Table 1. Meta-analyses of neuropeptides.

These meta-analyses were conducted as one sample t-tests using the 16 studies shown in Supplementary Table 1 (significance p = 0.05). In these analyses: For GAL, all 16 were used; Sengupta, Peng Head Neck 2, TCGA, Ye, Cromer and Pyeon Tongue were significant. For BDNF, all 16 were used; Sengupta, Peng Head Neck 2, Ye and Pyeon Floor of Mouth were significant. For NGF, all 16 were used; Peng, Estilo and Talbot were significant. For GDNF, only 12 were used (four of the studies did not look at GDNF levels); Peng Head Neck 2 and TCGA were significant. For NTF3, all 16 were used; TCGA and Peng 2 were significant. For NPY, all 16 were used; TCGA and Peng 2 were significant. For PYY, all 16 were used; Peng Head Neck 2 was significant. For VIP, all 16 were used; Peng Head Neck 2 was significant.

Full Name (Gene)	N (Significant / Non- Significant Studies)	t-test (df)	P
Galanin (GAL)	16 (6/10)	2.6 (15)	0.01005
Brain-derived neurotrophic factor (BDNF)	16 (4/12)	1.789 (15)	0.025
Neural growth factor (NGF)	16 (3/13)	1.364 (15)	0.0963
Glial cell line-derived neurotrophic factor (GDNF)	12 (2/10)	1.0393 (11)	0.1607
Neurotrophin-3 (NTF3)	16 (2/14)	0.8783 (15)	0.1968
Neuropeptide Y (NPY)	16 (2/14)	0.8783 (15)	0.1968
Peptide YY (PYY)	16 (1/15)	0.2 (15)	0.4221
Vasoactive Intestinal Peptide (VIP)	16 (1/15)	0.2 (15)	0.4221