Lutein is also preferentially taken up by brain tissue and is the carotenoid most consistently related to cognitive function.
The cognitive effect of consuming lutein-containing foods, however, has not been explored.
Given that avocados provide a highly bioavailable source of lutein, researchers at Tufts University conducted a randomised controlled trial to test the effect of avocado consumption on cognition in older adults.
A total of 48 healthy adults (mean age = 63 years) were randomised to eat one fresh avocado (intervention) or an isocaloric amount of potatoes and chickpeas (control) per day for 6 months.
Hass Avocados were sourced from Mission Viejo (CA, USA) and provided approximately 0.5 mg of lutein per medium avocado per day. Potatoes from Costa Produce and chickpeas from Progresso provided no lutein.
The subjects performed a battery of computerised cognitive tests at baseline, 3 months and 6 months. There were no significant differences in cognitive function between the intervention and control group at baseline.
There were significant improvements in the avocado group in spatial working memory at 3 months and in the Stockings of Cambridge test (which measures total thinking time and problems solved in minimum moves) at 6 months. There were no significant changes in cognitive measures in the control group.
In addition to improved cognitive function, the avocado group experienced a 25% increase in serum lutein concentrations and a 25% increase in macular pigment density (a biomarker of brain lutein) at 3 months, both of which persisted until 6 months.
The control group experienced a 15% increase in serum lutein at 6 months and a slight increase in macular pigment density at 3 months that did not persist at 6 months.
A comparison of this study with a similar study of lutein supplementation puts the results into perspective.
A previous clinical trial provided 12 mg per day of lutein supplement for 4 months to older adults. The current study provided 0.5 mg per day of lutein in the form of an avocado.
The avocado intervention increased macular pigment density by more than twice as much as the supplement (0.041 optical density for the supplement and 0.101 for the avocado). This suggests that avocados provide a synergy of compounds that work better than lutein alone to enrich neural lutein.
The authors of the current study conclude that avocado consumption may be an effective way to increase macular pigment density and improve cognitive performance in older adults.