High blood pressure and diabetes: big gaps in knowledge regarding non-drug treatment strategies

Rapid report: Special diets in people with essential hypertension (DASH diet)

The Dietary Approaches to Stop Hypertension (DASH) diet combines a diet rich in fruit and vegetables with dairy products. It is rich in natural minerals, fibre and low-fat dairy products, but low in saturated fats. Particularly recommended are whole grain products, fish, poultry and nuts.

The DASH diet goes back to a 1995 study that investigated the effects of the food we eat on high blood pressure (hypertension). However it did not permit any long-term conclusions. In its report on the benefit of the DASH diet, IQWiG compared it with no special diet or another blood pressure-lowering intervention in patients with essential hypertension. Patient-relevant outcomes were just as important in this investigation as other outcomes such as blood pressure control (change in blood pressure or antihypertensive medication).

No results for patient-relevant outcomes

There were a total of 12 scientific publications, all of which could be rated as high-quality (randomized controlled trials, RCTs). For the benefit assessment, two groups were compared: in one group, patients with high blood pressure were treated with a complex behavioural therapy that aimed to reduce calorie, salt and alcohol intake and increase physical activity. The second group received the same therapy and in addition, advice about the DASH diet.

No information was provided on the patient-relevant outcomes of death from any cause (all-cause mortality), deaths from or rates of cardiovascular disease (cardiovascular mortality and morbidity), failure of kidney function (end-stage renal disease), health-related quality of life or side effects. Results were only available for the outcomes "Duration and extent of the change in blood pressure" and "Changes in antihypertensive (blood pressure-lowering) medication", but no proof or indication of a benefit or harm could be derived from these.

Overall, the data therefore provide no scientific proof of a benefit or harm from the DASH diet for people with essential hypertension.

Rapid report (German version)

Rapid report: Stress-coping interventions in people with essential hypertension

IQWiG considered RCTs lasting at least 24 weeks for its report. In these trials, patients were taught how to cope better with stress, e.g. through behavioural training or relaxation techniques. The comparator group did not participate in such a programme. The measure used to assess effectiveness in the 16 studies included was the change in blood pressure itself, or the change in dosage of blood pressure-lowering drugs (in each case with or without stress reduction).

With 9 to 72 adult participants, the groups in the relevant studies were rather small. The studies lasted 6 to 60 months - in most cases, 12 months. Most of them were published in the 1970s and 1980s. With one exception, the risk of bias in all of the study results was very high, so that misinterpretations of the results are possible.

Data on patient-relevant outcomes non-existent or inadequate

The extremely heterogeneous studies provided no or only inadequate data on patient-relevant outcomes of all-cause mortality, cardiovascular mortality and morbidity, end-stage renal disease, health-related quality of life, and side effects of interventions (e.g. counter-reactions in imaginative relaxation exercises).

Overall, it is therefore unclear whether stress-coping interventions have a perceptible advantage or disadvantage for people with essential hypertension.

Rapid report (German version)

Rapid report: Alcohol reduction in people with essential hypertension

For this report, IQWiG searched for RCTs in which people with high blood pressure and high alcohol consumption (but not alcoholics) were treated with the aim of reducing their alcohol intake by the use of various treatment strategies. Effects on blood pressure were to be observed: one group of participants was asked to drink less alcohol. In the comparator group, alcohol consumption was not to be reduced, or only to a small extent. Study participants were to have been monitored for at least 24 weeks.

In the end, IQWiG could only include two studies in the assessment. Since not all participants also suffered from high blood pressure, IQWiG could only include the data of about 400 participants. Both studies were prone to a high risk of bias, which greatly restricts the informative value of the results.

Studies provide no or inadequate data

The studies provided no or inadequate data concerning mortality, late complications of high blood pressure affecting the heart and blood vessels, or quality of life and side effects. That means there is no proof that the intervention had a perceptible advantage for the patients.

There was also no proof in respect of the reduction in blood pressure. Likewise unanswered is the question whether patients who drink less actually require fewer blood pressure-lowering drugs: at any rate, there were no differences between the treatment groups.

Rapid report (German version)

Rapid report: Cessation of smoking in people with essential hypertension

There is no doubt that smoking is an important risk factor for increased mortality and an increase in cardiovascular risk. Many other harmful effects of smoking tobacco are recognized.

The IQWiG report investigated the benefit of interventions to stop smoking compared to no such intervention in patients with essential hypertension. Patient-relevant outcomes as well as outcomes of blood pressure control were relevant.

No studies available on the effects of cessation of smoking in people with essential hypertension

There are indeed high-quality studies (RCTs) that have investigated, over a very long period, the effects of an intervention to stop smoking compared to standard care without such an intervention, focussing on patient-relevant outcomes.

However, neither the search for primary literature in international databases nor in secondary literature or trial registries was successful: IQWiG could not find a single RCT anywhere in the world that has studied the effect of interventions to stop smoking in people with hypertension, focussing on patient-relevant outcomes such as mortality, morbidity or health-related quality of life. No study provided findings on an effect on blood pressure and the direct treatment of the hypertension.

