Intense treatment to lower blood sugar in patients with diabetes could prove nearly as harmful as allowing glucose levels to remain high, a study says.

Cardiff researchers looked at nearly 50,000 patients with type 2 diabetes and found the lowest glucose levels linked to a heightened risk of death.

Significant differences in death rates between patients on insulin and those taking tablets are also flagged up.

But there could be various explanations for this, experts noted.

Patients taking insulin-based treatments have been urged not to stop taking their medication as a result of the Cardiff University study, which is published in The Lancet.

Changing treatments

Using data from GPs, the team identified 27,965 patients with type 2 diabetes whose treatment had been intensified to include two oral blood glucose lowering agents - metformin and sulphonylurea.

A further 20,005 patients who had been moved on to treatment which included insulin were added to the study.

Patients whose HbA1c levels - the proportion of red blood cells with glucose attached to them - were around 7.5%, ran the lowest risk of dying from any cause.

For both groups this risk went up by more than half if levels dropped to 6.4%, the lowest levels recorded. For those with the highest levels the risk of death increased by nearly 80%.

But the risks appeared to be particularly pronounced among those on the insulin-based regimen than those on the combined treatment.

Irrespective of whether their HbA1c levels were low or high, there were 2,834 deaths in the insulin-taking group between 1986 and 2008, nearly 50% more than in the combined group.

'Don't stop'

The authors acknowledged there could be various factors associated with this, such as these being older patients with more health problems, who perhaps had had diabetes for a longer period of time. They also make reference to a possible link between use of insulin and cancer progression that had been reported in a different study.

"Whether intensification of glucose control with insulin therapy alone further heightens risk of death in patients with diabetes needs further investigation and assessment of the overall risk balance," wrote lead author Dr Craig Currie.

"Low and high mean HbA1c values were associated with increased all-cause mortality and cardiac events. If confirmed, diabetes guidelines might need revision to include a minimum HbA1c value."

Dr Iain Frame, head of research at Diabetes UK, described the study as "potentially important" but stressed it had limitations.

"It is not clear what the causes of death were from the results reported. Furthermore, when it comes to the suggestion made in this research that insulin could increase the risk of death, we must consider important factors such as age, the duration of their diabetes and how the participants managed their condition.

"It is crucial to remember that blood glucose targets should always be agreed by the person with diabetes and their healthcare team according to individual needs and not according to a blanket set of rules."

While people would be able to manage their condition for a period with diet, exercise and even tablets, many would eventually have to move on to insulin, he noted.