According to an evidence-based review, antioxidants help to protect from certain chronic diseases of aging, including cardiovascular, neurological and anticarcinogenic ailments due to their ability to control free radicals - known to negatively influence healthy aging. Walnuts contain many antioxidants (13.126 mmol/gram). In a 2006 study, 1113 different foods were tested and walnuts ranked second only to blackberries in terms of antioxidant content (see graph below).
Another study examining the levels of antioxidants in various foods, reported at least 10 different antioxidants present in walnuts (802 mg GAE of total phenols per ounce). According to the study, a handful of walnuts has significantly more phenols (an antioxidant) than a glass of apple juice (117 mg), a milk chocolate bar (205 mg), or a glass of red wine (372 mg).
Melatonin is an antioxidant that is naturally found in walnuts. Research, led by melatonin expert Dr. Russel Reiter, published in the September 2005 issue of Nutrition: The International Journal of Applied and Basic Nutritional Sciences, reported the calculated concentrations of melatonin in walnuts was 3.5 +/- 1.0ng/g.