Leptin is a peptide hormone that is involved in a negative feedback circuit to decrease appetite and increase energy expenditure in response to fat accumulation. Leptin is synthesised in adipocytes but binds to receptors in the hypothalamus where it stimulates the release of the anorexigenic peptides proopiomelanocortin and corticotrophin releasing hormone, and inhibits the release of orexigenic peptides neuropeptide Y and agouti related peptide. The physiological actions of leptin are not completely understood. However, dysfunction of the normal leptin signal, via down-regulation of the receptors, appears to play a role in weight gain. Because leptin may play a role in the development of obesity, researchers are interested in the association between leptin levels and anthropometric measurements. In addition little is known about variations in leptin levels between the different ethnic groups.
Researchers1 have investigated the associations between serum leptin levels and various anthropometric measurements in US citizens. Within a representative sample, the mean serum leptin levels was significantly higher in women (12.7 µg/L) compared to men (4.6 µg/L). The researchers also used a multivariate analysis to show that serum leptin levels were associated with the sum of 4 skin fold measurements (triceps, subscapula, suprailiac and thigh), both waist and hip circumferences, ethnicity and age. These factor explained most of the variance in leptin concentrations in both men and women. Controlling for these anthropometric measurements showed that serum leptin levels in blacks was higher (6 to 8%) than whites in both sexes, whereas Mexican Americans has leptin levels between the two. Tricep skin fold thickness was almost as highly associated with serum leptin levels as the sum of the four skin fold thicknesses.
These results suggest that there is an ethnic variation in serum leptin levels, which is something that has not been extensively researched. This ethnic difference in leptin levels is reflected in the variation seen in the rates of obesity amongst black, white and Hispanic American citizens. Previous research has shown that the prevalence of whites with a body mass index over 27.3 kg/m2 is 34%, whereas for blacks it is 52%, and Mexican Americans it is 50%. Higher serum levels of leptin are associated with weight gain, because as the leptin receptor down regulates, leptin shows a compensatory rise. Whether these differences represent genetic variation, or dietary and lifestyle differences is not known. Anthropometric measurements appear to be accurate predictors of serum leptin levels, if ethnic background, age and sex are taken into consideration.
RdB
