3.1 Characteristics of the study population
The clinical characteristics and biochemical data of the controls and subjects with overweight are summarized in Table 1.
Compared to controls, subjects with overweight had significantly higher BW, BMI, WC, WHR, systolic blood pressure (SBP), diastolic blood pressure (DBP), TC, triglycerides, LDL-C, FPG, 30-minPG, 2-hPG, Fins, 30-minIns, 2-hIns, HbA1c, HOMA-IR, serum creatinine (Scr), lower HDL-C and QUICKI. Serum irisin levels were significantly lower in nondiabetic overweight subjects compared to control (11.46 ± 4.11 v s14.78 ± 7.03µg/mL, p = 0.02).
Table 1. Characteristics of the study population
|
Controls
(n=230)
|
Overweight
(n=294)
|
p
|
Age (years)
|
56.74±8.06
|
57.14±8.86
|
0.08
|
Height (cm)
|
160.19±7.64
|
157.61±7.85
|
0.154
|
Weight (kg)
|
59.21±9.09
|
65.58±9.74
|
<0.0001
|
BMI (kg/m2)
|
23±2.49
|
26.37±2.85
|
<0.0001
|
WC (cm)
|
77.16±6.72
|
87.42±6.35
|
<0.0001
|
WHR
|
0.84±0.06
|
0.89±0.05
|
<0.0001
|
SBP (mmHg)
|
115.8±16.04
|
130.89±17.58
|
<0.0001
|
DBP (mmHg)
|
72.68±9.54
|
76.59±11.53
|
<0.0001
|
TG (mmol/L)
|
1.48±1.21
|
1.95±1.41
|
<0.0001
|
TC (mmol/L)
|
4.59±0.86
|
5.06±0.98
|
<0.0001
|
HDL-C (mmol/L)
|
1.59±0.39
|
1.42±0.3
|
<0.0001
|
LDL-C (mmol/L)
|
2.82±0.69
|
2.83±0.66
|
0.0038
|
FPG (mmol/L)
|
5.16±1.05
|
5.58±1.26
|
0.0004
|
30-min PG (mmol/L)
|
9.19±2.38
|
10.47±2.89
|
<0.0001
|
2-h PG (mmol/L)
|
7.01±2.93
|
9±4.23
|
<0.0001
|
HbA1c (%)
|
5.54±0.55
|
5.59±0.73
|
0.02
|
Fins (mIU/mL)
|
6.25±3.96
|
9.65±5.49
|
<0.0001
|
30-min Ins (mIU/mL)
|
51.06±34.42
|
65.94±44.49
|
<0.0001
|
2-h Ins (mIU/mL)
|
37.32±27.26
|
56.36±36.42
|
<0.0001
|
HOMA-IR
|
1.45±1
|
2.45±1.86
|
<0.0001
|
QUICKI
|
0.31±0.05
|
0.27±0.04
|
<0.0001
|
Scr (umol/L)
|
61.61±16.02
|
69.43±17.22
|
<0.0001
|
Irisin (ug/mL)
|
14.78±7.03
|
11.46±4.11
|
0.02
|
BMI, body mass index; WC, waist circumference; WHR, waist to hip ratio; TG, triglycerides; TC, total cholesterol; SBP, systolic blood pressure; DBP, diastolic blood pressure; HDL-C, high density lipoprotein cholesterol; LDL-C, low density lipoprotein cholesterol; FPG, fasting plasma glucose; PG, plasma glucose; Fins, fasting insulin; Ins, insulin; HOMA-IR, homeostatic model for assessment of insulin resistance; QUICKI, quantitative insulin-sensitivity check index; Scr, serum creatinine.
3.2 Correlation of irisin with anthropometric and biochemical parameters
Pearson’s correlation analysis for serum irisin with metabolic parameters are shown in Table 2. Circulating irisin level was positively correlated with QUICKI (r = 0.178, p = 0.045) and triglycerides (r = 0.149, p = 0.022), but was negatively correlated with WC (r = -0.185, p = 0.037), WHR (r = -0.176, p = 0.047), Fins (r = -0.2, p = 0.024), Scr (r = -0.243, p= 0.006) and HOMA-IR (r = -0.189, p = 0.033). Irisin was not correlated with cholesterol (TC, HDL-C and LDL-C), glucose (fasting glucose, postprandial glucose and HbA1C) and blood pressure (SBP and DBP).
