Table 2.

Characteristics of included studies.

Study	Country	Design	Subjects	Baseline age	Definition	Inclusion criteria	Exclusion criteria	Follow up	Assessment	Outcome
Rusanen M, et al (2013)	Finland	Cohort Retrospective	Cognitive impairment = 289Control = 1222	Cognitive impairment = 51.5 ± 5.9Control = 50.0 ± 6.0	Cognitive impairment group is the combination of patient with MCI and patient with dementiaThe diagnoses of MCI and dementia were made in the meetings of a review board. The diagnosis of dementia was based on DSM-IV criteria and MCI onMayo Clinic AD Research Center (MCADRC) criteria	Population from four independent, randomly selected, population-based samples originally studied within the framework of the North Karelia Project and the FINMONICA study in 1972, 1977, 1982 or 1987 (midlife visit).	N/A	25 years	DSM IV and Mayo Clinic AD Research Center (MCADRC) criteria	HR for Cognitive Impairment∗: 1.85 (1.05 – 3.28)
Singh B, et al (2014)	United States	Cohort Prospective	MCI = 370Normal cognition = 1055	MCI = 82.8 (77.42 – 85.16)Normal cognition = 78.33 (74.37 – 82.73)	A domain-specific (memory, language, executive function and visuospatial skills)score less than 1.0 standard deviation (SD) below the age-specific mean among the generalpopulation was considered as possible cognitive impairment.A diagnosis of normalcognition, MCI, or dementia was made according to published criteria and was based on aconsensus agreement between the interviewing nurse, examining physician, and theneuropsychologist taking into account all the information collected	Residency in Olmsted County, absence of dementia (determined through medical record review by a behavioral neurologist), and not terminally ill or in hospice. Cognitively normal subjects at baseline.	Prevalent cases of MCI, and individuals who died or dropped out prior to any follow-up	5.1 years	Nurse interview, neurological examination, and neuropsychological testing.	HR for MCI, > 5 years†: 1.58 (1.04-2.40)HR for MCI, ≤ 5 years†: 1.11 (0.70–1.74)
Liao WC, et al (2015)	Taiwan	Cohort Retrospective	COPD +  = 20492COPD - = 40765	COPD +  = 68.2 ± 12.4COPD - = 67.0 ± 12.5	Not reported	COPD and non-COPD patients newly diagnosed between 1998 and 2008 from Taiwan National Health Insurance Research Database (NHIRD)	Patients with a history of dementiaor who were younger than 20 years, loss to follow-up, death or withdrawal from the database, orthe end of 2010	12 years	International Classification of Diseases, Ninth Revision, Clinical Modification	HR for COPD vs non-COPD group for dementia‡:1.27 (1.20–1.36)P < .001
Cherbuin N, et al (2018)	Cuba, Dominican Republic, Peru, Venezuela, Mexico, China, Puerto Rico	Cohort Retrospective	COPD +  = 11098	COPD +  = 74 (65–80 + )	Not reported	COPD patients age 65 years and over	Not reported	3 years	Cognitive tests battery, clinical interviews, and informant reports (including Community Screening Instrument for Dementia; the CERAD wordlist learning and animal naming tests; the GeriatricMental State Examination, and the History and Aetiology Schedule – Dementia Diagnosis and Subtype), and was validated against local clinicians DSM-IVDiagnoses	HR for COPD for dementia§:0.74 (0.43–1.04)P > .05
Xie and Xie (2019)	China	Cohort Prospective	COPD +  = 515COPD - = 4220	Male = 82.21 ± 9.33Female = 83.74 ± 10.13	MCI was defined as positive if the MMSE score was below 17for illiterate participants, below 20 for those with 1–6 years of education, or below 24 for those who had over 6 years of education among Chinese people	Population from Chinese LongitudinalHealth Longevity Survey (CLHLS) 2011/2012 wave	lacked follow-up information,were missing important variable data, or had been diagnosedwith mild cognitive impairment (MCI) or dementia at baseline	3 years	Mini Mental State (MMS) was used to evaluate cognitive status.	HR for MCI, 3 years¶: 1.486 (1.207 – 1.855)

^∗Adjusted for age, sex, education, midlife smoking, APOE, midlife physical activity, systolic blood pressure, body mass index, and total serum cholesterol and late-life vascular diseases.

^†Adjusted for education as a continuous variable, sex where applicable, age at baseline as time variable, Beck Depression Inventory-II, history of stroke, APOEe4 genotype, smoking, diabetes, hypertension, coronary artery disease, z-scores and BMI.

^‡Adjusted for age, sex, urbanization and comorbidities (diabetes, hypertension, stroke, coronary artery disease, depression, head injury).

^§Adjusted for age, sex, education level, smoking, physical activity, hypertension, depression and hazardous alcohol consumption.

^¶Adjusted for baseline prevalence of hypertension, diabetes, stroke, alcohol drinking, current exercise, baseline body mass index, age, gender, marital status, education level.