The ZARADEMP project (ZARAgoza DEMentia
DEPression project) was designed as a longitudinal,
community-based study to examine the incidence
of dementia and the risk factors in incident cases of
dementia. It was carried out in Zaragoza, a typical,
large city in Spain, with an important proportion
of inhabitants coming from surrounding rural
areas (12). A stratified random sample of individuals
55 years of age and older, with proportional
allocation by age and sex, drawn from the eligible
individuals (n = 157 787) in the Spanish official
census lists of 1991, was invited to participate in
the baseline examination.

The Atherosclerosis Risk in Communities Study (ARIC) is a prospective epidemiologic study conducted in four U.S. communities. ARIC is designed to investigate the etiology and natural history of atherosclerosis, the etiology of clinical atherosclerotic diseases, and variation in cardiovascular risk factors, medical care and disease by race, gender, location, and date. Since 2011 a large ancillary study, the ARIC Neurocognitive Study (ARIC-NCS) has been assessing neurocognitive status and adjudicating possible cases of dementia.

Four ARIC field centers each randomly selected and recruited a cohort sample of approximately 4,000 individuals aged 45-64 from a defined population in their community. A total of 15,792 participants received an extensive baseline examination (visit 1, 1987-1989), including medical, social, and demographic data collection. Subsequent examinations occurred in 1990-92 (visit 2), 1993-95 (visit 3), 1996-98 (visit 4), 2011-2013 (visit 5) and 2016-2017 (visit 6). Visit 7 (2018-2019) is currently in progress. Follow-up occurs annually (semi-annually since 2012) by telephone to maintain contact with participants and to assess health status of the cohort.

The Cardiovascular Health Study (CHS) is an NHLBI-funded observational study of risk factors for cardiovascular disease in adults 65 years or older. Starting in 1989, and continuing through 1999, participants underwent annual extensive clinical examinations. Measurements included traditional risk factors such as blood pressure and lipids as well as measures of subclinical disease, including echocardiography of the heart, carotid ultrasound, and cranial magnetic-resonance imaging (MRI). At six month intervals between clinic visits, and once clinic visits ended, participants were contacted by phone to ascertain hospitalizations and health status.

Information on dementia comes from two Ancillary Studies. The CHS Cognition Study (Dr. Lewis Kuller, PI) included 3608 participants who had an MRI in 1992-94 and who were followed for dementia through 1999. A follow-up study was done at the Pittsburgh field center that included 532 participants followed through 2013 (Dr. Oscar Lopez,PI).

The study is a prospective cohort study that included 400 subjects with MCI enrolled in at Huashan Hospital in Shanghai, China and a followed-up once annually for three years. The objectives are to identify individuals with MCI who convert to AD and to explore factors associated with the conversion. The observation time point is every 12 months and phone interview on 6th, 18th month. The primary endpoint was the time from diagnosis to the conversion from MCI to Probable AD Dementia. The secondary endpoints are the time to conversion from MCI to “Possible AD Dementia” or “Probable AD Dementia”, time to Conversion from MCI to “All-cause Dementia”, Overall survival, Changes in Neuropsychological examinations and Changes in MRI from baseline to the end of follow-up. The planned research duration was from Jan 2012 to Dec 2016.

The Malaysian Cohort study was initiated in 2005 by the Malaysian government. The top-down approach to this population-based cohort study ensured the allocation of sufficient funding for the project which aimed to recruit 100 000 individuals aged 35–70 years. Participants were recruited from rural and urban areas as well as from various socioeconomic groups. The main objectives of the study were to identify risk factors, to study gene-environment interaction and to discover biomarkers for the early detection of cancers and other diseases. At recruitment, a questionnaire-based interview was conducted, biophysical measurements were performed and biospecimens were collected, processed and stored. Baseline investigations included fasting blood sugar, fasting lipid profile, renal profile and full blood count. Active follow-up and reassessment started in 2013 and to date 35,000 participants have been reassessed including biospecimens.

ULSAM is a unique, ongoing, longitudinal, epidemiologic study based on all available men, born between 1920 and 1924, in Uppsala County, Sweden. The men were investigated at the ages of 50, 60, 70, 77, 82 88 and 93 years. The reinvestigations in ULSAM were based on the previous investigations. Full screening and official registry data is available in our databases and more data is continuously added.

