Cranberry juice has long been known to have antioxidant properties attributed to high levels of polyphenols. While much research has been done concerning the impact of cranberries and cranberry juice on urinary tract infections, fewer studies have examined their effects on other pathologies. A recent study by Chew et al. examined the immediate and longer term effects of a cranberry juice extract on cardiovascular disease risk factors including; inflammation, glucoregulation, and oxidative stress. Healthy, overweight volunteers consumed either a high polyphenol cranberry juice extract or a placebo substitute. They were then assessed for biomarkers connected with inflammation, cardiovascular disease and oxidative stress over an eight-week test period. All blood sample results were normalized to hemoglobin concentration using the Arbor Assays Hemoglobin Colorimetric Detection Kit (K013-H).
Glucoregulation was examined using an oral glucose tolerance test. Glucose regulation was shown to be improved in the cranberry group as compared to the control, however the serum glucose concentrations were higher in both placebo and cranberry juice extract groups across all time points in the oral glucose tolerance test administered at week 8 as compared to week 1. This somewhat unexpected result requires more study, but it may suggest that the polyphenols from cranberry juice extract enhance sensitivity to insulin so that less insulin ultimately was required to the same amount of ingested glucose in the week 8 test. If proven out, this insulin sensitization could potentially impact long term management of patients with type 2 diabetes.
Oxidative stress and the enhanced oxidative modification of lipids, proteins and nucleic acids contribute to the pathogenesis of cardiovascular disease. Previous studies of the ability of cranberry juice to reduce levels of oxidized LDL have demonstrated mixed results, so Chew et al. looked at a number of different markers of oxidative stress to examine the question in finer detail. No effects were noted on circulating levels of oxidized LDL, urinary isoprostane levels, or levels of 8-OHdG as a marker of DNA oxidation. The initial week 0 dose of cranberry juice extract increased GSH:GSSH ratio in red blood cells by the same effect was not observed at week 8, suggesting that the effects of polyphenols on GSH are temporary. However, SOD activity was increased at the eight-week mark but glutathione peroxidase activity was not, suggesting that cranberry juice extracts do have some long term mitigating effects on oxidative stress levels
Levels of C-Reactive Protein (CRP), an important predictor of cardiovascular risk, were reduced after 8 weeks of daily cranberry juice extract, suggesting a reduction in systemic inflammation. So much so that CRP levels in the volunteers receiving the cranberry juice extract were low enough to classify them as being at low risk for cardiovascular disease based on guidelines from the American Heart Association and the CDC. Volunteers in the control group who consumed a polyphenol free placebo had CRP levels that placed them in the category of moderate risk of cardiovascular disease. Chew et al. also found that an acute dose of the cranberry juice extract increased nitric oxide and decreased levels of ET-1, suggesting a temporary benefit to vasodilation.
Although this study was relatively short term it did demonstrated that consumption of the cranberry juice extract reduced a variety of risk factors for cardiovascular disease. A second recent study by Galal et al. demonstrated that rats who consumed cranberry juice daily for 4 weeks showed a reduction in hepatorenal damage associated with cardiomyopathy (Arbor Assays FRAPTM Detection Kit, K043-H) . Further study is needed to determine if factors such as overall diet or genetics may influence the benefits of polyphenol enriched supplements in humans over the longer term.