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Leptin

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Leptin is a hormone produced by fat tissue (adipocytes) that regulates metabolism, neuroendocrine function, and energy balance. It plays a crucial role in appetite control, weight regulation, and metabolic health.

Leptin is a key clinical marker in the diagnosis of type 2 diabetes, ischemic heart disease, obesity, and secondary amenorrhea. It serves as a signal of energy reserves, with its concentration increasing after meals, leading to reduced appetite.
 

Functions of Leptin

  • Regulates energy storage – Signals the brain to stop eating when fat stores are sufficient.
  • Controls appetite – Inhibits the hunger-promoting hormone ghrelin.
  • Influences metabolic rate – Higher leptin levels promote energy expenditure.
  • Plays a role in reproduction – Low levels can lead to amenorrhea and infertility.
  • Affects stress response – Modulates cortisol and other stress hormones.

    Leptin Deficiency and Resistance

    1. Genetic Leptin Deficiency (Rare)

  • Caused by mutations in the leptin gene.
  • Leads to constant hunger and early-onset obesity.
  • Associated with hypothyroidism, hypogonadism, and delayed puberty.

  • 2. Leptin Resistance (Common in Obesity)

  • High leptin levels, but the brain does not recognize satiety signals.
  • Results in overeating, weight gain, and metabolic disorders.
  • Linked to type 2 diabetes, cardiovascular disease, and insulin resistance.
     

    Effects of Leptin on the Body

  • Fasting (8–14 hours) before the test.
  • Avoid physical and emotional stress for 72 hours before the test.
  • Limit alcohol intake for several days before testing.
  • Do not smoke for at least 1 hour before the test.
  • Suspected genetic leptin deficiency (early-onset severe obesity).
  • Difficulties in weight gain or loss.
  • Reproductive dysfunction due to improper nutrition or excessive exercise.
  • Assessment of cardiovascular disease risk factors.
  • Differential diagnosis of type 2 diabetes and obesity

Interpretation of Leptin Levels

Elevated Leptin Levels

  • Obesity – Increased fat mass leads to higher leptin production.
  • Type 2 Diabetes (Non-Insulin-Dependent Diabetes Mellitus, NIDDM) – Leptin resistance is common in diabetic patients.
  • Persistent Hunger (Hyperphagia) – Due to leptin resistance, the brain does not recognize satiety signals, leading to overeating.

Reduced Leptin Levels

  • Loss of Appetite (Anorexia or Starvation) – Low energy reserves reduce leptin production.
  • Weight Loss – Leptin decreases as fat stores shrink.
  • Obesity (Due to Genetic Leptin Deficiency) – Individuals with congenital leptin deficiency do not produce enough leptin, leading to uncontrolled hunger and severe obesity from early childhood.