Resveratrol is a polyphenolic phytoalexin. It is also classified as a stilbenoid, a derivate of stilbene, and is produced in plants with the help of the enzyme stilbene synthase. The levels of resveratrol found in food vary greatly. Red wine contains between 0.2 and 5.8 mg/L depending on the grape variety, while white wine has much less. The reason for this difference is that red wine is fermented with grape skins, allowing the wine to absorb the resveratrol, whereas white wine is fermented after the skin has been removed. Resveratrol is also sold as a nutritional supplement. A number of beneficial health effects, such as anti-cancer, antiviral, neuroprotective, anti-aging, anti-inflammatory, and life-prolonging effects have been reported for resveratrol. The fact that resveratrol is found in the skin of red grapes and as a constituent of red wine may explain the "French paradox". This paradox is based on the observation that the incidence of coronary heart disease is relatively low in southern France despite high dietary intake of saturated fats. Resveratrol is thought to achieve these cardioprotective effects by a number of different routes: (1) inhibition of vascular cell adhesion molecule expression; (2) inhibition of vascular smooth muscle cell proliferation; (3) stimulation of endothelial nitric oxide synthase (eNOS) activity; (4) inhibition of platelet aggregation; and (5) inhibition of LDL peroxidation (PMID: 17875315 , 14676260 , 9678525 ). Resveratrol is a biomarker for the consumption of grapes and raisins.