The SG90 cohort of the oldest-old in Singapore

The world population is ageing fast and the number of oldest-old has been increasing in the past decades. In 2020, more than 147 million people globally were between the ages of 80–99 years, accounting for 1.9% of the global population, and one in a thousand persons live to 100 years old or older [1]. A nation or region is considered “ageing,” “aged,” or “super-aged” when the percentage of individuals aged 65 and above exceeds 7%, 14%, and 20%, respectively. Singapore is one of the countries with the fastest population ageing [2]. Singapore surpassed the 14% mark in 2021, officially categorizing it as an “aged” nation, and is expected to reach the “super-aged” category by 2030 with one in four Singaporeans aged 65 years and over [3]. The percentage of oldest old individuals who are aged 85 years and older among the population of 65 years older in Singapore is projected to increase from 9.2% in 2020 to 26.8% in 2060 [4].

While our life expectancy is increasing, our likelihood of living without chronic diseases or disabilities of ageing, termed healthspan, has not increased to the same extent [5]. The gap between lifespan and healthspan is increasing and estimated to be around 9 years [6]. A greater number of years with diseases and disabilities is not only associated with a higher healthcare cost [7], but also a lower quality of life [8]. This is especially relevant to Singapore as the current gap in Singapore averages is around 11 years, which is greater than the global average [9]. Ageing processes are predominantly studied in animal models and findings cannot be directly translated to humans without clinical studies [10]. Therewith, epidemiological studies representing a myriad of factors involved in healthy longevity are needed. Cohort studies enable the collection of comprehensive data, offering preliminary insights into potential intervention targets that can subsequently be tested in interventional studies to establish causal relationships [11]. There are several oldest-old cohort studies including Western populations, such as the Leiden 85-plus cohort [12], the Newcastle 85 + study [13], and the 90 + study from US [14]. In Eastern populations, the Chinese Longitudinal Healthy Longevity Survey (CLHLS) [15] and China Health and Retirement Longitudinal Study (CHARLS) [16] have explored the health profile of the Han Chinese; the Sukagawa Study focuses on Japanese aged 75 years above [17]. However, it should be highlighted that knowledge on the biological and clinical ageing phenotypes and their determinants among the oldest-old is still limited. Asian populations represent the majority of oldest old in the world, whereas the majority of previous findings are based on Western populations. Asians are different from their Western counterparts in terms of genetics, lifestyle, culture and other determinants [18‐20]. The SG90 cohort study attempts to fill some of the important gaps in knowledge by following a cohort of oldest-old Singaporeans.

The primary objective of the SG90 cohort study is to characterize healthy ageing in the oldest-old, identifying a range of modifiable medical, biological, lifestyle, psychological, behavioural, and social factors that may contribute to healthy longevity, thus creating a comprehensive foundation for guiding future intervention studies.

The total included 1,158 participants had a median age of 87 years old [interquartile range (IQR): 86–89)] and 64.5% of female. Most participants were of Chinese ethnicity (97.5%) with Taoism or Buddhism belief. No formal education was received in 46.9% of participants with a higher frequency in female. Most participants were widowed (64.1%), with a higher proportion of females than males. Nearly half (47.0%) lived in 4–5 room Housing and Development Board (HDB) flats, and 12.4% lived alone. Most participants were non-smokers (72.1%), never or rarely consumed alcohol (94.9%) and reported often exercising 2–3 times per week (66.5%) (Table 2). Participants tended to be functional independent with a median Barthel Index basic activities of daily living score of 20 (IQR: 19–20) and Lawton and Brody instrumental activities of daily living score of 14 (IQR: 11–16). The quality of life score was relatively higher in males than females with a mean score of 73.3 [standard deviation (SD): 9.5] and 70.8 (SD: 10.5), respectively. 36% of participants rated their self-reported health as good to excellent, while 25.4% of participants reported their health as poor. One quarter of participants experienced falls in the past one year (24.2%) and reported having arthritis (24.6%) and/or diabetes (24.1%). Hypertension was the most common medical condition (76.7%), followed by high cholesterol (66.0%), with a median sitting systolic blood pressure of 139.8 mmHg (SD: 20.2). Men had a median height of 161 cm (IQR: 157–165), mean weight of 58.0 kg (SD: 10.2), and median body mass index (BMI) of 22.4 kg/m² (IQR: 19.7–24.6), indicating that most male participants were within the normal-weight range. Women had a median height of 148 cm (IQR: 144–152), mean weight of 51.8 kg (SD: 10.0), and median BMI of 23.4 kg/m² (IQR: 20.7–26.4), suggesting on average female participants fell within the overweight category according to Asian BMI thresholds. The mean waist circumference was 87.9 cm (SD: 10.4) in men and 87.0 cm (SD: 11.1) in women, indicating that on average men were slightly below, while women exceeded, the Asian abdominal obesity cut-off which is ≥ 90 cm for men, ≥ 80 cm for women. Men showed better physical performance with a higher median handgrip strength (22.2 kg, IQR: 18.4–26.0) and a higher median SPPB score (7, IQR: 5–9) compared to women who had a median handgrip strength of 13.5 kg (IQR: 10.5–16.2) and a median SPPB score of 4 (IQR: 2–6), reflecting expected sex differences in muscle strength and functional capacity among older adults. Participants had a median MMSE score of 23 (IQR: 19–26) and a median GDS-15 score of 3 (IQR: 1–6) indicating mild to moderate cognitive impairment and minimal depressive symptoms (Table 3). The above provides an overview of the descriptive statistics of the SG90 cohort. More findings on specific research questions have been detailed elsewhere [22, 34‐37].

The SG90 cohort focuses on an understudied population, the oldest-old in Southeast Asia, which allows for investigation on the determinants of healthy ageing and development of potential interventions to promote longevity and quality of life. The detailed questionnaire and tests applied cover a broad spectrum of physical, mental and social health-related factors, and provide a comprehensive view of this population’s well-being. Additional extensive biomaterial sampling enables a variety of biological assessments, presenting the participants’ biological profiles but also serving as a valuable biobank for future investigations into ageing processes. Nevertheless, there are some limitations. The cohort may be prone to healthier volunteer bias, as those able to participate and provide biospecimens could be in better health than the general oldest-old population. The recall bias could not be ruled out, particularly from self-reported data on health history and behaviours which might affect the accuracy of some data points. Generalizability may be limited due to the dominance of Chinese participants, with fewer Malay and Indian individuals represented.