Eating a diet full of lutein-rich foods, such as kale and spinach, in middle age may guard against age-related cognitive impairment, new research suggests.
In a study of 60 adults aged 25 to 65 years, investigators assessed levels of lutein – a nutrient that accumulates in both brain and eye tissue – using macular pigment optical density (MPOD).
Results showed that higher vs lower levels of lutein were associated with significantly greater attentional inhibition.
In addition, neural responses in the older participants who had high lutein levels/MPOD scores were similar to those in the younger participants.
“This study reiterates the importance of a healthy diet across the life span,” lead author Anne M. Walk, PhD, Department of Kinesiology and Community Health, University of Illinois at Urbana-Champaign, told Medscape Medical News.
“Previous research has shown that eating lutein-rich foods such as leafy green vegetables, eggs, and avocados has health benefits for individuals. Our work suggests that the benefits of a healthy diet may extend beyond physical health and improve cognitive processing as well,” said Dr Walk.
She added that the nutrient also appears to play a protective role, because participants with greater lutein levels “were able to engage more cognitive resources to complete their tasks.”
The findings were published online June 9 in Frontiers in Aging Neuroscience.
Optimal Cognitive Processing
In previously published research, the investigators found that for children with higher levels of lutein and zeaxanthin, scores on tests of academic performance were higher than for their peers with lower levels of these retinal carotenoids.
In addition, Dr Walk noted that a lot of previous research has focused on the link between lutein intake and optimal cognitive processing in older adults.
“Although most people tend to think of aging as something that happens in older adulthood, there is some research that shows that cognitive decline can actually begin earlier in the life span,” she said.
“We wanted to explore the possibility that lutein may be protective against cognitive aging not only in older adults or in those who may already be showing signs of decline but in middle age, closer to the time in life where decline may begin.”
The researchers enrolled 60 participants aged 25 to 45 years (mean age, 33.8 years; 52% women) and who lived in a single region of Illinois. A macular densitometer was used to measure MPOD.
A randomized, two-stimulus “oddball” task measured selective attention; the Eriksen flanker test measured attentional inhibition; and the go/no-go task measured response inhibition.
A Neuroscan Quik-cap was used to record EEG activity during the tasks in order to provide event-related potential (ERP) analysis. “The ERP variables of interest for all tasks were the peak amplitude and peak latency at the PZ electrode, where P3 is maximal in typical healthy adults,” the investigators note.
Younger Brains
On the oddball task, age was inversely associated with accuracy of response to frequent/standard stimuli, meaning scores were higher for those who were younger (P = .04). MPOD was associated with increased reaction time (P = .004) and “inverse efficiency to target stimuli” (P = .047).
The latter finding suggests that the participants with high MPOD scores “likely adopted a response set strategy in which they responded more slowly” than those with lower MPOD scores, note the investigators.
On the other hand, flanker test results showed that the participants with higher MPOD scores were significantly more likely to efficiently process information on incongruent trials than those with lower scores (P < .02), suggesting that this effect may depend on tasks with high attentional-inhibition demands.
ERP data showed that those whose MPOD values were higher, amplitudes during incongruent flanker trials were larger (P = .045).
In addition, “the neuro-electrical signature of older participants with higher levels of lutein looked much more like their younger counterparts than their peers with less lutein,” said Dr Walk in a release.
Several performance indexes showed that age itself was linked to less efficient cognitive processing. However, hierarchical linear regression analyses showed that when MPOD was added as a model variable, neither age nor MPOD significantly predicted peak amplitude, “suggesting that the relationship between age and PZ peak amplitude is at least partially accounted for by MPOD,” the researchers note.
There were no significant associations between the factors and go/no-go response-inhibition results.
Selective Benefits
Overall, “the benefits of greater retinal carotenoids appeared to be selective for intraindividual variability and attentional resource allocation during the flanker task, rather than in the oddball or the go-nogo tasks,” write the investigators.
“Since previous research has established an association between lutein found in the eye and cognitive abilities in older adults, it is not entirely surprising to see a similar effect in middle-aged adults,” Dr Walk said.
“However, it is important to establish this link in middle-aged and younger adults so that we can get closer to discovering optimal recommendations for lutein intake across the life span.”
Dr Walk added that taken together, old research, this study, and the investigators’ previous study on lutein and school performance show that carotenoids seem to be beneficial in all age groups.
“While the extent of the effects of lutein for people in various developmental stages needs to be established in further research, our studies suggest that it is important for both children and adults if they want to maintain optimal cognitive processing abilities.”
Coinvestigator Naiman A. Khan, PhD, professor of kinesiology and community health, who is also at the University of Illinois, reported in the release that the investigators are now working on intervention trials.
Although this study focused on attention, “we also would like to understand the effects of lutein on learning and memory. There’s a lot we are very curious about,” said Dr Khan.
“Compelling Data”
Commenting on the findings for Medscape Medical News, Elizabeth Johnson, PhD, Nutrition Research Center on Aging at Tufts University, Boston, Massachusetts, noted that research on a link between lutein and cognitive function “is relatively new,” having first been described in 2008.
Dr Elizabeth Johnson
“It’s only been about a decade, but since then the data are accumulating and fairly consistent. And what I like is that different laboratories are finding the same thing using different methods, different populations, and different age groups,” said Dr Johnson.
Although the current study used cross-sectional data to suggest an association, “the interventional trials with lutein have happened,” she said.
“So I believe there’s a lot of compelling data telling us that lutein is important for cognitive function. And certainly the clinical data, the epidemiology, and the observational data all point to the same thing: that it’s important through the life span.”
Dr Johnson and colleagues have previously measured carotenoid levels in infants who died. She noted that their findings suggest lutein might also be important in neurodevelopment.
They are now working on mechanistic studies of lutein in the brain and hope to present their results soon.
When asked if she was at all bothered by the fact that the current study was funded in part by an avocado organization, Dr Johnson said no. “I think these boards should know more about their product and if there are risks or benefits to it. They should be interested in the science behind components that are contained in their product.”
However, she added that “it would have been nice” if the investigators had assessed the participants’ specific diet intake.
The study was funded by the University of Illinois and by the Hass Avocado Board. Dr Walk and the other study authors have reported no relevant financial relationships. Dr Johnson reported that she “does lutein research on cognitive function” and receives funding from the Center for Nutrition Learning and Memory. She has in the past coauthored articles with some of the investigators on the current study.
Front Aging Neurosci. Published online June 9, 2017. Full article
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