Table 3 Factors independently associated with IL-6 serum levels in the multivariate linear regression and in the bootstrapping regression model (N = 527)

Age (years)

Continuous

0.01 (0.003)

0.01; 0.02

<  0.0001

0.01 (0.003)

0.01; 0.02

<  0.0001

Sex

Female

Reference

Reference

Male

0.26 (0.07)

0.12; 0.41

0.0005

0.26 (0.07)

0.12; 0.40

0.0005

Current body mass index (kg/m²)

<  18.5

0.08 (0.16)

−0.23; 0.38

0.63

0.07 (0.14)

−0.21; 0.38

0.63

≥ 18.5 < 30

Reference

Reference

≥ 30

0.27 (0.07)

0.12; 0.41

0.0003

0.27 (0.07)

0.14; 0.40

0.0003

Marital status

Not married

Reference

Reference

Married

- 0.16 (0.07)

−0.29; −0.03

0.02

−0.16 (0.07)

−0.29; − 0.02

0.02

Karnofsky Performance Status (%)

90–100

Reference

Reference

60–80

0.38 (0.11)

0.17; 0.58

0.0004

0.37 (0.12)

0.16; 0.64

0.0004

Charlson Comorbidity Index

0

Reference

Reference

1

0.15 (0.07)

0.01; 0.28

0.03

0.15 (0.08)

0.01; 0.31

0.03

≥ 2

0.23 (0.08)

0.07; 0.40

0.006

0.23 (0.07)

0.10; 0.39

0.006

Glottic cancer

No

Reference

Reference

Yes

−0.28 (0.06)

−0.40; −0.16

<  0.0001

− 0.28 (0.06)

− 0.41; − 0.16

<  0.0001

Tobacco consumption (all tobacco products)

Never

Reference

Reference

Former

0.43 (0.13)

0.17; 0.69

0.001

0.43 (0.11)

0.21; 0.63

0.001

Current

0.51 (0.14)

0.23; 0.79

0.0004

0.51 (0.12)

0.26; 0.74

0.0004