A large cohort study has found that lower systolic blood pressure (BP) is associated with reduced cardiovascular risk in type 2 diabetes patients with no previous cardiovascular disease (CVD). However, there was evidence of a J-shaped relationship between systolic BP and heart failure, and also all cause mortality.

The retrospective population-based cohort study used data on patients who entered the Swedish national diabetes register between 2006 and 2012. Criteria for inclusion were patients aged up to 75 years with type 2 diabetes for at least a year but no previous CVD or other major comorbidity. A total of 187,106 patients were eligible for inclusion, and the mean duration of follow-up was five years.

Outcome measures were obtained from hospital discharge and death registers. Hazard ratios (HR) were estimated for different levels of baseline BP and adjusted for potential covariates. Systolic BP was divided into six categories: 110-119 mmHg;120-129 mmHg; 130-139 mmHg;140-149 mmHg; 150-159 mmHg and ≥ 160 mmHg.

Compared with the reference group (130-139 mmHg) the group with the lowest systolic BP (110-119 mm Hg) had significantly lower risks of:

• Non-fatal acute MI; HR 0.76

(95% CI: 0.64-0.91)

• Total acute MI; HR 0.85

(95% CI: 0.72-0.99)

• Non-fatal CVD; HR 0.82

(95% CI: 0.72-0.93)

• Total CVD; HR 0.88

 (95% CI: 0.79-0.99)

• Non-fatal CHD; HR 0.88

(95% CI: 0.78-0.99)

There was no evidence of a J-shaped relationship between systolic BP and these endpoints. However, there was evidence of a J-shaped relationship between systolic BP and heart failure, and also all cause mortality.

The authors conclude that by adjusting for comorbidities, mainly by excluding patients with previous CVD, the J curve relation between systolic BP and MI and CHD disappears.

They postulate that the association between low BP and increased mortality might be caused by concomitant disease, rather than by antihypertensive treatment.

However, the authors caution: ‘One limitation of our study is that it did not include individuals with complications or those over 75. We believe that caution should be exercised when using observational studies to draw conclusions about recommended treatment goals for blood pressure among high risk patients.’

The debate is ongoing on optimum systolic BP targets. It may be that the way forward for systolic BP targets will turn out to be the same as for HbA1c levels i.e. individual targets, depending on the age, duration of diabetes, and comorbidities.

Dr Matthew Lockyer