Disparities in diabetes outcomes have widened despite improvements in insulin treatments over the past 30 years, according to a study published in Diabetes Technology & Therapeutics.

The study found that Mexican Americans who took insulin and achieved good blood-sugar control, defined as an A1C level below 7%, dropped from 25% during 1988 to 1994 to just 10% during 2013 to 2020. This group’s outcomes have increasingly strayed from those of non-Hispanic white adults, whose blood-sugar control has remained roughly the same, with about 33% achieving good blood-sugar control.

In recent years, 23% of Black adults and 24% of Mexican Americans—compared with only 9% of white adults—taking insulin have experienced hyperglycemia, or high blood sugar, characterized by an A1C level over 10%, according to the study.

The study also showed that patients have entirely different experiences while taking insulin, the primary treatment for people with type 1 diabetes and a vital therapy for those with type 2 diabetes. These differences persist despite the development of new insulin formulas and improved methods of administering the medication.

“What we want is for all these technologies and all these advances to improve public health,” said Elizabeth Selvin, a lead author of the study and a professor of epidemiology at the Johns Hopkins Bloomberg School of Public Health, in a news release. “What we’re actually seeing is a widening of disparities in diabetes.”

If periods of high blood sugar are prolonged, these disparities could lead to more serious complications, including kidney disease, vision impairment and nerve damage.

“The health care disparity has been very persistent for diabetes care,” said Frank Hu, a professor of nutrition and epidemiology at the Harvard T.H. Chan School of Public Health. “This is another indication that health disparities in the U.S. have actually exacerbated in the last one or two decades despite great efforts to reduce health disparities.”