conclusively state whether it could be a disease preventive substance in humans or could be used for human life extension (Table 1). It is therefore vital to perform such studies. Are there observed side effects caused by the intake of resveratrol in humans? Based on animal studies, Resv is generally well tolerated, and only very few short-term or acute exposure experiments in humans have been performed. When eight healthy subjects were exposed to 2000 mg Resv twice/day for eight days, six of eight subjects had mild episodic diarrhea/loose stool, typically in the beginning of the eight days treatment period, and one of the subjects developed a temporary rash and headache [9]. In a double-blinded, random- ized, placebo-controlled study, up to 975 mg/day were given to healthy volunteers, where two adult subjects (male and female) in each group were subjected to 25, 50, 100 or 150 mg, six times/ day, for two days in total. Adverse effects were mild in severity and similar between all groups. Repeated administration of Resv was well-tolerated but produced relatively low plasma concentrations of Resv, despite the high doses and short dosing interval used [10]. Exposure of up to 270 mg Resv to 19 volunteers for one week did not cause any discomfort [19]. According to Elliott et al. healthy volunteers tolerated Resv well in a seven-day exposure study, but experimental details were not provided thus making evaluation of results challenging [16]. The same article describes very briefly a study which included daily exposure to 2.5 g or 5 g Resv for 28 days. The authors reported that ‘‘Adverse events were generally mild in nature and reversible’’ but no experimental details are shown, which made a closer evaluation impossible [16]. The 20 colon cancer patients receiving 0.5 g or 1.0 g Resv daily for eight days before surgical resection [3] tolerated it well. It is difficult to estimate the normal human consumption of Resv as the intake of red wine (verified main source of Resv) differs greatly in the population and the content of Resv varies (mean 1.961.7 mg/L) [20], but the dose may be up to 4 mg/person/day. Only a single experiment has tested Resv in a classical chronic exposure experiments, i.e. at least 24 months in rats or 18 months in mice [21] and Resv does not in general cause any toxic effects in animal studies published except at doses above 1 g/kg bw/day. Besides acute exposure to Resv, several sub chronic experiments have indicated low toxicity. In male Sprague-Dawley rats, 20 mg Resv/kg bw/day given for 28 days did not indicate systemic toxicity [22]. Oral doses of 300, 1000 or 3000 mg Resv/kg bw/day for 28 days only showed toxic effects in the 3000 mg treatment group (CD rats, both sexes) [23], where nephropathy and renal toxicity were observed as well as changed clinical markers of liver metabolism. Exposure of Wistar rats to Resv (50, 150 or 500 mg/kg bw/day) for four weeks or three months to 120, 300 or 700 mg/kg bw/day did not show significant toxicological effects [24]. An additional study of 28 days in rats is mentioned by Elliott et al., which showed ‘‘a no effect level’’ at 300 mg/kg bw/day [16] but no experimental details were given and the results could not be fully evaluated. CD rats (both sexes) exposed to 0, 300, 1000 or 3000 mg Resv/kg bw/day by gavages for 28 days showed only mild liver toxicity as well as nephrotoxicity when exposed to the highest dose [25]. In a study, where female Sprague-Dawley rats were exposed to Resv (1 g/kg diet, corresponding to about 100 mg/kg bw/day in an adult), for the entirety of their life starting at birth showed no toxicological signs such as reduced food intake, reduced body weight, or delayed sexual maturation [26]. In mice (C57BL/6 p532/2) oral administration of Resv (1000, 2000, 3000, 4000 or 5000 mg/kg bw/day) showed an increased death rate caused by impaction of Resv in the gastrointestinal tract Recommendations on the Use of Resveratrol [27]. Long term administration of Resv in drinking water (14 mg/ L water) to mice for six months cause a reduced organ weight but these differences were not present in a corresponding 12 month experiment [28]. Elliott et al [16] cites a study of Resv exposure to rabbits: Severe toxicity was observed at high doses with the kidney as the primary target. The ‘no effect level’ was estimated at 500 mg/kg bw/day in males and 250 mg/kg bw/day in females [16], but no further details were given in the paper. Likewise, Elliott et al. cites a study on the effect of Resv in dogs for 28 days, which showed no toxic effects at 300 mg Resv/kg bw/day, but no details were given [16]. Several experiments have shown that Resv does not have genotoxic activity, based on the Ames test [16,24], but experimental details are too limited to evaluate the data fully. Supporting this, there was no increase in the frequency of micronucleated immature erythrocytes observed in rats exposed to up to 200 mg Resv/kg bw/day [24]. Reproductive toxicity was evaluated in rats and the maternal ‘no observed adverse effect level’ (NOAEL) was estimated at 300 mg/kg bw/day and the developmental NOAEL was estimated at 300 mg/kg bw/day, but no experimental details were given [16]. A study described by Williams et al, indicated that the NOAEL for maternal toxicity and embryo–fetal development was around 750 mg Resv/kg bw/day [24]. Based on these observations, the paper concluded that a daily dose of 450 mg was safe for a 60 kg person, using a 10 fold safety factor [24] which is further the basis of the self affirmed GRAS (Generally Recognized As Safe) status up to 450 mg Resv/day from several Resv producers. Several examples of self reported side effects of Resv intake may be found on various homepages from the internet, but there is no comprehensive evaluation of these self reported side effects. Based on the available data, which mostly originate from studies of very short duration, the working group formulated the following conclusions (Table 2): N There are no valid data on the toxicity of chronic intake of resveratrol in human subjects. N A short term human study (29 days) indicated frequent gastrointestinal discomfort/diarrhea only at high doses (2.5 g or 5 g per day). Only minor and inconsistent side effects have been observed in other short-term or acute studies. What is the relevant dose of resveratrol? Resveratrol has been proposed to be active in the prevention of various life style diseases such as cancer, coronary heart diseases and type 2 diabetes. Different mechanisms are likely involved besides the modulation of inflammation as a unifying mechanism. Because of different mechanisms and targets one must assume that the optimal dose will depend on the particular disease. As indicated above, only a few human studies have been performed, showing down-regulation of cancer biomarkers by 2.5 g Resv/day for 28 days [2] and reduced cell proliferation in colon cancer tissue was observed in humans at doses of 0.5 and 1.0 g Resv/day [3]. A single double-blind, randomized cross-over human study focused on the effect of Resv on flow-mediated dilatation of the brachial artery (as a biomarker of reduced endothelial function and cardiovascular health) in overweight/obese men and women: Resv, at sub chronic doses of 30, 90 and 270 mg/day for one week, showed a significant dose-dependent increase in flow-mediated dilation, significant even at the 30 mg dose [19]. Several human studies have investigated the effects of Resv containing food items. The exposure to Resv is likely in all cases PLoS ONE | www.plosone.org 5 June 2011 | Volume 6 | Issue 6 | e19881