **Panel D:** Adult abdominal cross-section showing visceral adiposity, insulin resistance, fatty liver/NAFLD progression over 10 years, and colorectal cancer risk over 20 years..

The three PA12 competency areas share a common pathological theme: chronic low-grade injury from sustained exposure.

Air pollution and tobacco cause decades-long oxidative stress, inflammation, and DNA damage before clinical disease appears — the latency between first cigarette and lung cancer is typically 20–30 years.
Protein-calorie malnutrition causes accelerated morphological changes in actively growing tissues — the child's developing brain, liver, and skin are the earliest casualties.
Obesity and metabolic syndrome represent a sustained metabolic overload — the same visceral adiposity that causes insulin resistance today causes NAFLD in 10 years and colorectal cancer in 20.

Recognising the time scale of these exposures is as important as knowing the pathological endpoint — it is the foundation of both primary prevention counselling and early diagnosis.