Prevalence and correlates of diagnosed and undiagnosed type 2 diabetes mellitus and pre-diabetes in older adults: Findings from the Irish Longitudinal Study on Ageing (TILDA)
Introduction
Diabetes is a leading cause of death and disability globally [1], [2]. The disease is increasingly prevalent, affecting approximately 8.3% of adults worldwide, with this figure projected to increase by 55% over the next two decades [3]. Type 2 diabetes mellitus accounts for over 90% of cases. Major risk factors for type 2 diabetes include increasing age, obesity and physical inactivity [4]. The consequences of the disease are manifold. The development of diabetic retinopathy, nephropathy and neuropathy as well as the increased risk of macrovascular disease may result in reduced physical function, poorer quality of life, an increased number of years lived with disability and early mortality [1], [2], [5]. Consequently, diabetes is estimated to account for over 10% of global healthcare expenditure [6].
Type 2 diabetes can be asymptomatic and therefore remain undiagnosed for several years, with complications often manifest at the time of diagnosis [4]. Undiagnosed diabetes accounts for up to 50% of all cases [7] and has been associated with poorer cardiovascular outcomes [8]. Pre-diabetes, defined as having a blood glucose concentration higher than normal but lower than diabetes thresholds, is also becoming increasingly common. It is estimated that pre-diabetes affects 35% of all adults in the United States, rising to >50% in those aged 65 and over. Up to 70% of individuals with pre-diabetes will go on to develop diabetes at a rate of 5–10% per year [9]. Recent data from the UK indicates that the prevalence of pre-diabetes in adults more than trebled from 11.6% in 2003 to 35.3% in 2011. In those aged 40 and over, the prevalence increased from 17.9% to 48.7% in the same time period [10]. Many of the micro- and macrovascular complications of diabetes may also be present in pre-diabetes [9].
There is limited information available regarding the population prevalence of diagnosed and undiagnosed type 2 diabetes and pre-diabetes in the Republic of Ireland. A 2007 study of 1200 adults aged 45+ estimated a prevalence of diabetes of 8.9% and pre-diabetes of 19.8% [11], [12]; however, these findings need to be confirmed, in a larger sample.
The aim of this study is to document the prevalence of diagnosed, undiagnosed and pre-diabetes in community dwelling adults aged 50 and over in Ireland, and to identify associated demographic, health and lifestyle characteristics.
Section snippets
Sample design
Cross-sectional data from Wave 1 of the Irish Longitudinal Study on Aging (TILDA) was analysed. TILDA is a large, nationally representative prospective study on ageing comprised of community dwelling adults aged 50 and over residing in the Republic of Ireland. The study design is described in detail elsewhere [13]. Briefly, TILDA Wave 1 took place between October 2009 and February 2011. 8175 adults aged 50 and over from 6279 households completed a computer-aided personal interview (CAPI),
Validation of HbA1c analysis in frozen buffy coat samples
Mean (SD) HbA1c was 5.5% (2.7%) (36.2 mmol/mol (6.3 mmol/mol)) measured from fresh whole blood and 5.4% (2.8%) (35.9 mmol/mol (6.8 mmol/mol)) measured from frozen buffy coat. Fig. 1 illustrates the relationship between HbA1c measured from fresh whole blood and frozen buffy coat. A correlation coefficient of r = 0.90 was observed between the methods. Deming regression revealed no significant difference between the two methods (slope = 0.92 (95%CI: 0.80–1.04); mean offset 3.18 mmol/mol (95%CI: −1.08 to
Discussion
This paper outlines the prevalence and correlates of diagnosed, undiagnosed and pre-diabetes in the community-dwelling population aged 50 years and over in Ireland. The total prevalence of type 2 diabetes is 9.5%, with approximately 10% of cases undiagnosed. Diabetes is more prevalent in men than women and increases with advancing age, peaking at 25.2% in men aged 80 years and over. A further 5.5% of the population are estimated to have pre-diabetes.
Compared to other populations, the prevalence
Conflict of interest statement
The authors declare no conflict of interest.
Author contributions
SL contributed to the conception and design of the study, data analysis and interpretation and drafted the manuscript. AMOH contributed to the conception and design of the study and data aquisition, analysis and interpretation. NOL contributed to data analysis and interpretation. MH and MMcC contributed to data acquisition and analysis. JOC and RAK contributed to the conception and design of the study and data analysis and interpretation. All authors critically revised the manuscript and
Acknowledgements
The Irish Longitudinal Study on Ageing is funded by the Irish Government, the Atlantic Philanthropies and Irish Life PLC. This research was additionally supported by the Health Research Board of Ireland (Grant reference: HRA_PHS/2012/30). The sponsors played no role in study design, methods, subject recruitment, data collection, analysis or preparation of paper. We are grateful to all of the TILDA respondents for participating in the study. Researchers interested in using TILDA data may access
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