Relationship between fat mass and bone: associations between vitamin D, osteocalcin, adipokines and glucose homeostasis among children and adolescents

Author(s)

Kelly Virecoulon Giudici

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Faculdade de Saúde Pública (FSP/CIR)
• Defense date: 2015-10-05

Examining board members

Ligia Araujo Martini; Ana Raimunda Dâmaso; Regina Mara Fisberg; Marcelo Macedo Rogero; Bruno Ferraz de Souza

• Advisor: Ligia Araujo Martini

Abstract

Introduction: Bone and adipose tissue interact and influence glucose homeostasis through the action of their products (leptin, adiponectin and osteocalcin). Vitamin D insufficiency can lead to metabolic alterations in both tissues. Objectives: To investigate the relationships between serum 25 hidroxivitamin D [25(OH)D], osteocalcin, adipokines, markers of glucose metabolism and nutritional status among children and adolescents. Methods: Cross-sectional study with 198 Brazilian (14 to 18 years old) and 318 American (8 to 13 years old) individuals. Blood was collected after 12-hour fasting to measure 25(OH)D, parathyroid hormone (PTH), carboxylated osteocalcin (cOC), adiponectin (A), total cholesterol, triglycerides, HDL-c, LDL-c and VLDL-c (Brazilian sample); total osteocalcin (tOC) (American sample); glucose, insulin, undercarboxylated osteocalcin (ucOC) and leptin (L) (both samples). Markers of glucose metabolism were calculated (HOMA-IR, HOMA- and QUICKI). Among Brazilian individuals, physical activity level was determined and food intake was assessed by a 24-hour food record, repeated in 62.6 per cent of the sample. Results: Brazilian population Individuals with weight excess (42.6 per cent from the total) presented lower serum 25(OH)D, adiponectin, cOC, ucOC, HDL-c and QUICKI, and higher PTH, leptin, LDL-c, VLDL-c, total cholesterol, triglycerides, insulin, HOMA-IR and HOMA-, compared to normal weight individuals (p<0.05). Serum 25(OH)D positively correlated with ucOC (r=0.326; p<0.0001), adiponectin (r=0.151; p=0.034) and HDL-c (r=0.323; p<0.0001), and negatively correlated with BMI (r = -0.294; p<0.0001). The association between 25(OH)D and ucOC persisted after adjusting for age, BMI and season of the year (partial R² = 0.071, p<0.0001), but none of them were related to markers of glucose metabolism. Strong correlations were observed between leptin and insulin (r = 0.746; p<0.0001), HOMA-IR (r = 0.720; p<0.0001), HOMA- (r = 0.703; p<0.0001) and QUICKI (r = -0.749; p<0.0001). A/L ratio was lower among sedentary/insufficiently active subjects (2.2, SD=4.0 vs 5.6, SD=12.3; p=0.01), compared to active/very active subjects. Serum 25(OH)D positively associated with vitamin D intake, after adjusting for sex, sun exposure and season of the year in regression analysis (partial R2=0.026; p=0.02). American population Compared to normal weight individuals, those with weight 17 excess (43.1 per cent ) presented higher leptin, insulin, HOMA-IR and HOMA-, and lower QUICKI (p<0.0001 for all). Serum ucOC negatively correlated with leptin (r = -0.162; p=0.04) and glucose (r = -0.159; p=0.04), but only the association with leptin persisted after adjusting for age, sex and body fat mass percentage (partial R² = 0.03; p=0.0275). Leptin concentrations were related with all markers of glucose metabolism, even after adjusting for age, sex and fat mass (insulin: partial R² = 0.23; glucose: partial R² = 0.04; HOMA-IR: partial R² = 0.23; HOMA-: partial R² = 0.09; partial QUICKI: R² = 0.23, p<0.001 for all). Conclusions: Results confirm the relationship between weight excess, leptin and markers of glucose metabolism among Brazilian and American children and adolescents. Serum 25(OH)D negatively correlated with BMI and leptin and positively correlated with ucOC. However, the relationship between osteocalcin and glucose homeostasis was not directly observed. Findings reinforce the importance if fighting obesity, especially during childhood and adolescence, ages in which important physiological alterations and body changes occur. (AU)

• FAPESP's process: 11/22768-2 - Relationship between fat mass and bone: metabolic interaction between vitamin D, vitamin D receptor genotype, osteocalcin and leptin in adolescentes
• Grantee: Kelly Virecoulon Giudici
• Support Opportunities: Scholarships in Brazil - Doctorate (Direct)