Role of obesity and leptin in the pubertal process and pubertal growth--a review.

The prevalence of obesity is increasing alarmingly to epidemic proportions in children and adolescents, especially in industrialized countries. The finding that overweight children, especially girls, tend to mature earlier than lean children has led to the hypothesis that the degree of body fatness may trigger the neuroendocrine events that lead to the onset of puberty. Obese children have high leptin levels, and these may play a role in their earlier onset of puberty. Leptin receptors have been identified in the hypothalamus, gonadotrope cells of the anterior pituitary, and ovarian follicular cells, as well as Leydig cells. Leptin accelerates gonadotropin-releasing hormone (GnRH) pulsatility in hypothalamic neurons, and it has a direct effect on the anterior pituitary. Leptin administration at low doses may have a permissive, threshold effect on the central networks that regulate gonadotropin secretion. However, at high levels, such as those in obese people, it can have an inhibitory effect on the gonads. Children with obesity also have increased adrenal androgen levels, which may be involved in the accelerated growth of these children before puberty. Recent data indicate that leptin has a specific role in stimulating the activity of enzymes essential for the synthesis of adrenal androgens. Children with exogenous obesity frequently show an increase in height velocity with tall stature for age despite low growth hormone levels. Our group has shown that leptin acts as a skeletal growth factor, with a direct effect on skeletal growth centers, in the mice mandibular condyle, a model of endochondral ossification. In summary, obesity is associated with early puberty. Elevated leptin levels might have a permissive effect on the pubertal process and pubertal growth.