BMI-conditional standard of leptin serum values in children: proposal of a statistical procedure for the analysis of influencing variables.

In order to define serum leptin values in children, its concentration was assayed in 3,453 children, 5-14 years old, and body mass index (BMI) and pubertal development were recorded. Insulin, testosterone (in males) and 17beta-estradiol (in females), the sum of four skinfold thicknesses (SST), waist-to-hip ratio, and body fat mass were also determined in 1,601 children. Analysis of multicollinearity effects on estimated models demonstrated a quasi-linear correlation between SST and BMI, the former being prevalent. Although other variables were strongly correlated with leptin, assuming only SST as predictor, R2 yielded a value of 0.711 in males and 0.607 in females. When the other variables were added, R2 increased by about 0.03 in both sexes. BMI and SST were the most important of all the predictors and each can act as a sort of proxy for the others. When the z-scores of BMI of all 3,453 children were subdivided into deciles, any correlation with leptin was no more significant inside each BMI z-score range. This study demonstrates that subcutaneous fat mass may be considered the prevalent determinant factor. The adopted statistical procedure furnished results useful for reference values based on BMI z-score as a simple and appropriate evaluation for serum leptin concentrations in children.

Using obese-specific charts of height and height velocity for assessment of growth in obese children and adolescents during weight excess reduction.

OBJECTIVE: The influence of weight excess reduction on height and height velocity of obese subjects should be evaluated on the basis of appropriate standards, since the pattern of growth of obese subjects is different from that of normal weight subjects. DESIGN, SUBJECTS AND MEASUREMENTS: Height, weight and triceps skinfold thickness were recorded from 17987 school subjects (9256 males and 8731 females), 3-18 y of age, from three provinces of central Italy, and a growth reference curve of height was constructed. Using BMI (as computed using the tables of Rolland-Cachera et al) and triceps skinfold thickness, normal-weight subjects (NWS) and obese subjects (OS) were identified and specific reference curves (mean+/-s.d. every sixth month of age) were developed for both groups. Centiles of height were also calculated for OS. Various (2-4) measurements of height in school subjects were performed and a graph of height velocity (HV) was constructed in NWS and in OS using the JPPS method. The yearly mean +/-s.d. of HV was also calculated, based on square root transformed data (in order to realise a Gaussian distribution), deriving from successive measurements in total subjects, in NWS and in OS. The z-scores of height and of the square root of HV were calculated in 217 obese subjects (125 males and 92 females) before and during a weight excess reduction programme (WERP). Obese subjects in WERP who showed a reduction of z-score of BMI were considered as 'responsive'; those who either maintained or showed an increase of z-score of BMI were considered as 'non-responsive'. Obese subjects in WERP were followed for 1-4 y, giving the following results: 0-1 y, 142 responsives and 75 non-responsives; 0-2 y, 76 responsives and 33 non-responsives; 0-3 y, 35 responsives and 30 non-responsives; 0-4 y, 24 responsives and 18 non-responsives. RESULTS: Compared to NWS, OS showed a significantly greater HV in 4-9y males and in 4-8y females, but in older children the pubertal spurt was reduced and more precocious. As a result, the height of OS, which was greater in 3-13 year-old males and in 3-11.5 year-old females, subsequently showed a reduction, as compared to that of NWS, in 16-18 year-old males and in 13-18 year-old females. In both responsive and non-responsive groups of obese subjects in WERP, the z-scores of height showed a reduction during WERP when evaluated using the reference curve of the total school population. In contrast, when their growth was evaluated according to the obese-specific reference curve, no significant variation was observed comparing both z-scores before and during the WERP. CONCLUSIONS: More appropriate information on the growth of obese subjects may be obtained when evaluating the height and HV according to obese-specific reference standards from the same population of origin. Adopting this modality, no significant variation of height resulted during WERP in obese children.

Fasting serum leptin levels in the analysis of body mass index cut-off values: are they useful for overweight screening in children and adolescents? A school population-based survey in three provinces of central Italy.

