Relationship of serum leptin concentration with age, gender, and biomedical parameters in healthy, non-obese subjects.

It is known that the circulating levels of leptin, the adipocyte hormone implicated in the control of energy balance, are correlated with fat body mass (FBM), although the influences of other physiological conditions are not fully understood. We investigated the relationships of serum leptin concentration with age, gender, and 36 hormone-metabolic parameters in a sample of a well defined healthy population (n=246; age range 20-93 years), and in subgroups of lean individuals according to their body mass index (BMI), within similar age range and gender distribution. Only insulin secretion (positively) and testosteronemia (negatively, in males) show direct correlations. The other relationships are not significant but throughout collaborating variables, such as serum lipids, especially through FBM, lean body mass (LBM) through insulin secretion, and gender through FBM. In males, LBM correlates with insulin secretions, s-IGF-1 and with s-testosterone. The relationship between insulin secretion and LBM persists up to advanced age. From the present study it may be concluded that the positive relationship of leptin with insulin secretion and the negative one with testosterone, indicate direct implications of leptin in insulin signaling, as well as in male sexual development. Finally, the fact that the amount of secreted insulin depends on LBM and the latter on testosterone and IGF-1, indicates the importance of muscle mass in the control of insulin secretion.