PREDICTORS OF BONE MINERAL DENSITY IN ADOLESCENTS WITH EXCESS WEIGHT

Adolescence is characterized as a phase of intense development of the skeletal system. Maximizing bone mass acquisition during adolescence may reduce the risk of bone fractures later in life. Objectives: To analyze bone mineral density (BMD) and its relation to nutritional status and serum vitamin D in adolescents with excess weight.

Methods:

This is a cross-sectional, exploratory study. Data from 102 adolescents with excess weight, of both sexes, were analyzed. The following indices were evaluated: body mass index (BMI), abdominal circumference (AC), intake of micronutrients (vitamin D, calcium, magnesium and phosphorus), serum 25-hydroxycholecalciferol (25(OH)D concentration, BMD of the proximal femur, lumbar spine (L1-L4) and total body, % body fat mass (% BFM), total BFM, total body lean mass (BLM), body fat mass (BFMI) and lean mass (BLMI).

Results:

The male adolescents (n=53) had higher values for weight, height, AC, BLM and BLMI, while the females (n=49) had higher % BFM. The majority were obese (53.9%) and had a BMD within the normal range for all evaluation sites. Of the 84 adolescents (n=84) with laboratory examination of 25OHD, 33.3% presented values considered insufficient or deficient. Multivariate linear regression analysis showed that the most important independent predictor of BMD for the girls was BLMI, regardless the evaluation site. For boys, in addition to BLMI, BMI-Z of the proximal femur (neck of the femur and total) was also was a determinant variable for BMD.

Conclusion:

In this sample of adolescents, BLMI was a positive predictor of BMD in both sexes; and BMI-Z was a positive predictor only in proximal femur in the boys. Level of evidence II; Prognostic studies.

Keywords:
Bone density; Obesity; Adolescent; Vitamin D; Body composition

Variable	Total N=102	Female N=49	Male N=53
Age (years)	13 (10-19)	13 (10-17)	14 (10-19)
Age (months)	166.6±27.7	161.7±25.4	171.1±29.2
Weight (kg)^* *()** indicates significant difference between genders;	72.5±17.0	66.3±14.1	78.3±17.5
Height (m)^* *()** indicates significant difference between genders;	1.6±0.1	1.6±0.1	1.7±0.1
Body mass index (kg/m²)	26.7 (20.3-40.6)	26.0 (20.3-35.6)	27.0 (20.3-40.6)
Body mass index (Z-score)	1.6±0.6	1.5±0.5	1.7±0.6
Waist circumference (cm)^* *()** indicates significant difference between genders;	94.6±11.8	91.1±11.6	98.0±11.1
% total fat^* *()** indicates significant difference between genders;	36.5 (13.3-49.3)	39.3 (26.2-45.5)	32.7 (13.3-49.3)
Lean mass (kg)	25.1±9.1	25.2±8.3	25.1±9.9
Fat mass (kg)^* *()** indicates significant difference between genders;	47.4±12.3	41.1±9.2	53.2±12.1
Lean mass index (kg/m²)^* *()** indicates significant difference between genders;	17.7±2.9	16.5±2.8	18.8±2.6
Fat mass index (kg/m²)	9.5±3.3	10.1±2.9	9.0±3.6
Lumbar spine (Z-score)^ () Bone Mineral Density.	0.254±1.169	0.296±1.049	0.215±1.281
Femoral neck (Z-score)^ () Bone Mineral Density.	0.717±1.233	0.769±1.164	0.670±1.301
Total body (Z-score)^ () Bone Mineral Density.	-0.130±1.154	-0.140±1.040	-0.120±1.261
Total femur (Z-score)^ () Bone Mineral Density.	0.338±1.120	0.312±1.111	0.360±1.138
25-Hydroxycholecalciferol (ng/mL)	25.3 (11.5-50.1)	22.8 (13.7-45.7)	25.5 (11.5-50.1)
Calcium (mg)	649.4 (76.8-1771.7)	642.3 (78.6-1771.7)	666.1 (76.8-1443.8)
Phosphorus (mg)	957.2 (115.0-2815.1)	985.4 (115.0-2438.6)	955.3 (212.0-2815.1)
Magnesium (mg)	245.2 (31.7-663.1)	271.1 (31.7-625.6)	231.7 (48.3-663.1)
Vitamin D (mcg)	219.0 (0.4-679.0)	219.1 (0.4-674.1)	221.5 (0.6-679.0)

Variable	Classification	Total % (n)	Female % (n)	Male % (n)
BMI-Z	Eutrophy	7.8 (8)	10.2 (5)	5.7 (3)
	Overweight	38.2 (39)	40.8 (20)	35.9 (19)
	Obesity	53.9 (55)	49.0 (24)	58.5 (31)
	Total	100.0 (102)	100.0 (49)	100.0 (53)
Lumbar spine BMD	Very low	3.0 (3)	2.0 (1)	3.8 (2)
	Low	10.9 (11)	8.2 (4)	13.5 (7)
	Normal	78.2 (79)	83.7 (41)	73.1 (38)
	High	7.9 (8)	6.1 (3)	9.6 (5)
	Total	100.0 (101)	100.0 (49)	100.0 (52)
Total body BMD	Very low	5.9 (6)	4.1 (2)	7.7 (4)
	Low	14.9 (15)	18.4 (9)	11.5 (6)
	Normal	76.2 (77)	77.5 (38)	75.0 (39)
	High	3.0 (3)	0.00 (0)	5.8 (3)
	Total	100.0 (101)	100.0 (49)	100.0 (52)
Femoral neck BMD	Very low	1.0 (1)	0.0 (0)	1.9 (1)
	Low	5.9 (6)	4.2 (2)	7.5 (4)
	Normal	76.2 (77)	77.1 (37)	75.5 (40)
	High	16.8 (17)	18.7 (9)	15.1 (8)
	Total	100.0 (101)	100.0 (48)	100.0 (53)
Total femur BMD	Very low	3.0 (3)	2.1 (1)	3.8 (2)
	Low	6.9 (7)	10.4 (5)	3.8 (2)
	Normal	85.1 (86)	87.5 (42)	83.0 (44)
	High	5.0 (5)	0.0 (0)	9.4 (5)
	Total	100.0 (101)	100.0 (48)	100.0 (53)
Vitamin D (25OHD)	Sufficient	66.7 (56)	63.4 (26)	69.8 (30)
	Insufficient	21.4 (18)	26.8 (11)	16.3 (7)
	Deficient	11.9 (10)	9.8 (4)	13.9 (6)
	Total	100.0 (84)	100.0 (41)	100.0 (43)