OBJECTIVE: Body mass index (BMI) was determined in a population of school students from three provinces of central Italy. Fasting serum leptin concentrations were assayed in a large number of subjects from the same area, to determine their distribution as plotted against the standard deviation score (z-score) of BMI. DESIGN, SUBJECTS AND MEASUREMENTS: Height and weight were recorded from 31170 subjects (16175 male and 14995 female), aged 3-18 y, to construct BMI charts of children and adolescents from central Italy. Percentiles and z-score were calculated using the LMS method of Cole. Serum leptin concentrations were assayed in 1929 subjects (996 male and 933 female) after overnight fasting. RESULTS: BMI percentiles of central Italy were higher than those from standards of other European and USA populations. When plotted against the z-score of BMI, serum leptin values were distributed according to an exponential curve, showing a steep pattern and a wide distribution, as BMI values increased. The hypothesis of the existence of two subgroups, based on a different relation between leptin and BMI, was verified and a separation point between the two subgroups was identified using cluster analysis, discriminant analysis and a novel method developed by our group, hereafter referred to as 'regression clustering'. This method allows identification of the value of the independent variable (z-score of BMI) which can be taken as a separation point. This analysis provided the best results and indicated the following separation points: central Italy standard, z-score = 0.72 (76.4th percentile) for males and z-score = 0.69 (75.5th percentile) for females; French standard (the one suggested for a European population by the European Childhood Obesity Group, ECOG), z-score = 1.46 (92.8th percentile) for males and z-score = 1.96 (97.5th percentile) for females. Similar but variable results were obtained when the same analysis was performed on serum leptin concentration, subdivided according to pubertal development (stage I, stage II-III, stage IV-V). CONCLUSIONS: Children and adolescents from central Italy had greater BMI percentiles when compared to other European populations. Fasting serum leptin concentrations showed a distribution pattern related to z-score, thus allowing to identification of two different subgroups. The z-scores of BMI, identified as separation points, indicated a trend to leptin production by adipocytes that could be taken as indicators of significant increases of fat mass. This study proposes criteria and a statistical approach that could be useful in the identification of BMI cut-off values when screening children and adolescents for overweight.

Blood glucose, plasma insulin and glucagon response to arginine in infants during the first month of life.

Blood glucose, plasma insulin and plasma glucagon were determined during an arginine test at 0, 30 and 60 min in 1 to 7 and 30 day infants. The results were compared with those obtained in the 2-10-year-old children. Basal levels of blood glucose increased from the 1st to the 30th day; by the 30th day they were comparable with those observed in the 2-10-year-old children. Basal levels of plasma insulin were higher in 1 day infants, lower in 7 day infants and similar to those of the 2-10-year-old children in the 30 day infants. Basal values of plasma glucagon were higher in 1 day infants than in the 2-10-year-old children; the lowest levels were found in 7 day infants. After arginine, blood glucose increased in the 2-10-year-old children, the variations were negligible in the 1 to 7 and 30 day infants. Plasma insulin increased in 2-10-year-old children, there was a slight increase in 1 and 30 day infants and a negligible one in the 7 day infants. Plasma glucagon increased in the 2-10-year old children, and was similar in 1 day infants; the increase was reduced in 30 day infants and virtually absent in 7 day infants. These results suggest that there is a transitory alpha cell insensitivity to arginine during the first week of life.

The capnogram in the study of chronic obstructive lung disease.

The purpose of this study is: 1) to emphasize the importance of the capnogram in the investigation of ventilatory disorders of the obstructive type; 2) to propose a numerical parameter representative of the capnogram; 3) to ascertain, by means of this parameter, possible correlations between capnogram changes and other tests of lung function. This parameter enables a quantitative criterion to be substituted for a descriptive one in assessment of the capnogram; The study covered 245 patients with chronic obstructive lung disease; We observed that as the capnographic tracing becomes more and more pathological, the lung function tests show progressive deterioration.