The elderly represent a group for whom health issues are of paramount concern. Physiological processes, including the functioning of the immune and digestive systems, are known to decline with age, and consequently aging can increase susceptibility to infectious and non-infectious disease. Dietary supplementation may offer a safe and effective means of countering physiological senescence, by optimizing important immune and gut functions. This review outlines our current understanding of the ways in which aging affects immune and gut function, and discusses clinical evidence for a role of dietary supplementation in countering age-related deficiencies in these processes.