Diabetes and Hypertension

Hypertension occurs more often in patients with diabetes
than in individuals without diabetes. This 1.5–2-fold excess
of hypertension can be accounted for by several clinical and
pathophysiological factors including diabetic nephropathy,
altered neuroendocrine and sodium-volume determinants of
blood pressure, disturbed vascular tone and altered blood
pressure regulation (Figure 1). Hypertension is also a major
cause of diabetic nephropathy. The prevalence of hypertension
in type 2 diabetes has been reported to be 30–80%.
In type 1 diabetes, the prevalence is up to 25%, and hypertension
is usually seen in association with nephropathy.
Importance of hypertension in diabetes
Hypertension is important in diabetes mellitus because it accelerates
both macrovascular (ischaemic heart disease, stroke,
peripheral arterial disease, heart failure) and microvascular
complications. The presence of proteinuria (i.e. diabetic
nephropathy) is associated with a marked increase in overall
mortality from cardiovascular disease and end-stage renal
failure. Most diabetic complications occur in association with
hypertension. Cardiovascular complications account for up
to 75% of mortality in patients with type 2 diabetes.
What level of blood pressure requires treatment?
The most recent guidelines (Figure 2) have incorporated findings
from the major hypertension intervention trials that have
data specific for patients with diabetes (Figure 3).
In the UK Prospective Diabetes Study (UKPDS), patients
with type 2 diabetes (mean age 56 years) were treated for
8.4 years with either a β-blocker or an angiotensin-converting
enzyme (ACE) inhibitor-based regimen to achieve ‘tight’ blood
pressure control (mean 144/82 mm Hg). Compared with less
tight control (mean 154/87 mm Hg), there were significant
reductions in diabetes-related deaths (32%), stroke (44%),
heart failure (56%) and progression of retinopathy (37%), despite
drug side-effects and compliance problems. This study
showed that the clinical benefit of reducing blood pressure by
10/5 mm Hg was greater than that of intensive glucose lowering.
The lower blood pressure required mainly combination
therapy and not any specific single-drug treatment, there
was no threshold or ‘J-shaped’ effect of treatment, and the
benefits of treatment exceeded the benefits expected from
epidemiological data.
The Hypertension Optimal Treatment (HOT) study con-
firmed a reduction in cardiovascular events with combination
treatment, based on a calcium channel blocker (felodipine)
regimen. Treatment targets were diastolic blood pressure less
than 80 mm Hg, less than 85 mm Hg and less than 90 mm Hg.
The 4 mm Hg difference between the less than 80 mm Hg and
less than 90 mm Hg target groups was associated with a 51%
reduction in major cardiovascular events and a 67% reduction
in cardiovascular mortality. New findings were the additional
cardiovascular benefit of the addition of aspirin,
75 mg, and the safety of calcium channel blocker therapy.
Management
Non-drug treatment (Figure 4)
In combination with maximal diabetic control and attention
to other cardiovascular risk factors, non-drug treatments
(weight loss for obesity-related hypertension and aerobic
exercise) confer benefit. Reduction in dietary sodium intake
significantly reduces both systolic and diastolic blood
pressure.