But researchers said glucose levels should be managed in all patients, and younger patients and those with newly diagnosed disease may benefit from intensive early treatment.
Professor Andrea Siebenhofer-Kroitzsch of the institute for general practice at Goethe University in Frankfurt, raised her concerns at the European Association for the Study of Diabetes (EASD) meeting in Vienna, Austria, last week.
'Intensity of glucose treatment should depend on the age of the patient,' she said.
Younger patients may benefit more from strict blood glucose control, but 'for older patients, less stringent values might be appropriate', she added.
Professor Siebenhofer-Kroitzsch said her research did not support the QOF target for achieving HbA1c levels below 7 per cent in older patients.
'If you calculate absolute numbers, such as NNT for the prevention of MI, you have to treat several hundred patients to prevent one patient from experiencing one.'
Patients treated to the lower targets would have to accept a doubled risk of hypoglycaemia, risking unconsciousness or coma, she pointed out.
Older patients should be told that they may not benefit, and could then decide what to do, she said. But she stressed that younger patients should be 'strictly treated' to prevent MI.
Fellow researcher Thomas Pieber of Graz University, Austria, said the findings left clinicians in 'a difficult situation'.
'The simple message that we love so much - that lower is better - is not working,' he said. But he stressed that the researchers were not calling for all glucose treatment to stop. 'We are only saying that the view that 'lower is better' is without scientific evidence. Diabetes treatment has to be improved, not got rid of.'
