Consumption of Fruit and vegetables prevents major diseases
Fruit and vegetable intake and the risk of cardiovascular disease, total cancer and all-cause mortality–a systematic review and dose-response meta-analysis of prospective studies
Fruit and vegetables are important components of a healthy diet. A sufficient daily consumption could help prevent and reduce the risk of major diseases, such as cardiovascular diseases and cancer. Approximately 1.7 million (2.8%) of deaths worldwide are attributable to low fruit and vegetable consumption. 1 A recently published WHO report recommends a minimum of 400g of fruit and vegetables per day (excluding potatoes and other edible starchy tubers such as cassava) for the prevention of chronic diseases such as heart disease, cancer, diabetes and obesity. 2 They conducted a systematic review and meta-analysis to clarify the strength and shape of the dose-response relationship between fruit and vegetable intake and risk of cardiovascular disease, cancer and mortality, and the effects of specific types of fruit and vegetables that are most strongly associated with a reduced risk of cardiovascular disease, total cancer or all-cause mortality and with regard to the burden of disease and mortality that may be attributed to a low fruit and vegetable intake.
A total of 142 publications from 95 unique cohort studies were included in the analyses. A systematic review and meta-analysis of published prospective studies relating fruit and vegetable consumption to risk of incidence or mortality from coronary heart disease, stroke, total cardiovascular disease, and total cancer, and to all-cause mortality were performed. They specifically aimed to clarify the strength and shape of the dose-response relationship for these associations and whether specific types of fruit and vegetables were associated with risk.
Researchers observed a reduction in risk of cardiovascular disease and all-cause mortality up to an intake of 800 g/day of fruit and vegetables. For the total cancer no further reductions in risk were observed above 600 g/day. Inverse associations were observed between intake of apples/pears, green leafy vegetables/salads, citrus fruits and cruciferous vegetables3and cardiovascular disease and mortality. As well between green-yellow vegetables and cruciferous vegetables and total cancer risk. On the other hand intake of tinned fruits was associated with increased risk of cardio-vascular disease and all-cause mortality.
Nowadays data regarding fruit and vegetable intake and cancer risk are less clear. But a modest association between fruit and vegetable intake or specific subtypes of fruits and vegetables and total cancer risk cannot yet be excluded. 4The included studies have been inconsistent. Some studies found no clear association, whereas other studies reported inverse associations. However, some of the studies that not found clear associations may have had statistical power too low to detect a modest association. Cohort studies have been more consistent in finding an inverse association between fruit and vegetable intake and risk of coronary heart disease and stroke than for cancer, and this has also been shown in previous meta-analyses as well as in several additional studies that have been published since these meta-analyses. Some of these cohort studies may have had statistical power too low too. Combining studies from different populations increases the sample size and statistical power, but also results in heterogeneity because of differences in the characteristics of the study populations. The results may have influenced by measurement errors in the assessment of fruit and vegetable intake. There was also a difference in serving per day between the studies. A high intake of Fruit and vegetable is often associated with other lifestyle factors such as lower prevalence of smoking, less overweight and obesity, higher physical activity and lower intakes of alcohol and red and processed meat, which could have confounded the observed associations. Many studies adjusted for confounding factors, but they found a little evidence that the results varied substantially whether or not adjustment for most of these confounders was done. It is possible that persons with a high fruit and vegetable intake may be more likely to undergo screening or have better access to or compliance with treatment. This could lead to an improved survival and bias the results for mortality.
Further studies are needed, because of the low number of studies on subtypes of fruit and vegatables, the potential for selective reporting and publication of subtypes that are significantly associated with risk. Moreover, studies are needed to clarify the association between fruit and vegetable intake and specific causes of death other than cancer and cardiovascular disease.