Rapid report(German version)

Rapid report: Increase in physical activity in people with type 2 diabetes

In addition to dietary and pharmacological interventions, the guidelines of many national and international medical societies recommend physical activity in the form of endurance training and also strength training as the third pillar in the treatment of type 2 diabetes.

The IQWiG report examined interventions to increase physical activity in comparison with no such intervention in patients with type 2 diabetes, focussing on patient-relevant outcomes. Ultimately, 7 studies (RCTs) were used for the benefit assessment: 6 of them investigated the effect of a guided training programme over several weeks or months and in one study, independent training at home was investigated.

No results for patient-relevant outcomes

The study groups consisted of persons with a mean age of about 60 years and a mean body mass index (BMI) of more than 30. Studies lasted 6 to 24 months and, with one exception, all studies were regarded as potentially subject to a high risk of bias, i.e. their results are subject to uncertainty.

However, the studies provided no adequate data for a benefit assessment of increased physical activity in patients with type 2 diabetes in respect of the patient-relevant outcomes of all-cause mortality, cardiovascular mortality and morbidity, end-stage renal disease, amputations, severe episodes of hypoglycaemia (low blood sugar), blindness or impairment of vision due to changes in the retina. In addition, there is no indication or proof of an effect on health-related quality of life or side effects.

Rapid report (German version)

Rapid report: Long-term reduction in blood pressure to levels in the lower normal range in people with diabetes

High blood pressure is an important risk factor for cardiovascular diseases. IQWiG investigated whether a particularly marked reduction in blood pressure to levels in the lower normal range (below the standard values of 140 and/or 90 mmHg) in type 1 and type 2 diabetes can actually reduce the risk of heart attacks, strokes and other complications of diabetes such as kidney failure, amputation or blindness.

5 studies identified

In the 5 studies considered (4 RCTs on type 2 diabetes, 1 RCT on type 1 diabetes), adults with diabetes were observed for at least 6 months. In the intervention group, the aim was always to achieve a long-term reduction in blood pressure to the lower normal range. The aim of treatment in the comparator group was to achieve a standard value, but also lower blood pressure levels, provided they were above those of the intervention group.

The studies of greatest interest for the research question of the IQWiG report were those in which a target blood pressure for the systolic (upper) as well as the diastolic (lower) blood pressure value had been stated both for the intervention group and the comparator group. However, no such studies were available. The standard levels for both blood pressure values were not always achieved in the control groups. That should be borne in mind when interpreting results of the studies.

The only study on type 1 diabetes is subject to uncertainty

The results of the only study on type 1 diabetes are subject to great uncertainty because among other things, the data on patients were incomplete and it was unclear whether the study was blinded. This study only provided results on side effects (adverse events) and on an alternative criterion of effectiveness - a "surrogate outcome" (preliminary stages of end-stage renal disease). Thus it made no statements about mortality, symptoms and late complications or quality of life. On the basis of these results, a benefit or harm through the reduction in blood pressure to the lower normal range in people with type 1 diabetes is not proven.

Fewer strokes, but also aspects of harm in people with type 2 diabetes

Four studies on type 2 diabetes were included in the assessment. However, two were subject to great uncertainty, for example, because of unclear information about the study participants.

From the joint consideration of the 4 relevant studies, there is proof of a benefit from a reduction in blood pressure to the lower normal range for people with type 2 diabetes: fewer patients suffered a stroke.

However, the preliminary stages of end-stage renal disease (as shown by a change in serum creatinine) were overall seen more frequently in the study participants. Hence, harm is also proven in relation to a surrogate outcome.

Taken as a whole, there was no other proof or indication of a benefit or harm from the treatment for all other patient-relevant outcomes such as mortality, heart attack or heart failure. None of the relevant studies provided information on the patient-relevant outcomes of amputation, blindness or health-related quality of life either.

Separate consideration due to heterogeneous results

Because of differences in the overall results of the studies with target systolic and diastolic blood pressure regarding the patient-relevant outcomes of all-cause mortality, cardiovascular mortality, as well as two surrogate outcomes, for all of these outcomes the studies were also evaluated separately according to target blood pressure.

Each of the 3 studies in which the reduction in blood pressure was based on the diastolic blood pressure values provided an indication of lower mortality and less frequent changes to the fundus of the eye (surrogate outcome "preliminary stages of blindness") in those patients whose diastolic blood pressure values were to reach the lower normal range.

The study in which the systolic target value was less than 120 mmHg provided an indication of a negative effect of reducing blood pressure to the lower normal range for the surrogate outcome "preliminary stages of end-stage renal disease" (change in filtration rate in the kidneys). In addition, serious side effects occurred more frequently.

Rapid report (German version)

English-language executive summaries of the rapid reports will be available soon. If you would like to be informed when the English documents are available, please send an e-mail to info@iqwig.de.