In cystic fibrosis diabetes, higher long-term blood sugar was linked to more deaths

Death rates rose step by step with higher HbA1c in 4,477 people with cystic fibrosis-related diabetes in a UK registry study published Oct. 26, 2026, in Diabetes Care, up to a rate ratio of 1.93 above 69 mmol/mol compared with 42 or below. Keeping blood sugar in range matters in this form of diabetes.

Cystic fibrosis is a genetic disease that mainly affects the lungs and digestion. As people with cystic fibrosis live longer, many develop a special type of diabetes, cystic fibrosis-related diabetes, which is linked to a higher risk of death. But it wasn’t clear how much blood sugar control over time matters.

The higher the long-term blood sugar, the higher the death rate.

What did the study look at?

Researchers followed 4,477 people with cystic fibrosis-related diabetes, adding up 31,311 person-years of follow-up, during which 758 died. They tracked HbA1c, a measure of average blood sugar over recent months, and adjusted for age, calendar year, sex, body mass index, lung function and use of CFTR modulators, newer drugs that treat the underlying defect.

What did the study find about blood sugar?

Mortality rose progressively with each higher band of HbA1c.

Why does this matter?

Diabetes management in cystic fibrosis is different from type 1 or type 2 diabetes, and targets aren’t always clear. This study suggests that keeping average blood sugar lower over time is linked to better survival, which supports paying close attention to glucose in cystic fibrosis care.

How solid is this evidence?

It’s moderate. Mongevity rates it C on our A-to-E scale. The registry is large and long, and the analysis adjusted for key factors such as lung function. But it’s observational: people with higher HbA1c may be sicker in other ways, so it doesn’t prove that lowering blood sugar would prevent deaths.

What does this mean for you?

If you or someone close to you has cystic fibrosis-related diabetes, ask the care team what HbA1c target makes sense and how often it should be checked. Treatment usually involves insulin and is tailored with the CF team, because nutrition needs in cystic fibrosis are different.

How do I explain this at dinner?

Some people with a lung condition called cystic fibrosis also develop diabetes. Scientists looked at thousands of them and saw that those with higher sugar levels over time were more likely to die. A good question for the table: why might keeping something steady over time matter more than one day’s result?

In one sentence: in people with cystic fibrosis-related diabetes, higher long-term blood sugar was linked to progressively higher death rates.