Health examination at 93 years of age was carried out between December 2013 and March 2015. To this examination 245 men have been invited. Totally 147 men (60%) participated in the investigation. Of these, 23 men were examined at the hospital and 102 were visited at home by a nurse. In addition, 22 men completed only a questionnaire. To this examination even spouses were invited. In the complete examination 43 spouses have participated and 11 completed only a questionnaire.

The MemoVie cohort study aims to investigate the living conditions or risk factors under which the normal cognitive capacities of the senior population in Luxembourg (? 65?year-old) evolve (1) to mild cognitive impairment (MCI) ? transitory non-clinical stage ? and (2) to AD. Identifying MCI and AD predictors undeniably constitutes a challenge in public health in that it would allow interventions which could protect or delay the occurrence of cognitive disorders in elderly people. In addition, the MemoVie study sets out to generate hitherto unavailable data, and a comprehensive view of the elderly population in the country.

A 1-year follow-up was included in the original design of the study. The enrolled participants have been followed-up.

ASPREE is a double-blind, randomized, placebo-controlled primary prevention trial designed to assess whether daily active treatment of 100 mg enteric-coated aspirin will extend the duration of disability-free life in healthy participants aged 70 years and above except for Hispanic and African American minority groups in the U.S. where the minimum age of entry is 65 years.

The primary objective is to determine whether low-dose aspirin prolongs life, or life free of dementia, or life free of significant, persistent physical disability in the healthy elderly. Secondary objectives relate to the effects of low-dose aspirin on the key outcome areas of death, cardiovascular disease, dementia and cognitive decline, cancer, physical disability, depression and major bleeding episodes. Variables were collected annually through visits and for the purposes of retention telephone calls were scheduled at set points through the 7 years.

The Chinese Longitudinal Healthy Longevity Study (CLHLS) is a large-scale population-based study on health status and quality of life of the elderly in 23 provinces (out of 31 provinces) of China since 1998 with 8 waves so far. The study covers approximately 85% of the total population of China and was conducted to shed light on the determinants of human healthy longevity. The CLHLS tried to interview all consenting centenarians in the sampled counties and cities. For each centenarian interviewee, compatible nearby un-related elderly and younger participants were interviewed, including about one nonagenarian aged 90-99, one octogenarian aged 80-89, 1.5 young-old adult aged 65-79 and 0.7 middle-aged adult aged 40-64. Detailed longitudinal data on physical and mental health, cognitive function, social participation, etc. at old ages were collected from a total of 96,805 face-to-face interviews with 16,557 centenarians, 23,081 nonagenarians, 25,842 octogenarians, 19,650 younger elders aged 65-79, and 11,675 aged 35-64 in the completed 7 waves from 1998 to 2014. For the 26,701 participants who died between these seven waves, data on mortality and quality of life before death (i.e., degree/length of disability and suffering before death) were collected in interviews with a close family member of the deceased. The completed seven waves of CLHLS had collected DNA samples from 24,693 participants, including 4,849 centenarians, 5,190 nonagenarians, 5,274 octogenarians, 4,770 aged 65-79, and 4,609 aged 40-64. The 8th wave of CLHLS is ongoing and expected to be completed by the end of July 2018.

Since 1993 the EAS has used systematic recruiting methods to assemble a cohort of over 2,200 elderly individuals from the Bronx, 26% of whom are African American. The EAS sample is broadly representative of the elderly population in one of the poorest and most racially and ethnically diverse urban counties in the United States.

The EAS has developed, tested, and applied strategies designed to meet the recruitment and retention challenges that may arise when conducting research studies with older adults. In 2004, the EAS began using the Registered Voter Lists (RVL) for Bronx County for continuous recruitment efforts. Individuals of at least 70 years of age, Bronx residents, non-institutionalized and English speaking are randomly selected from updated RVL and sent a letter followed by a screening telephone call. Persons who complete the telephone screening battery and agree to participate in clinical follow-up are invited to enroll. Continuing enrollment has resulted in over 2200 participants by 2017.