ABSTRACT
An important goal of aging research is to identify interventions that will result in the preservation of cognitive function throughout the life span of an individual. This goal is becoming more critical as our population ages, particularly because there are a rising number of individuals affected by Alzheimer’s disease (AD), one of the most common causes of dementia in the elderly. Age is the biggest risk factor for the development of AD. This suggests that neurobiological changes associated with aging may leave the brain vulnerable to AD-associated neurodegeneration. The brain consumes 20% of the body’s oxygen, which results in the normal production of free radicals that can damage lipids, proteins, and nucleotides.1 Neurons are nondividing and are vulnerable to cumulative oxidative damage.2 One of the primary sources of free radicals within neurons is from mitochondria, which become less efficient with age, leading to increased oxidative
damage.1,3,4 These observations have led to the hypothesis that a diet rich in antioxidants (e.g., vitamins E and C), the use of antioxidant supplements, and dietary enrichment with mitochondrial cofactors (e.g., lipoic acid, carnitine) may be protective against AD and promote successful aging.3,5,6
In human observational studies, a positive effect of antioxidant supplementation on cognition7-13 in the elderly has been reported. Further, antioxidant supplement use also reduces the risk of developing AD and slows cognitive decline associated with AD.10,14-17 Supplementation with the use of single antioxidants such as vitamins E or C alone may have more limited effectiveness than a combination of antioxidants on cognition or risk of development of AD.7,13,16 Moreover, intake of antioxidants through food (e.g., dietary phytochemicals18) may be superior to supplements (i.e., pills) in human studies (i.e., tablets).10 However, not all study outcomes have been positive; several studies report a lack of significant beneficial effects of antioxidant supplements on cognition or the development of AD.19-21 Differential outcomes in observational studies may reflect sample biases. For example, women more frequently take supplements than men, and more highly educated individuals more often take supplements. There is also the possibility that antioxidants obtained through daily diet may exceed those obtained through supplements and are not included in calculations of antioxidant intake. Outcomes of different epidemiological studies may also depend on critical factors such as the type of population being studied, and the validity and clinical relevance of the outcome parameters.
