Carotenoids are a natural plant chemical that can be found in a variety of vegetables and fruits, such as carrots, pumpkins, peppers, tomatoes, potatoes, and oranges.

However, some carotenoids, like lutein (L) and zeaxanthin (Z) can also be found in dark green vegetables such as kale, spinach, and peas.

A variety of studies have shown that diets rich in L and Z help maintain visual health, improve visual acuity, and slow down some age-related eye diseases.

Other studies have suggested L and Z improve cognitive function in adults aged 98 years and over. Increased levels of the compounds were associated with better memory and higher verbal fluency.

However, the neural mechanisms responsible for the association between carotenoids and cognition remains unknown.

In an attempt to untangle these mechanisms, new research looks at carotenoid levels and brain activity in elderly adults.
Studying link between carotenoids and cognition in elderly adults

Researchers asked 43 community-dwelling adults aged between 65-86 years to learn and remember pairs of unrelated words while undergoing brain imaging through functional magnetic resonance imaging (fMRI).

All participants were white, and 58 percent of them were women.

Scientists assessed the levels of L and Z in the retina by measuring the macular pigment optical density.

The team was led by Cutter Lindbergh, a doctoral candidate in the psychology department of the Franklin College of Arts and Sciences at the University of Georgia.

The results were published in the Journal of the International Neuropsychological Society.
L and Z improve neural efficiency

Scientists found that higher levels of L and Z correlated with a lower signal in several areas of the brain, as measured by the level of oxygen in the participants' blood.

This indicated lower brain activity in individuals with higher levels of L and Z during memory tasks, which means they did not have to work as hard to complete the task.

The results therefore suggest that L and Z promote cognitive functioning in old age by improving neural efficiency.

    "There's a natural deterioration process that occurs in the brain as people age, but the brain is great at compensating for that. One way it compensates is by calling on more brain power to get a job done so it can maintain the same level of cognitive performance. On the surface, it looked like everyone was doing the same thing and recalling the same words, but when you pop the hood and look at what's actually going on in the brain, there are significant differences related to their carotenoid levels."

    Cutter Lindbergh

The study found no correlation between how many words participants could recall and the levels of carotenoids.
Study findings reflect need to improve dietary habits

This is the first time a study investigates the relation between L and Z to cognitive function using fMRI technology.

The findings showed how the brain compensates for the decline in cognition that comes with age. The lead researcher of the study emphasizes the need to change our dietary habits in light of the new findings.

"It's in the interest of society to look at ways to buffer these decline processes to prolong functional independence in older adults," Lindbergh says. "Changing diets or adding supplements to increase lutein and zeaxanthin levels might be one strategy to help with that."

In the future, researchers hope to be able to examine whether dietary interventions such as changes in nutrition to include more carotenoid-containing vegetables, or the intake of dietary supplements, could improve individuals' cognitive power.

"If you can show that in fact there's a real mechanism behind this, then you could potentially use these nutritional supplements or changes in diet, and you could easily intervene and potentially improve cognition in older adults," says L. Stephen Miller, a professor of psychology and corresponding author of the study.