Researchers from Imperial College, London, found that ethnic minorities are not only more likely to suffer from diabetes, but are also expected to have worst outcomes of lower quality care.
In particular diabetes control and care was shown to be "significantly worse" in south Asians.
The researchers studied the treatment received in 2002 by 21,343 diabetic patients in three north-west London primary care trusts (PCTs): Ealing, Hammersmith and Fulham, and Hounslow.
The study, published in the International Journal for Equity in Health, says that although diabetes control was worse among south Asians, a smaller proportion of this group were prescribed insulin.
And even though the white population studied was older, blood pressure differences between the groups were small. This, the researchers claim, points to poorer control in non-white ethnic groups.
They propose that the poorer quality of care for Asian diabetic patients could be due to the standard of care offered by General Practitioners or because of patient factors - such as poor understanding of the disease.
Institutional racism is unlikely as many south Asians are registered with GPs from their own ethnic group, the researchers conclude.
"This study highlights the need to capture ethnicity data in clinical trials and in routine care, to specifically investigate the reasons for these ethnic differences. But we don't just need to know more about both the practice and patient factors involved," said researcher Dr Michael Soljak.
"There should be more intensive management of diabetes and education about the disease in south Asian patients. The best option would be trials comparing different types of such interventions. Our study also shows that in future these trials can be carried out using routinely collected clinical information," he added.