Association between salivary flow rate and depressive symptoms with adjustment for genetic and family environmental factors in Japanese twin study.
OBJECTIVE
The association between salivary flow rate (SFR) and depressive symptoms have been inconclusive. The present study aimed to investigate the association between SFR and depressive symptoms with and without adjustment for genetic and family environmental factors.


METHODS
We conducted a cross-sectional study using twins and measured SFR and depressive symptoms as the outcome and explanatory variables, respectively. We also performed three-step regression analyses by first analysing the association between SFR and depressive symptoms without adjustment for genetic and family environmental factors (individual-level analyses). We then performed between-within analyses using monozygotic (MZ) and same-sex dizygotic (DZ) twin pairs, and finally using only MZ twin pairs. These between-within analyses estimated the coefficients adjusted for genetic and family environmental factors. Furthermore, differences in the associations between individual-level and between-within suggest confounding by genetic and family environmental factors.


RESULTS
We conducted 448 twins aged ≥20 years. In individual-level analyses in males and between-within analyses using MZ and same-sex DZ male twin pairs, SFR associated with depressive symptoms. In between-within analyses using only MZ male twin pairs, SFR did not associate with depressive symptoms. In females, SFR did not associate with depressive symptoms in both individual-level and between-within analyses.


CONCLUSIONS
The present study revealed that the association between SFR and depressive symptoms was affected by common genetic factors in males.


CONCLUSIONS
Understanding this association between SFR and depressive symptoms with adjustment for genetic and family environmental factors could lead to an important consideration for the prevention and treatment of hyposalivation.
Department of Health Promotion Science, Osaka University Graduate School of Medicine, 1-7 Yamadaoka, Suita, Osaka, 565-0871, Japan. haruka.tanaka@mcn.ac.jp.|Mie Prefectural College of Nursing, 1-1-1 Yumegaoka, Tsu, Mie, 514-0116, Japan. haruka.tanaka@mcn.ac.jp.
Haruka
H
Tanaka
Department of Health Promotion Science, Osaka University Graduate School of Medicine, 1-7 Yamadaoka, Suita, Osaka, 565-0871, Japan.|Research Fellow of Japan Society for the Promotion of Science, Tokyo, Japan.
Soshiro
S
Ogata
Department of Prosthodontics, Gerodontology and Oral Rehabilitation, Osaka University Graduate School of Dentistry, 1-8 Yamadaoka, Suita, Osaka, 565-0871, Japan.
Kazunori
K
Ikebe
Department of Prosthodontics, Gerodontology and Oral Rehabilitation, Osaka University Graduate School of Dentistry, 1-8 Yamadaoka, Suita, Osaka, 565-0871, Japan.
Yuko
Y
Kurushima
Department of Prosthodontics, Gerodontology and Oral Rehabilitation, Osaka University Graduate School of Dentistry, 1-8 Yamadaoka, Suita, Osaka, 565-0871, Japan.
Kenichi
K
Matsuda
Department of Prosthodontics, Gerodontology and Oral Rehabilitation, Osaka University Graduate School of Dentistry, 1-8 Yamadaoka, Suita, Osaka, 565-0871, Japan.
Kaori
K
Enoki
Mie Prefectural College of Nursing, 1-1-1 Yumegaoka, Tsu, Mie, 514-0116, Japan.
Kayoko
K
Omura
Center for Twin Research, Osaka University Graduate School of Medicine, 1-7 Yamadaoka, Suita, Osaka, 565-0871, Japan.
Chika
C
Honda
Mie Prefectural College of Nursing, 1-1-1 Yumegaoka, Tsu, Mie, 514-0116, Japan.
Kazuo
K
Hayakawa
D000328:Adult; D015986:Confounding Factors, Epidemiologic; D003430:Cross-Sectional Studies; D003863:Depression / Q000453:epidemiology* / Q000235:genetics*; D004777:Environment; D005260:Female; D006801:Humans; D007564:Japan / Q000453:epidemiology; D008297:Male; D012307:Risk Factors; D012472:Salivation / Q000502:physiology*; D012737:Sex Factors; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic
Depressive symptoms; Hyposalivation; Salivary flow rate; Twin study