Insulin-like growth factor-1 is a mediator of age-related decline of bone health status in men

Figures & data

Figure 1. The proposed scheme of mediation.

Table 1. Characteristics of the subjects.

	Chinese (n = 140)	Malay (n =139)	Overall (n = 279)	p Value
	Mean (SD)	Mean (SD)	Mean (SD)
Age (years)	45.48 (15.20)	44.37 (15.33)	44.92 (15.25)	0.546
Weight (kg)	68.59 (13.21)	71.79 (13.42)	70.19 (13.38)	0.046
Height (cm)	168.97 (6.79)	166.57 (6.60)	167.77 (6.79)	0.003
BMI (kg/m^2)	23.95 (3.87)	25.79 (4.36)	24.87 (4.22)	<0.001
SOS (m/s)	1518.89 (28.15)	1520.26 (28.96)	1519.57 (28.52)	0.689
Total testosterone (nmol/l)	18.64 (5.90)	18.46 (6.15)	18.55 (6.02)	0.805
	Median (IQR)	Median (IQR)	Median (IQR)
SHBG (nmol/l)	39.13 (25.27)	35.48 (25.60)	37.27 (26.24)	0.045
IGF-1 (pg/ml)	301.50 (282.47)	272.20 (238.70)	284.30 (270.90)	0.867

The comparison between Chinese and Malay men is made using independent t test. The data of SHBG and IGF-1 is skewed and the log-transformed data is used for analysis. Normal data is presented in mean (standard deviation) while skewed data is presented in median (interquartile range). p Value in bold indicates a significant difference between the two groups.

BMI, body mass index; IGF-1, insulin-like growth factor-1; IQR, interquartile range; SD, standard deviation; SHBG, sex hormone-binding globulin; SOS, calcaneal speed of sound.

Table 2. Correlation analysis among the studied variables.

	Age	BMI	SOS	TT	SHBG	IGF-1
Age	1
BMI	−0.026	1
SOS	−0.318	0.132	1
TT	−0.154	−0.432	0.099	1
SHBG	0.248	−0.356	−0.059	0.575	1
IGF-1	−0.783	−0.085	0.231	0.035	−0.216	1

The numbers in the tables indicate correlation coefficient (r), and those in bold indicate significant correlations (p < 0.05).

BMI, body mass index; IGF-1, insulin-like growth factor-1; TT, total testosterone; SHBG, sex hormone-binding globulin; SOS, calcaneal speed of sound.

Table 3. Multiple regression analysis on the associations among age, insulin-like growth factor-1 and calcaneal speed of sound.

Model	Dependent variable	Independent variable*	Unstandardized regression coefficient	Standard error	Standardized regression coefficient	p Value
1	log IGF-1	Age	−0.014	0.001	−0.796	<0.001
2	SOS	log IGF-1	28.445	6.302	0.269	<0.001
3	SOS	log IGF-1 adjusted for age	6.929	9.36	0.065	0.46
4	SOS	Age	−0.637	0.116	−0.341	<0.001
5	SOS	Age adjusted for IGF-1	−0.54	0.176	−0.289	0.002

The p values in bold indicate significant association. All of the regression models are adjusted for body mass index, log-sex hormone-binding globulin and total testosterone level. For the Sobel test, unstandardized regression coefficients and standard errors for model 1, 2 and 4 are used.

IGF-1, insulin-like growth factor-1; SOS, calcaneal speed of sound.