One of the most widely accepted theories proposed to explain ageing is the free radical theory, according to which oxygen-derived free radicals cause age-related impairment through oxidative damage to biomolecules, with mitochondria being the main target of free radical attack. Since oxygen radicals are needed for many metabolic and physiological processes, an equilibrium between radical production and their antioxidant-linked inactivation is required to preserve health. Thus, senescence is the result of an imbalance between free radical production and antioxidant defences, with concomitant oxidative stress and age-dependent functional decline. This process is especially evident in the immune cells, which use free radicals in their functions and suffer a senescent deterioration probably linked to oxygen stress. Conversely, several laboratories, including our own, have shown that antioxidants preserve an adequate function of immune cells against homeostatic disturbances caused by oxidative stress, such as that involved with age. Therefore, since the immune system is an indicator of health and a longevity predictor, the protection of this system afforded by dietary antioxidant supplementation may play an important role in order to achieve a healthy ageing.