Diabetes mellitus (DM) confers an increased risk of mortality in young and middle-aged individuals and in women. It is uncertain, however, whether excess DM mortality continues beyond age 75 years, is related to type of hypoglycemic therapy, and whether women continue to be disproportionately affected by DM into older age.
Methods and Findings
From the Cardiovascular Health Study, a prospective study of 5,888 adults, we examined 5,372 participants aged 65 y or above without DM (91.2%), 322 with DM treated with oral hypoglycemic agents (OHGAs) (5.5%), and 194 with DM treated with insulin (3.3%). Participants were followed (1989–2001) for total, cardiovascular disease (CVD), coronary heart disease (CHD), and non-CVD/noncancer mortality. Compared with non-DM participants, those treated with OHGAs or insulin had adjusted hazard ratios (HRs) for total mortality of 1.33 (95% confidence interval [CI], 1.10 to 1.62) and 2.04 (95% CI, 1.62 to 2.57); CVD mortality, 1.99 (95% CI, 1.54 to 2.57) and 2.16 (95% CI, 1.54 to 3.03); CHD mortality, 2.47 (95% CI, 1.89 to 3.24) and 2.75 (95% CI, 1.95 to 3.87); and infectious and renal mortality, 1.35 (95% CI, 0.70 to 2.59) and 6.55 (95% CI, 4.18 to 10.26), respectively. The interaction of age (65–74 y versus ≥75 y) with DM was not significant. Women treated with OHGAs had a similar HR for total mortality to men, but a higher HR when treated with insulin.
DM mortality risk remains high among older adults in the current era of medical care. Mortality risk and type of mortality differ between OHGA and insulin treatment. Women treated with insulin therapy have an especially high mortality risk. Given the high absolute CVD mortality in older people, those with DM warrant aggressive CVD risk factor reduction.
The negative impact on mortality of diabetes persists into old age. Elderly people with diabetes might be twice as likely to die from CVD as people without diabetes. More aggressive treatment of CVD risk factors in older patients should be considered.
Diabetes is a growing global health problem. By 2030, 300 million people worldwide may have this chronic, incurable disorder, double the current number. People with diabetes have dangerously high amounts of sugar in their blood. Blood-sugar levels are normally controlled by insulin, a hormone made by the pancreas that tells cells to absorb sugar from the blood. This control fails in people with diabetes, either because they make no insulin (type 1 diabetes) or because their cells are insensitive to insulin (type 2 diabetes). Type 1 diabetes is controlled with insulin injections; type 2 diabetes is controlled with diet, exercise, and pills that reduce blood-sugar levels. Long-term complications of diabetes include kidney failure, blindness, and nerve damage. Individuals with diabetes also have an increased risk of developing cardiovascular disease (CVD)—heart problems, strokes, and poor circulation—because of damage to their blood vessels.
Why Was This Study Done?
Epidemiological studies (investigations of disease patterns, causes, and control in populations) have indicated that diabetes increases the risk of death (mortality) from CVD in young and middle-aged people, but it is not known whether this is also true for old people. It is also not known what effect long-term treatment for diabetes has on mortality or whether the risk of death from CVD is decreasing in diabetic people as it is in the general US population. This information would help physicians provide health care and lifestyle advice to people with diabetes. In this study, the researchers have investigated mortality patterns in elderly diabetic people by looking at data collected between 1989 and 2001 by the US Cardiovascular Health Study, an observational study of nearly 6,000 people aged over 65 years (in this type of study participants are observed without imposing any specific changes to their lifestyle, behavior, medical care, or treatments).
What Did the Researchers Do and Find?
Participants were screened at the start of the Cardiovascular Health Study for CVD and diabetes (defined as drug-treated disease), for established CVD risk factors such as high blood pressure and smoking, for recently recognized CVD risk factors (for example, subclinical CVD), and for psychosocial factors associated with diabetes that might influence mortality, such as frailty and depression. At this time, about 5% of the participants were taking oral hypoglycemic agents for diabetes and about 3% were taking insulin. During the 11-year study, 40% of the participants died. After adjusting for CVD risk factors and psychosocial factors, the researchers calculated that people treated with oral hypoglycemic agents were 1.3 times as likely to die from all causes and people treated with insulin were twice as likely to die as people without diabetes. The risk of death from CVD was about twice as high in both groups of diabetic participants as in non-diabetic participants; the risk of death from coronary heart disease was increased about 2.5-fold. These adjusted relative risks are very similar to those found in previous studies. The researchers also report that participants treated with insulin were six times more likely to die from infectious diseases or renal failure than nondiabetic participants, and women treated with insulin had a particularly high mortality risk.
What Do These Findings Mean?
These findings indicate that the negative impact on mortality of diabetes persists into old age and that death from CVD is currently declining in both older diabetic people and nondiabetic people. In addition, they show that diabetic people treated with insulin are at a greater risk of dying relative to people without diabetes and those taking oral hypoglycemic agents. This might reflect the type of diabetes that these people had, but this was not investigated. How long participants had had diabetes was also not considered, nor how many people developed diabetes during the study. These and other limitations might mean that the reported excess mortality due to diabetes is an underestimate. Nevertheless, the estimate that elderly people with diabetes are twice as likely to die from CVD as people without diabetes is important. Many elderly people die anyway because of CVD, so this increased risk represents many more deaths than the similar increased risk in younger diabetic populations. Yet, elderly people often receive less-intensive management of CVD risk factors than younger people. The results of this study suggest that rectifying this situation could prolong the lives of many elderly people with diabetes.
Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.0030400.
MedlinePlus encyclopedia has pages on diabetes, heart disease, stroke and poor circulation
The US National Institute of Diabetes and Digestive and Kidney Diseases provides patient information on diabetes
Information for patients on prevention, diagnosis, and management of diabetes is available from the America Diabetes Association
Patient information is available from the American Heart Association on all aspects of heart disease, including its association with diabetes
Wikipedia pages on diabetes and cardiovascular disease (note that Wikipedia is a free online encyclopedia that anyone can edit)
Further information is available about the Cardiovascular Health Study