Hypertension
Hypertension is one of the most relevant clinical findings for public health policy, with a global prevalence of 26 % in the adult population in 2000. Twenty-nine percent were projected to have this condition by 2025 [46]. About 90 % of subjects with hypertension suffer from essential hypertension, that is, hypertension is not the consequence of another disease. Due to the increased risks of stroke and CHD [47], and also of renal cancer [48] associated with hypertension, lifelong medication is usually required. It could be shown that even a slight reduction in the mean blood pressure in the population strongly reduces the incidence of cardiovascular diseases [49, 50]. The American Heart, Lung and Blood Institute has stated in 2003 that the measures for the prevention of hypertension include a health-promoting lifestyle which in addition to weight reduction (at existing overweight) comprise the adherence to the DASH diet,5 the limitation of sodium and alcohol intake as well as increased physical activity [51]. The ESH–ESC Task Force on the Management ofArterial Hypertension [52] of the European Society of Hypertension regards the increase in the consumption of vegetables and fruit as one of the lifestyle measures that can lower blood pressure in individuals with only a few risk factors for cardiovascular diseases and slightly increased blood pressure.
The INTERSALT Study with data of more than 10,000 subjects from 52 centres in 32 countries has shown an inverse relation between the intake of potassium (a mineral associated with a plant-based diet high in vegetables and fruit) and blood pressure, independent of the quantity of sodium intake [53]. However, in a small tightly controlled intervention study over 6 weeks including 48 participants with slightly increased blood pressure, such an effect could not be shown [54].
In vegetarians, there is often a lower blood pressure observed than in the total population, and a reduction in the blood pressure has been seen after changing from a normal to a vegetarian diet [55]. In cohort studies, there were either inverse relations between the consumption of vegetables and fruit and new cases of hypertension [56, 57] or inverse relations with one of the two food groups considered here or with a dietary pattern including vegetables and fruit [58, 59]. In the cross-sectional and in the longitudinal analysis of theSU.VI.MAX Study, an inverse relation was observed between vegetable and fruit consumption and blood pressure [60]. There was no relation seen regarding other components of the DASH diet. The intervention with antioxidant vitamins did also not influence the development of blood pressure. In the SUN cohort studyin turn, it was observed that a high consumption of vegetables and fruit was only associated with a reduced risk of hypertension, if the consumption of olive oil was low (<15 g/day) [61]. Another analysis of the Nurses’ Health Study (NHS) I and II and the Health Professionals Follow-up Study (HPFS) after 14 years of follow-up with flavonoid intake calculated by an updated nutrient database from 2010 showed a risk reduction in hypertension with increasing intake of anthocyanins [62].
The DASH diet is based upon the DASH Study, which is a randomised 8-week intervention study including 459 hypertensive patients. One intervention group was instructed to eat a diet rich in vegetables and fruit, and the other group got the same instructions with additional information on a diet low in fat and high in dietary fibre. In both intervention groups, a lowering of blood pressure was reported [63]. In the latter group, the blood-pressure-lowering effect was more pronounced than in the group that was only instructed to eat a diet rich in vegetables and fruit. Other intervention studies have confirmed the effectiveness of the DASH diet as measure for reducing blood pressure levels. For example, the DASH intervention in the Premier Trial Study including 810 adults with hypertension achieved a greater decrease in blood pressure levels by an increased consumption of vegetables and fruit as well as of low-fat dairy products than the intervention with weight reduction, enhanced physical activity, and limitation of sodium intake [64]. In children and adolescents, too, this diet is suitable to lower blood pressure levels [65]. A 6-month intervention study including 690 subjects at the age of 25–64 years in England confirmed the results of the DASH study [66]. In this study, an increase in the consumption of vegetables and fruit to at least 5 portions/day was accompanied by a lowered blood pressure. Furthermore, the study showed that an increase in vegetable and fruit consumption does neither lower the blood cholesterol concentration nor leads to weight loss, but keeps weight stable. An intervention study conducted in the 1990s including 78 participants with low consumption of vegetables and fruit (<3 portions/day) revealed that lipid and lipoprotein metabolism are not influenced by an increase in vegetable and fruit consumption [67].
