The effect of a mangosteen product containing multivitamins and essential minerals was tested on immune function and well-being in healthy adults. A randomized, double blinded, placebo-controlled study was conducted in 59 healthy human subjects (40-60 years old). Changes from baseline immune function were measured after a 30-day consumption of the mangosteen product and the placebo. The subjects' self-appraisal of their health status was also surveyed. A xanthone-rich mangosteen product intake increased mean values for peripheral T-helper cell frequency (P = .020) and reduced the serum C-reactive protein concentration (P = .014). Increases in peripheral CD4/CD8 double-positive (DP) T-cell frequency and serum complement C3, C4, and interleukin (IL)-1alpha concentrations were significantly higher in the experimental group than in the placebo group (DP, P = .038; C3, P = .017; C4, P = .031; IL-1alpha, P = .006). At the end of study, serum IL-1alpha and IL-1beta concentrations in the study group were significantly higher than that in the placebo group (IL-1alpha, P = .033; IL-1beta, P = .04). Furthermore, more participants in the experimental group reported greatly improved overall health status compared with participants receiving placebo (P = .001). The results indicated that the intake of an antioxidant-rich product significantly enhanced immune responses and improved the subject's self-appraisal on his or her overall health status.