Greater focus has been placed on gaining a better understanding of what factors may be accelerating cognitive decline when trying to extend cognitive functioning into old age and reducing the costs of care later in life. Oxidative stress is one of those factors coming to the forefront as this is an imbalance in the favor of pro-oxidant metabolism and the stress of which may contribute to neurodegenerative diseases and other age-related conditions.
Our brains may be particularly vulnerable to reactive oxygen species that accumulate due to DNA repair impairment that occurs with age, because of this it accounts for 20% of all bodily oxygen consumption, thus exposure can trigger an unfavorable DNA oxidative modification within the brain.
Oxidative stress is an imbalance caused by excessive ROS over the capability of the cell to mount an effective antioxidant response. Studies have shown that dietary intake of antioxidants have helped to reduce lipid peroxidation, production of ROS, apoptosis, as well as protein and DNA oxidative damage. Studies also suggest that dietary intake of antioxidants, supplements, and serum may play a neuroprotective role. Evidence also suggests that there is a biological synergism between some carotenoids and other antioxidants; increased intake of carotenoid B-carotene may reduce blood levels of vitamin E.
It was hypothesized that dietary antioxidants could slow the pace of cognitive decline among middle-aged adults to delay the onset of Alzheimer’s disease and other forms of dementia later in life. Additionally, the researchers also wanted to uncover any synergism between antioxidants. To test their hypothesis the team used longitudinal data from a large biracial study of urban middle-aged adults to examine the adjusted association among several dietary antioxidants and cognitive performance change over time, specifically vitamins A, C, E and carotenoids including a-carotene, B-carotene, lutein + zeaxanthin, B-cryptoxanthin, and lycopene.
The initial Cohort of HANDLS involved 3720 participants between the ages of 30-65 who underwent fasting blood draw, complete physical exams, dual-energy X-ray absorptiometry scans, electrocardiograms, cognitive assessment, and a second 24-hour dietary recall. The first follow up visit was estimated at 4.66 years and consisted primarily of an MRV in-depth exam visit that assessed cognitive performance in a similar manner as the first visit.
The team reported consistent synergism between total and individual carotenoids and vitamin E in relation to baseline cognitive performance in verbal memory, verbal fluency, attention, working memory, and executive functions.
Vitamin E was reported to be associated with greater verbal memory performance in the uppermost tertile of carotenoids, and the association was largely driven by lycopene intake. Vitamin A was associated with a faster decline on a test of visual memory and visuo-constructive ability within the uppermost tertile of total carotenoids, and this association was largely driven by B-carotene and lutein + zeaxanthin. Vitamins A and C showed inconsistent interactions with carotenoids with respect to baseline cognitive performance and change in test scores over time.
There was no antagonism found between B-carotene and vitamin E, but there was some evidence of synergism between a-carotene and vitamin E in relation to performance in multiple domains of cognition.
The team concluded that “The clinical interpretation and implications of this study are that a diet rich in vitamin E and carotenoids, including lycopene, may reduce the likelihood of cognitive decrements in the short term, particularly in the domain of verbal memory.“
“Time-dependent changes in dietary and plasma levels of antioxidants need to be linked with changes in cognitive performance over time in future cohort studies, in a lagged manner, to ensure temporality of the associations and to incorporate supplemental sources of antioxidants. Pending such studies, randomized trials examining synergism between carotenoid and vitamin E in relation to cognitive performance and decline are needed.”
It was noted that within the total population and after correction for multiple testing that there was limited evidence of an association between each of these antioxidants and cognitive performance or decline.