Variable	Lumbar spine BMD		Total body BMD		Femoral neck BMD		BMD total femur
	fem	male	fem	male	fem	male	fem	male
Age (years)	-0.076	-0.105	-0.108	-0.064	-0.020	-0.190	-0.060	-0.196
Age (months)	0.051	0.379^ () p<0.01.	0.162	0.399^ () p<0.01.	0.204	0.389^ () p<0.01.	0.072	0.338^* *()** p<0.05;
Weight (kg)	-0.013	0.214	-0.008	0.229	-0.017	0.124	-0.061	0.101
Height (m)	0.118	0.355^ () p<0.01.	0.198	0.304^ () p<0.01.	0.352^* *()** p<0.05;	0.419^ () p<0.01.	0.181	0.362^ () p<0.01.
Body mass index (kg/m²)^# (#) Spermann's correlation; other variables: Pearson correlation;	0.166	0.365^ () p<0.01.	0.269	0.336^* *()** p<0.05;	0.321^* *()** p<0.05;	0.453^ () p<0.01.	0.198	0.435^ () p<0.01.
Body mass index (Z-score)	-0.072	0.219	0.045	0.164	0.173	0.222	0.046	0.178
Waist circumference (cm)^* *()** p<0.05;	-0.105	-0.042	-0.083	-0.128	0.169	0.048	-0.026	-0.008
% total fat^# (#) Spermann's correlation; other variables: Pearson correlation;	-0.046	0.208	0.046	0.179	0.177	0.257	0.014	0.211
Lean mass (kg)	0.120	0.399^ () p<0.01.	0.207	0.452^ () p<0.01.	0.153	0.351^ () p<0.01.	0.124	0.315^* *()** p<0.05;
Fat mass (kg)	0.187	0.499^ () p<0.01.	0.277	0.551^ () p<0.01.	0.237	0.490^ () p<0.01.	0.275	0.456^ () p<0.01.
Lean mass index (kg/m²)^* *()** p<0.05;	-0.025	0.172	0.051	0.128	0.232	0.242	0.067	0.206
Fat mass index (kg/m²)	-0.188	-0.083	-0.150	0.055	-0.331^* *()** p<0.05;	-0.018	-0.217	-0.028
Lumbar spine (Z-score)^ () p<0.01.	-0.053	-0.010	0.107	0.090	-0.031	0.150	0.000	0.035
Femoral neck (Z-score)^ () p<0.01.	-0.062	-0.018	0.121	0.044	-0.029	0.151	-0.010	0.062
Total body (Z-score)^ () p<0.01.	0.059	-0.023	0.227	0.018	0.117	0.085	0.095	0.008
Total femur (Z-score)^ () p<0.01.	0.059	0.013	0.183	0.034	0.110	-0.164	0.080	-0.149
25(OH)D (ng/mL) #	-0.188	-0.083	-0.150	0.055	-0.331^* *()** p<0.05;	-0.018	-0.217	-0.028
Calcium (mg) #	-0.053	-0.010	0.107	0.090	-0.031	0.150	0.000	0.035
Phosphorus (mg) #	-0.062	-0.018	0.121	0.044	-0.029	0.151	-0.010	0.062
Magnesium (mg) #	0.059	-0.023	0.227	0.018	0.117	0.085	0.095	0.008
Vitamin D (mcg) #	0.059	0.013	0.183	0.034	0.110	-0.164	0.080	-0.149

Gender	BMD	Model	R²	Adjusted R²	p
Female	Lumbar spine	There were no significant variables
	Total body	-1.853 + (0.104 x LMI)	0.077	0.057	0.050
	Femoral neck	-1.708 + (0.093 x LMI)	0.109	0.090	0.022
	Total femur	-2.314 + (0.162 x LMI)	0.076	0.055	0.050
Male	Lumbar spine	-4.621 + (0.259 x LMI)	0.249	0.234	<0.001
	Total body	-5.381 + (0.282 x LMI)	0.304	0.290	<0.001
	Femoral neck	-3.921 + (0.184 x LMI) + (0.677x BMI-Z)	0.317	0.289	0.022
	Total femur	-3.371 + (0.147 x LMI) + (0.584 x BMI-Z)	0.282	0.253	0.028

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[1] Correspondence: Luciane Coutinho de Azevedo, Rua São Paulo, 3250, Itoupava Seca. CEP: 89030-000, Blumenau, SC, Brazil. lu.cda@hotmail.com