Written by Greg Arnold, DC, CSCS. Participating subjects who ate one avocado a day for six months had significant increases in lutein levels, improved Short-Term Visual Memory and Sustained Attention scores as well as improved MPD, an indicator of improved cognitive function.
Lutein and zeaxanthin, two dietary carotenoids crucial to long-term eye health, cross the blood brain barrier and accumulate exclusively in the retinal macula. (1) Collectively known as macular pigment (MP), macula, lutein and zeaxanthin filter blue light that can damage the retina. (2)
Previous research has shown macula pigment density to be significantly related to cognitive function in both young and older adults (3, 4). In addition, lutein concentrations in the older adult brain are positively associated with a variety of pre-mortem cognitive measures (5), thus macula pigment density has become a non-invasive biomarker for brain concentrations of lutein.
Based on previous research on lutein’s ability to significantly influence verbal fluency in older adults, researchers investigated the ability of lutein-rich avocados to improve MPD. (7) In a 2017 randomized placebo -controlled study , forty-eight men and women between the ages of 52 and 74, consumed either one avocado weighing approximately 135 grams and containing 0.5 milligrams of lutein (n=20 subjects) or a placebo consisting of one potato or one cup of chickpeas and no lutein (n = 20 subjects) for six months. The researchers chose avocados as they are high in absorbable lutein (8) while other sources of lutein include green leafy vegetables, squash, broccoli, and eggs (9). Blood samples were taken before and after the study as well as midway through the study (3 months) to measure for lutein levels as well as macula pigment density. Each subject completed a series of cognitive tests (10) to measure overall cognitive function.
- The researchers noted statistically significant increases in lutein levels in the avocado group at 6 months (25.4% increase (330 to 414 nanomoles/liter), p = 0.001) and 28.2% at 3 months (330 to 423 nmol/L, p = 0.001) compared to a statistically significant increase in the control group at 6 months (322 to 371 nmol/L, p = 0.03).
- For the cognitive tests, those in the avocado group showed a statistically significant improvement in Short-Term Visual Memory (p = 0.020) and in Sustained Attention (p = 0.033) while no statistical significance was reached in the placebo group (p > 0.05). The avocado group also reached significance while significance not reached by the control group in either cognitive measure (p > 0.05).
- In the avocado group, the change in MPD was significantly related to changes in Spatial Working Memory (r = 0.46, p = 0.041) and the efficiency in approaching a problem (r = 0.47, p = 0.036). There were no relationships between the change in MPD and the change in cognition in the control group.
“This study is an example of how practical dietary choices can be of benefit to healthy aging”. Dietary intervention with avocados was particularly effective in increasing levels of MPD, a biomarker of brain lutein and indicator of improved cognitive performance. Therefore, avocados could be an effective dietary strategy for cognitive health in the aging population.
Source: Scott, Tammy M., Helen M. Rasmussen, Oliver Chen, and Elizabeth J. Johnson. “Avocado Consumption Increases Macular Pigment Density in Older Adults: A Randomized, Controlled Trial.” Nutrients 9, no. 9 (2017): 919.
© 2017 by the authors. Licensee MDPI, Basel, Switzerland. Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/)
Click here to read the full text study.
Posted October 30, 2017.
References:
- Bone, R.A.; Landrum, J.T.; Tarsis, S.L. Preliminary identification of the human macular pigment. Vis. Res. 1985, 25, 1531–1535
- Johnson, E.J. A role for lutein and zeaxanthin in visual and cognitive function throughout the lifespan. Nutr. Rev. 2014, 72, 605–612.
- Feeney, J.; Finucane, C.; Savva, G.M.; Cronin, H.; Beatty, S.; Nolan, J.M.; Kenny, R.A. Low macular pigment optical density is associated with lower cognitive performance in a large, population-based sample of older adults. Neurobiol. Aging 2013, 34, 2449–2456
- Renzi, L.M.; Dengler, M.J.; Puente, A.; Miller, L.S.; Hammond, B.R. Relationships between macular pigment optical density and cognitive function in unimpaired and mildly cognitively impaired older adults. Neurobiol. Aging 2014, 35, 1695–1699
- Johnson, E.J.; Vishwanathan, R.; Johnson, M.A.; Hausman, D.B.; Davey, A.; Scott, T.M.; Green, R.C.; Miller, L.S.; Gearing, M.; Woodard, J.; et al. Relationship between serum and brain carotenoids, alpha-tocopherol, and retinol concentrations and cognitive performance in the oldest old from the Georgia Centenarian Study. J. Aging Res. 2013
- Johnson, E.J.; McDonald, K.; Caldarella, S.M.; Chung, H.-Y.; Troen, A.M.; Snodderly, D.M. Cognitive findings of an exploratory trial of docosahexaenoic acid and lutein supplementation in older women. Nutr. Neurosci. 2008, 11, 75–83
- Scott TM. Avocado Consumption Increases Macular Pigment Density in Older Adults: A Randomized, Controlled Trial. Nutrients 2017 Aug 23;9(9). pii: E919. doi: 10.3390/nu9090919
- Unlu, N.Z.; Bohn, T.; Clinton, S.K.; Schwartz, S.J. Carotenoid absorption from salad and salsa by humans is enhanced by the addition of avocado or avocado oil. J. Nutr. 2005, 135, 431–436.
- Perry, A.; Rasmussen, H.; Johnson, E.J. Xanthophyll (lutein, zeaxanthin) content in fruits, vegetables and corn and egg products. J. Food Compos. Anal. 2009, 22, 9–15
- Robbins, T.W.; James, M.; Owen, A.M.; Sahakian, B.J.; McInnes, L.; Rabbitt, P. Cambridge Neuropsychological Test Automated Battery (CANTAB): A factor analytic study of a large sample of normal elderly volunteers. Dementia 1994, 5, 266–281
