Long-term follow-up data from a landmark trial indicates that intensive glycaemic control reduces the risk of long-term hypertension compared to conventional control.

Diabetes is a risk factor for hypertension, however it is uncertain to what extent this is due to hyperglycaemia rather than obesity or hyperinsulinaemia, and there have been concerns raised that the modestly increased amounts of insulin needed for intensive control might increase the risk. The Diabetes Control and Complications Trial (DCCT) was a landmark study that showed intensive control of type 1 diabetes to be associated with significantly better outcomes over the 6.5 year trial follow-up. Patients in DCCT have been followed-up observationally in an extension study, Epidemiology of Diabetes Intervention and Complications (EDIC), and overall, participants have been followed-up for over 20 years with regular monitoring of blood pressure and other clinical characteristics. This analysis examined whether there has been any difference in hypertension rates between those allocated originally to intensive or conventional control. For the purpose of this analysis, incident hypertension was defined as 2 consecutive study visits with a systolic blood pressure of 140 mm Hg or higher, a diastolic blood pressure of 90 mm Hg or higher, or use of antihypertensive medications to treat high blood pressure.

Participants in DCCT were recruited between August 1983 and June 1989; at the end of the study, in 1993, they were invited to join EDIC, and 1,375 (96.3%) of the surviving cohort (1,428) agreed to do so. This analysis includes data up to 2005 (the 12th year of EDIC). At the end of DCCT, the difference in HbA1c levels between the two groups was about 2%, and over the course of follow-up this difference disappeared. Just over 10% of the cohort was lost to follow-up to leave 1,441 for final analysis.

Over the whole course of follow-up from the start of DCCT (median 15.8 years), 630 of the 1,441 patients had developed hypertension. During DCCT itself, the incidence of hypertension was not statistically different in both intensive and conventional groups. Over the EDIC follow-up, however, assignment to intensive therapy in the original study was associated with a significant reduction in risk of developing hypertension with a relative risk reduction of 24% (hazard ratio, 0.76; 95% CI, 0.64 to 0.92). When the whole study period was included, the relative risk reduction was 20% (HR 0.80; 95% CI, 0.69 to 0.94).

The authors conclude that their results show hyperglycaemia to be a risk factor for hypertension in type 1 diabetes, and that intensive glycaemic control using insulin can reduce this risk. They comment that the effect was distinct despite blood glucose control converging in the two groups after the end of the study. They discuss some of the study's potential limitations, noting also its strengths of long follow-up, low loss to follow-up, and frequent clinical measurements.