Table 2. Correlation of irisin with anthropometric and metabolic parameters
|
r
|
p
|
Weight
|
-0.09
|
0.313
|
BMI
|
-0.124
|
0.165
|
WC
|
-0.185*
|
0.037
|
WHR
|
-0.176*
|
0.047
|
SBP
|
-0.087
|
0.329
|
DBP
|
0.02
|
0.826
|
TG
|
0.149*
|
0.022
|
TC
|
-0.026
|
0.775
|
HDL-C
|
0.046
|
0.608
|
LDL-C
|
0.03
|
0.736
|
FPG
|
0.023
|
0.799
|
30-min PG
|
-0.11
|
0.215
|
2-h PG
|
-0.115
|
0.196
|
HbA1c
|
0.038
|
0.671
|
Fins
|
-0.2*
|
0.024
|
30-min Ins
|
0.062
|
0.49
|
2-h Ins
|
-0.108
|
0.225
|
HOMA-IR
|
-0.189*
|
0.033
|
QUICKI
|
0.178*
|
0.045
|
Scr
|
-0.243*
|
0.006
|
BMI, body mass index; WC, waist circumference; WHR, waist to hip ratio; TG, triglycerides; TC, total cholesterol; SBP, systolic blood pressure; DBP, diastolic blood pressure; HDL-C, high density lipoprotein cholesterol; LDL-C, low density lipoprotein cholesterol; FPG, fasting plasma glucose; PG, plasma glucose; Fins, fasting insulin; Ins, insulin; HOMA-IR, homeostatic model for assessment of insulin resistance; QUICKI, quantitative insulin-sensitivity check index; Scr, serum creatinine. r, Pearson correlation coefficient. *p < 0.05 is significant.
3.3 Multiple linear regression of irisin with HOMA-IR
Multiple linear regression was performed to assess the association of irisin with HOMA-IR (Table 3). Our results showed that irisin was negative associated with HOMA-IR (β = -0.342, p = 0.029) after adjustment of age, sex, smoking, alcohol and medication use.
Table 3. Multiple linear regression of irisin with HOMA-IR
|
β±SE of β
|
t-Value
|
p
|
Age
|
0.014±0.006
|
2.6
|
0.01
|
Sex
|
0.153±0.113
|
1.35
|
0.181
|
BMI
|
0.063±0.016
|
3.93
|
0.0002
|
Irisin
|
-0.342±0.154
|
-2.22
|
0.029
|
Sex, age smoking, alcohol and medication use were adjusted for model. BMI, body mass index; β, regression coefficient; SE, standard error; p < 0.05 is significant.
3.4 Multivariate logistic regression analysis of irisin with odds of overweight
In order to analyze the association of irisin with odds of overweight, logistic regression was performed. We coded overweight = 1 (BM ≧25kg/m2) and normal controls = 0 (18.5≦BMI < 25 kg/m2) as shown in Table 4. Higher level of irisin was significantly associated with decreased odds of overweight with odds ratio of 0.281 (β = -1.271, 95% CI: 0.093 ~ 0.851, p = 0.024).
Table 4. Logistic regression analysis of irisin with odds of overweight
|
β
|
OR
|
95%CI
|
p
|
Model: Overweight (BMI≧25kg/m2) = 1, Controls = 0
|
Age
|
0.035
|
1.035
|
(0.99~1.083)
|
0.132
|
Sex
|
-1.421
|
0.242
|
(0.106~0.548)
|
0.000
|
Irisin
|
-1.271
|
0.281
|
(0.093~0.851)
|
0.024
|
Age, sex, smoking, alcohol and medication use were adjusted. β, regression coefficient; OR, odds ratio; 95% CI, 95% confidence interval, p < 0.05 is significant.