In this population-based cohort study we observed a decline in mortality rates of older individuals between the two study periods, together with favourable changes in risk factors and an increase in medical treatment. The observed decline in the cardiovascular and all-cause mortality rates in our study are comparable, according to Statistics Iceland , to the decline seen between 1993 and 2004 for the same age group in the Icelandic population at large, of 36% (95% CI 25%-45%) in cardiovascular, and 21% (95% CI 14%-28%) in all-cause mortality rates. As the decline in coronary heart disease mortality over recent decades has been attributed to a reduction in cardiovascular risk factors  we adjusted for mean values of risk factors and medical treatment over the two cohorts and found that the estimated cardiovascular mortality rate fell from 32% to 25%, indicating that the decline in mortality rate is only partly due to a reduction in cardiovascular risk factors and increase in medical treatment, and therefore remains to be fully explained.
The decline in both cardiovascular and all-cause mortality rates observed was somewhat greater in individuals with diabetes than in those without, although the difference did not reach statistical significance. The age- and sex-adjusted hazard ratio for cardiovascular mortality declined from 2.21 in 1993 to 1.69 in 2004, and for all-cause mortality, from 1.66 to 1.47. Compared to the estimated relative risk of death from all causes, between 1967 and 1991, of 1.9 for men and 1.7 for women with type 2 diabetes, in a middle-aged Icelandic cohort , the hazard ratio for death from all causes in the cohort of older individuals from 1993 is only slightly lower. The low number of participants in the 1993 cohort, however, does not allow a detailed study on the effect of either disease duration or the difference between men and women, so the comparison must be made with caution.
The observed attenuation in hazard ratio after adjusting for cardiovascular risk factors did not alter the trend in hazard ratio reduction between the two time points, emphasizing that the increased mortality rate of those with type 2 diabetes persisted over time, and was independent of cardiovascular risk factors. Our results are thus in agreement with those from a collaborative meta-analysis of 102 prospective studies, that conventional cardiovascular risk factors do not explain why twice the incidence of cardiovascular diseases is seen in those with type 2 diabetes than in those without diabetes .
It has been shown that the increased mortality risk for persons with type 2 diabetes is related to both age at onset and duration of disease. In an observational study from Tayside, Scotland, Barnett and co-workers showed that hazard ratios for mortality decreased with increasing age at diagnosis, and increased mortality risk was not evident until 2 years after diagnosis . There was a trend towards increasing risk with increasing duration of disease, which started to decline 8 years after diagnosis. In our study the mean duration of disease was just over 10 years in both cohorts, but the percentage of individuals diagnosed at baseline was much higher in the cohort from 1993, i.e. 59% compared to 41% in 2004, so the mean duration of disease until the end of follow-up was lower in 1993 than in 2004. Increased awareness of the risk of diabetes in old age, both among professionals and the general public, may be the reason for the increase in diagnosed diabetes at entry in the AGES-Reykjavik cohort, and those in the Reykjavik Study cohort may, therefore, have had untreated disease for some time. The possible over diagnosis using only one glucose measurement  for newly diagnosed diabetes, may have led to both a greater dilution bias and a shorter mean duration of disease in the Reykjavik Study cohort, and thus underestimation of the mortality rate of diabetic persons in that cohort.
In the Northern Sweden Monica Study  it was observed that long-term survival after a first myocardial infarction in middle age was markedly lower in diabetic patients than in those without diabetes. Similarly, the long-term survival after the first stroke was much lower in diabetic patients than in those without diabetes , although survival did improve throughout the period from 1985 to 2005. The decline in relative mortality due to diabetes seen between 1996 and 2006 in the UK  possibly resulted from both improved trends in the incidence of and mortality from cardiovascular disease and improved medical attention. In Denmark reduced rates of death and cardiovascular disorders were observed in patients with type 2 diabetes in the Steno-2 Study using intensive intervention with multiple drug combinations . Although a general trend towards improved survival of patients with diabetes compared with those without diabetes is illustrated in these studies the survival gap still persists.
Another finding of our study was the increase in recorded history of acute cases of coronary heart disease seen between the two periods, in both those with and without diabetes. This is probably due to the increased survival rate of coronary heart disease patients, following the favourable changes in cardiovascular risk factor levels in all age groups, possibly resulting in milder disease, but an increase in hospital referral between study periods cannot be excluded. More intensive medical intervention has also tended to reduce premature deaths from coronary heart disease, especially from myocardial infarction, as was observed in Iceland during the period 1981 to 2006 in the age group of 25–74 years .
Regarding the changes in medication over the study period, we have shown in a previous study that statin use, irrespective of glucose-lowering or antihypertensive medication, is associated with lower mortality rate of older individuals with type 2 diabetes compared to those without diabetes . In 1993 statin therapy had not been introduced and their general use in 2004 could explain some of the drop in mortality rate observed between the study periods.
The Icelandic population is comparable to other Western populations with respect to cardiovascular morbidity and mortality , and the low prevalence of diabetes in Iceland has been changing similarly to trends in other Western societies . Our data show that the life expectancy of older individuals diagnosed with type 2 diabetes has increased concomitantly with that of the population in general, and that reductions in cardiovascular risk factors and improved treatment modalities may have benefited them at least as much as those without diabetes.
The strengths of the present study are the proportionally large national representation of older individuals in this population-based study, the high participation rate and the comprehensive information available on morbidity and mortality. It was observed that frailer individuals participated to a lesser extent, causing a possible bias, but non-attendees in this study have been shown to have comparable levels of conventional cardiovascular risk factors  during earlier visits. A weakness of this study is that the diagnosis of diabetes at baseline was based on a single measurement of fasting glucose (≥ 7 mmol/l), thereby possibly causing a positive bias in the number of persons diagnosed at entry ; this may also have caused a dilution bias in the estimates of mortality rates. Those developing diabetes after having answered the questionnaire will have been missed, which may have caused a slight bias in the mortality estimates. The power of the data was not enough to make stratifying for sex statistically significant and may be listed as a weakness. Prevalent coronary heart disease only included acute myocardial infarction cases and coronary procedures. Accordingly, subjects with angina were not included, causing a possible classification bias.