Based on the present data, the evidence regarding a blood-pressure-lowering effect of an increase in the consumption of vegetables and fruit is judged as convincing. Both cohort and intervention studies show consistent results.
Coronary heart disease
Coronary heart disease (CHD) is the most important manifestation of arteriosclerosis in humans and belongs to the large group of cardiovascular diseases. CHD is still the single largest cause of premature death in the world. Ischaemic heart disease has been estimated to account for 12 % of all deaths worldwide in 2004 [68]. In 2008, 17 million deaths worldwide were due to cardiovascular diseases, accounting for 48 % of non-communicable disease deaths [69]. While CHD death rates have declined in many parts of the industrialised world, death rates are increasing in most developing countries [70]. CHD is also a major cause of disease burden in terms of disability-adjusted life years lost (DALY), accounting for 63 million DALYs worldwide in 2004 [68].
In addition to age and gender, modifiable risk factors are important, especially lifestyle factors like smoking and a lack of physical activity and the medical diagnoses hypertension, diabetes mellitus, obesity, and dyslipoproteinaemia [71]. Among these factors, the 4 medical diagnoses are clearly nutrition-related and can be influenced by a change in nutrition. Other biological mechanisms that are probably important in atherogenesis are influenced by nutrition, including inflammatory processes, oxidative stress, and increased homocysteine concentrations [72].
Several prospective cohort studies that investigated whether the consumption of vegetables and fruit is associated with the risk of CHD were summarised in 2 meta-analyses. In the meta-analysis by Dauchet et al. [73], which included 9 cohort studies, the risk of CHD was reduced by 4 % (RR 0.96; 95 % CI 0.93–0.99) per portion of vegetables and fruit and by 7 % (RR 0,93; 95 % CI 0.89–0.96) per portion of fruit daily. For vegetables, the inverse relation regarding the risk of CHD was stronger for the overall cardiovascular mortality (RR per portion 0.74; 95 % CI 0.75–0.84) than for fatal or non-fatal myocardial infarction (RR 0.95; 95 % CI 0.92–0.99). Between mortality and consumption of fruit as well as total intake of vegetables and fruit, a linear dose–response relation was observed. In contrast, the relation between mortality and consumption of vegetables was nonlinear. The meta-analysis of He et al. [74] included 13 cohort studies. Compared with individuals who consumed <3 portions of vegetables and fruit per day, persons with a consumption of 3–5 portions per day (RR 0.93; 95 % CI 0.86–1.00) and of >5 portions per day (RR 0.83; 95 % CI 0.77–0.89) had a lower risk of CHD. Subanalyses revealed a significant inverse relation with the risk of CHD both for fruit and for vegetables. In the following years, after the publication of these meta-analyses, the result of other cohort studies was published. A higher vegetable and fruit intake was inversely associated with the risk of CHD in the EPIC-Heart Study [75], the Morgen Study [76], a Swedish [77], and a Japanese cohort [78], while in the Italian arm of the EPIC Study, no association was found for vegetables and fruit in total, but for leafy vegetables [79]. These data are also reflected in the judgement of the WHO [80] and current nutritional recommendations of the European Society of Cardiology [71] and the American Heart Association [81] that both recommend the consumption of vegetables and fruit to reduce the risk of CHD.
However, the results of the WHI Dietary Modification Trial (see “Obesity”) suggest that an additional portion of vegetables and fruit daily does not influence the risk of CHD [82]. As the primary objective of this multiple intervention is a reduction in fat intake, the significance of this study regarding the assessment of the benefit of vegetable and fruit consumption is limited.
The data on the outcome “CHD” are supplemented by intervention studies that have investigated intermediary clinical markers of the cardiovascular system when offering specific kinds of vegetables and fruit. These studies showed that the consumption of vegetables and fruit can improve the regulation of blood vessel enlargement [83], prevent platelet aggregation [84–86], and reduce inflammation markers [87, 88].
In summary, it can be concluded that many cohort studies on this question have been performed, and most of the cohort studies have shown a protective association between the consumption of vegetables and fruit and the risk of CHD. In addition, there are intervention studies that prove a beneficial influence of vegetables and fruit on metabolic pathways that are associated with the risk of CHD. Therefore, the evidence regarding the prevention of CHD by high consumption of vegetables and fruit is judged as convincing.
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