Diabetes-related deaths have fallen dramatically over the past 15 years in Canada and the U.K., but excess mortality persisted and was age dependent, a database analysis found.

In Ontario, the mortality rate ratio for diabetes declined from 1.90 (95% CI 1.86-1.94) in 1996 to 1.51 (95% CI 1.48-1.54) - a 44% decrease - according to Marcus Lind, MD, of the University of Gothenburg in Sweden, and colleagues.

And in the U.K. database known as The Health Improvement Network (THIN), the rate ratio fell by 43% to 1.65 (95% CI 1.57-1.72) from 2.14 (95% CI 1.97-2.32), the researchers reported online in Diabetologia.

Previous studies have yielded conflicting data on mortality rates among patients with diabetes.

In an effort to clarify this and to see if rates have changed over time, Lind and colleagues analyzed outcomes from large population-based databases in Ontario and the U.K.

They found that, between 1996 and 2009, the prevalence of diabetes in Ontario rose from 5.4% to 11.4%. In THIN, the increase was from 3.2% to 5.9%.

Mean age of patients with diabetes in Ontario was 60.8 years in 1996 and 61.5 years in 2009, while the ages in THIN were 62.7 and 63. Slightly more than half in both cohorts were men.

After adjustment for age and sex, the annual mortality rate declined from 19.4 to 12.2 per 1,000 individuals in Ontario, which was a 37.2% decrease.

The annual mortality rate decrease in THIN totaled 55%, falling from 31.4 to 14.1 per 1,000.

Among women in Ontario, there was a 47.1% decrease, from 1.94 (95% CI 1.88-1.99) to 1.48 (95% CI 1.45-1.52), while women in the U.K. cohort had a 49.6% decline, from 2.25 (95% CI 2-2.50) to 1.63 (95% CI 1.52-1.74).

Mortality among men in Ontario fell by 39%, from 1.87 (95% CI 1.82-1.93) to 1.54 (95% CI 1.50-1.58), and among men in the U.K. cohort by 35.6%, from 2.04 (95% CI 1.79-2.29) to 1.67 (95% CI 1.56-1.77).

Mortality rate ratios decreased over time for all age groups, but remained highest among patients ages 45 to 64.

In that age group, the rate ratio in Ontario was 2.48 (95% CI 2.35-2.61) in 1996 and 1.94 (95% CI 1.84-2.04) in 2009.

The corresponding rate ratios in THIN were 2.60 (95% CI 2.09-3.13) and 2.23 (95% CI 1.98-2.50).

The lowest mortality rate ratios were among patients ages 65 to 74, which decreased in the Ontario cohort from 1.45 (95% CI 1.41-1.50) in 1996 to 1.16 (95% CI 1.13-1.19) in 2006.

In that age group, the rate ratio in THIN fell from 1.46 (95% CI 1.29-1.63) to 1.24 (95% CI 1.17-1.30).

At both time points, the largest number of deaths were among patients older than 64. In Ontario, 84.6% of deaths in 1996 and 85.1% in 2006 were in that age group, while the percentages were 86.1% and 87.5% in THIN.

“Although caution should be exercised in identifying a trend-shift in the prognosis of patients with diabetes, more aggressive treatment during recent decades may be applicable to the present results,” Lind and colleagues observed.

Factors that may have contributed include the greater emphasis placed on glycemic control, lowering blood pressure, and use of statins.

However, the decrease in excess mortality also may relate to shorter duration of disease, the researchers pointed out.

Limitations of the study included a lack of information about diabetes type in the databases and some differences in design and data analysis in the two cohorts.

In addition, the findings may not be applicable to developing countries, where many cases of diabetes aren’t diagnosed and treatment resources are sparse.

“Further studies are needed to confirm these findings during contemporary time periods compared with historical estimates, and to include the type of diabetes and individuals in developing nations,” the researchers concluded.

Primary source: Diabetologia
Source reference: Lind M, et al “Mortality trends in patients with and without diabetes in Ontario, Canada and the UK from 1996 to 2009: a population-based study” Diabetologia 2013; DOI: 10.1007/s00125-013-2949-2.