Melatonin in walnuts: influence on levels of melatonin and total antioxidant capacity of blood.

OBJECTIVE We investigated whether melatonin is present in walnuts (Juglans regia L.) and, if so, tested whether eating walnuts influences melatonin levels and the total antioxidant status of the blood. METHODS Melatonin was extracted from walnuts and quantified by high-performance liquid chromatography. After feeding walnuts to rats, serum melatonin concentrations were measured using a radioimmunoassay and the "total antioxidant power" of the serum was estimated by using the trolox equivalent antioxidant capacity and ferric-reducing ability of serum methods. RESULTS Mean +/- standard error melatonin concentrations were 3.5 +/- 1.0 ng/g of walnut. After food restriction of rats and then feeding them regular chow or walnuts, blood melatonin concentrations in the animals that ate walnuts were increased over those in the rats fed the control diet. Increases in blood melatonin were also accompanied by increases in trolox equivalent antioxidant capacity and ferric-reducing ability of serum values. CONCLUSIONS Melatonin is present in walnuts and, when eaten, increase blood melatonin concentrations. The increase in blood melatonin levels correlates with an increased antioxidative capacity of this fluid as reflected by augmentation of trolox equivalent antioxidant capacity and ferric-reducing ability of serum values.