More Fruits & Vegetables Improve Arterial Function

Cardiovascular disease (CVD) is believed to start with damage to the inner lining of the arteries. This lining is known as the endothelium. The endothelium releases chemical signals that can dilate blood vessels and increase blood flow when needed. The endothelium?s ability to dilate its surrounding muscle layer with chemical signals such as nitric oxide can be compromised by inflammation, elevated blood fats, the stress of increased blood pressure and/or perhaps electrolyte changes.

Factors that compromise the function of endothelium in the short run are also known to increase the chances for CVD events in the longer term. A well-established measure of endothelium function is called flow-mediated dilation (FMD), which measures the ability of blood vessels to dilate in response to intravenous injection of chemical signals such as acetylcholine. Previous research has shown even a single fat-rich meal can impair FMD for several hours compared to an isocaloric low-fat meal.1 More recently reducing salt/sodium in the diet from 3,600 to 1,500 mg per day improved FMD by 45% in just a few weeks in normotensive subjects (see March 2009 CFFH for details). Dietary fat may impair FMD at least in part by increasing inflammation perhaps due to toxins absorbed along with the fat from the gut (see Feb. 2009 CFFH for details).British researchers looked at the impact of consuming more fruits and vegetables on FMD in 117 hypertensive subjects 40-65 years old. Subjects were randomly assigned to 3 groups that were instructed to eat 1, 3 or 6 standard servings of fruits and vegetables daily for 8 weeks. Dietary compliance was assessed with 4-day food logs during weeks 4 and 8 and also by measuring the levels of vitamin C and several carotenoids in their blood. The authors conclude ??among hypertensive participants, there is a dose-response relationship between fruit and vegetable consumption and endothelium-dependent vasodilation, ?.?2 This study found each additional serving of fruit or vegetable consumed daily improved FMD by about 6% or about 30% improvement for an extra 5 servings. The results of this study may help explain why prospective cohort studies have found a reduced risk of coronary heart disease3 and stroke4 in people who eat more fruits and vegetables.Precisely how eating more fruits and vegetables may have improved endothelial function in this study is not known. The increased intake of vitamin C, carotenoids, polyphenols, and other phytochemicals found in fruits and vegetables may help protect the endothelial cells from the damaging effects of postprandial lipemia, endotoxins, and increased plasma sodium levels. In addition, the increased potassium intake from extra fruits and vegetables may also mitigate the damage from excessive salt intake. It is also possible that subjects who ate more fruits and vegetables modestly reduced their intake of fat and salt. Nevertheless, the results of this study clearly show that instructing people to eat more fruits and vegetables is likely to improve their endothelial function and cut their risk of CVD events in the future.Bottom Line:It seems increasingly clear that the typical modern diet high in fat and salt impairs FMD by compromising the ability of the endothelium to function properly. By contrast, this recent study has shown when hypertensive people eat more fruits and vegetables they dramatically improve the FMD response in their arteries.By James J. Kenney, PhD, RD, FACNReferences:1. Am J Cardiol. 1997;79:350-3542. Circulation 2009;119:2153-603. J Nutr 2006;136:2588-934. Lancet 2006;367:320-6