Life Expectancy in Diabetes: What does the Data Reveal?CHAPTER 1

Healthy life expectancy (HLE) is measured as the average number of years expected to be lived in full health by incorporating the number of years to be lived with disability. Life expectancy (LE) indicates mortality in a population, whereas HLE is an indicator of both morbidity and mortality.¹ India is experiencing an incline in morbidity and decline in HLE as chronic diseases such as diabetes are becoming increasingly prevalent at a younger age resulting in a larger proportion of life spent in disability.¹ Hence, the management strategies should aim at extending HLE and not merely life expectancy. This review will reflect on the burden of diabetes and its effect on longevity while highlighting the risk factors and the measures to increase the life expectancy in diabetics.

Many researchers have hypothesized that diabetes will rise to epidemic proportions by 2025. It has been estimated that the highest number of diabetics live in China, India, and the United States of America.² The United States (US) has witnessed a four-fold increase in the prevalence of diabetes over the past 50 years with a particularly steep incline in the last decade. It is predicted that by 2050 the diagnosed cases of diabetes mellitus in the US would have climbed to 39 million.³ In 2008, India's share of the global diabetes burden was estimated to be 15% with 35 million people suffering from this disease. Furthermore, analyses predicted the number of diabetics in India to hit the 70 million mark by 2025 (Fig. 1).¹

The longer life expectancy in diabetics is associated with an earlier onset of the disease and a decline in the mortality rate associated with it. It leads to a larger proportion of life lived with diabetes and associated risk of complications.⁴ Bélanger et al. calculated that 59.9% of the women lead only 33% of their life free from disability. On the other hand, 67.5% of the total population of men spend 41% of their life with a disability. Moreover, diabetes was found to have the greatest impact on the decline of HLE than any other disorder.²

It leads to a lack of knowledge and understanding of life expectancy for patients with T1DM.⁵

Alteration in life expectancy with T2DM was analyzed with over 10 years of data from Germany. At the age of 50 years, men were expected to spend 5.4 years of their remaining total life expectancy with T2DM in 2005 which increased to 7.6 years in 2014. Women at the age of 50 years had a life expectancy with T2DM of 6.3 years in 2005 and 8.3 years in 2014. It concluded that life expectancy with T2DM has shown a consistent increase over the observation period.⁶ A similar conclusion was drawn by prospective analysis of the impact of diabetes on life expectancy in the US by investigating 12 years of data. At the age of 30 years, diabetes was found responsible for a reduction of 0.83 years of life expectancy for US men and 0.89 years for US women.⁷ Another cohort study conducted in England investigated life expectancy and cause-specific mortality rates associated with T2DM using research data of 18 years. Researchers found that at the age of 40 years, white men and women with diabetes lost 5 and 6 years of their life respectively as compared with those without diabetes. A loss of 1 and 2 years respectively was observed for South Asians and blacks with diabetes in the same study.⁸ A similar retrospective study compared mortality rates and decline in life expectancy of Iranian patients with T2DM with the general population. Analysis of 18 years of follow-up data revealed that men and women living with diabetes lost an average of 13.2 and 13.9 years of life, respectively. The estimated loss of life expectancy was greater in younger patients and a gradual decline was observed with the increasing age at the time of diagnosis of diabetes.⁹

Currently, the overall life expectancy in India is below 70 years. T2DM is known to reduce life expectancy by 6–8 years. As life expectancy increases, the prevalence of T2DM also could be expected to increase as age is a nonmodifiable risk factors for T2DM.¹¹ An epidemiological study conducted in the urban population of south India found that mortality rate in diabetic patients is double of that seen in nondiabetics. Cardiovascular disease (CVD) is the greatest contributor to fatal outcomes among diabetic subjects with 24% of CVD mortality seen in patients below 50 years of age. It further affirms the previous reports of premature deaths secondary to CVD in India.¹² In a similar study with north Indian population, mean age at death for people with diabetes was found to be 60.07 years in men and 57.36 years in women.¹³ Data revealed significantly lower life expectancy in diabetics.

Long-term complications of diabetes can impair the entire body through various pathological mechanisms.² The main risk factors for decline in life expectancy in T2DM include various patient factors and pathological processes as listed in Table 1.⁴

Patients with T2DM have a high rate of CVD, myocardial infarction, and stroke with CVD being the leading cause of premature mortality.^3,4 Prevalence of CVD in diabetics is two to four times of its prevalence in nondiabetics. It further contributes to the added healthcare cost, decreased quality of life, and decline in life expectancy of diabetics.⁴ India ranks first in the number of people with diabetes and it is also a forecast to have the highest number of deaths owing to CVD in the next 15 years.¹² Therefore, the management strategy for diabetics is aimed at reducing the absolute risk of CVD down to the level of a similar person without diabetes.

The absolute risk depends on various factors such as age, duration of diabetes, known risk factors, comorbidities, complications, and genetic variation.⁴ Epidemiologic analyses suggest that the risk for CVD in diabetics is directly proportional to the increases in glycated hemoglobin (HbA1c), blood pressure, low-density lipoprotein (LDL), and triglycerides and inversely proportional with the increase in high-density lipoprotein (HDL).³ Several studies examining cause-specific mortality and/or morbidity rates, and their effects on active life expectancy found that curbing CVDs had the greatest impact on increasing life expectancy. Also, Bélanger et al. reported that among all diseases, diabetes posed the greatest threat to a healthy lifespan and led to a great reduction in the life expectancy. Researchers suggested that the associations between diabetes and cardiac disorders could be held responsible for this effect.²

The primary mechanism of diabetes prevention includes weight loss and exercise which provides numerous adjuvant benefits such as drop in the rate of hypertension, heart disease, stroke, and dementia.² A worldwide analysis of the burden of disease and life expectancy estimated that physical inactivity causes 6–10% of the major noncommunicable diseases of coronary heart disease, T2DM, breast cancer and colon cancer.¹⁴ Exercise interventions for patients with diabetes are beneficial in maintaining the homeostasis of glucose and reducing the mortality rate from any cause and diabetes in particular.¹⁵

Patients’ adherence to therapies intended to control risk factors such as dyslipidemia or hypertension in patients with T2DM reduces major cardiovascular complications and leads to an increase in life expectancy.¹⁷ Modifiable risk factors for diabetes include obesity, qualitative aspects of diet, and physical activity.¹⁸ Risk communication with the patient through posters, leaflets, or verbal guidance increases patients’ awareness, understanding, and comprehension of the disease and its complications. The knowledge of the potential benefits of improving modifiable risk factors may also increase patients’ acceptance toward management strategies recommended by their doctor. J Leal et al. developed life-expectancy tables for people with T2DM which confirmed that there is substantial scope for increasing a patient's life expectancy by improving modifiable risk factors.¹⁷ However, clinical practice recommendations by RSSDI-ESI states that special consideration is required before prescribing lipid-lowering agents to elderly (>85 years of age) patients with diabetes mellitus as the expected increase in life expectancy can be overshadowed by the adverse effects of the drug.¹⁹ The United States Food and Drug Administration (US-FDA) also states that the data supporting the application of cholesterol-lowering agents such as fibrates for CVD protection is insufficient and more evidence-based trials are needed.¹⁹

Several researchers have demonstrated the decline in HLE secondary to diabetes. The American Heart Association is striving to increase the global HLE from the age of 64 years to at least 67 years and in the United States from the age of 66 years to at least 68 years by 2030. The key committee stated that the health-adjusted life expectancy can be increased by improving health, preventing or prolonging the onset of disease, minimizing the severity of disease, and increasing the life expectancy (Fig. 2).²⁰4