Table 2.

Adjusted variables in studies included in the meta-analysis.

Author (year)	Variables of adjustment
Klein (2008)	Age, gender, race/ethnicity, and study site.
Karesvuo (2013)	Age, smoking, diabetes, carriage of salivary pathogens, and hypertension.
Wagley (2015)	Age, gender, race/ethnicity, education, poverty income ratio, smoking, hypertension, BMI, CRP, and CVD.
Shin (2017)	Age, gender, education, house income, smoking, hypertension, CVD, anemia, hepatitis B infection, serum HDL level, BMI, serum ferritin level, and white blood cell count.
Sun (2019)	Age, gender, hypertension, diabetes, hyperlipidemia, asthma/COPD, CLD, and CKD.

Abbreviations: BMI: Body Mass Index; CRP: C-reactive protein; CVD: cardiovascular disease; HDL: high-density lipoprotein; COPD: chronic obstructive pulmonary disease; CLD: chronic liver disease and cirrhosis; CKD: chronic kidney disease.