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Serum leptin level is associated with appetite and energy expenditure in healthy individuals. Leptin is produced primarily in fat cells and also in the placenta and probably in the stomach. Serum leptin concentrations are highly correlated with body fat content. These processes are stimulated by insulin, glucocorticoids, and tumor necrosis factor–alpha, another product of adipocytes. These observations suggest that leptin signals the brain about the quantity of stored fat.
Male: 0.5–12.7 ng/mL
Female: 3.9–30.0 ng/mL
Biomarker for body fat metabolism
Very low–calorie diet
Serum leptin concentrations increase with progressive obesity. The concentrations are higher in women than in men, for any measure of obesity, and they decrease with age in both women and men.
Pregnant women have higher serum leptin concentrations than nonpregnant women.
Serum leptin concentrations increase during childhood, with the highest concentrations in children who gain the most weight; higher serum leptin concentrations are associated with an earlier onset of puberty.
The concentrations are similar in normal subjects and patients of the same weight with type 2 DM.
There is a diurnal rhythm of serum leptin concentrations, the values being 20–40% higher in the middle of the night as compared with daytime. The peak shifts in parallel with shifts in the timing of meals.
Leptin production is strongly influenced by nutritional state. Overeating increases serum leptin concentrations by nearly 40% within 12 hours, long before any changes in body fat stores. Conversely, in both normal-weight and obese subjects, fasting reduces serum leptin concentrations by 60–70% in 48 hours.