The benefits are linked to lutein in the avocado. Both the eye and the brain selectively incorporate the carotenoid, and new data published in Nutrients showed that daily avocado consumption for six months raised lutein levels in plasma and in the macular in the eye, which is a biomarker for lutein levels in the brain.
Scientists from the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University also found that the increase in macular pigment density (MPD) was related to improvements in working memory and problem solving.
“This study is an example of how practical dietary choices can be of benefit to healthy aging,” they wrote. “A dietary intervention with avocados was particularly effective in increasing MPD levels, a biomarker of brain lutein. Increases in MPD were related to better cognitive performance. Therefore, avocados could be an effective dietary strategy for cognitive health in the aging population.”
Lutein and brain health
The link between lutein and eye health was first reported in 1994 by Dr Johanna Seddon and her co-workers at Harvard University, who found a link between the intake of carotenoid-rich food, particularly dark green leafy vegetables like spinach, and a significant reduction in age-related macular degeneration (AMD) (JAMA, Vol. 272, pp. 1413-1420).
Numerous studies with data from primates, children, middle-aged people, and the elderly now support the importance of lutein in brain health.
Indeed, recent findings from pediatric brain tissue studies have shown that about 60% of the total carotenoids in the pediatric brain tissue is lutein, and yet NHANES data show that lutein is only about 12% of the carotenoids in the diets, so there is a preference for lutein in the brain (Vishwanathan et al. J Pediatr Gastroenterol Nutr. 2014).
The new a six-month, randomized, controlled trial included 20 healthy men and women and randomly assigned them to consume one avocado or one potato/cup of chickpeas per day for six months. An avocado provides a daily lutein dose of about 0.5 mg.
After six months, serum lutein levels in avocado group had significantly increased by 25%, compared to a 15% increase in the potato/chickpea-control group. However, only participants in the avocado group experienced significant increases in MPD after six months.
Cognitive improvements were improved in both groups for memory and spatial working memory, which the researchers suggested may be due to a learning error (increasing familiarity with the tests). Only the avocado group displayed significant improvements in sustained attention.
The researchers also found that the MPD increase observed in the avocado group was correlated with improvements in both working memory and the efficiency in approaching a problem.
“A dietary intervention with avocados was found to improve cognitive function,” they wrote. “This improvement could be related to the increase in MPD, a biomarker of lutein contained in brain tissue. The proposed mechanisms by which lutein benefits cognitive function in the elderly may involve its role as an antioxidant or anti-inflammatory agent. However, in this study, no changes in oxidative stress or inflammation biomarkers were detected in either group. These measures were within a normal range at the start of the study, and therefore an improved antioxidant for anti-inflammatory status would have been difficult to detect.
“Other proposed mechanisms by which lutein is embedded in neural tissue include the modulation of functional properties of synaptic membranes, along with certain changes in the physiochemical and structural features of these membranes.”
Supplement formulation lessons?
The Tufts University team have previously performed studies with dietary supplements containing 12 mg lutein and 0.5 mg of zeaxanthin per day, with four months of supplementation associated with significant increases in MPD.
Avocados provided a lower daily lutein dose (0.5 mg) but more than doubled the MPD compared to the supplement.
“This suggests that other components in avocado are particularly effective in the enrichment of neural lutein. The most likely components are monounsaturated fatty acids,” they wrote.
2017, Volume 9, Issue 9, Page 919; doi:10.3390/nu9090919
“Avocado Consumption Increases Macular Pigment Density in Older Adults: A Randomized, Controlled Trial”
Authors: T.M. Scott, et al.