In the news: Carotenoids & Visual Processing, Carotenoids in Early AMD

Carotenoids and Neural Processing Speed

Aging is often accompanied by a decline in central nervous system efficiency that tends to manifest as deficits in such functions as short-term memory and decision-making ability, as well as more basic functions such as reaction time. A slowing of processing speed appears to be central to these declines, is an important marker of optimal brain function, and may predict future cognitive decline.

One potential approach to improving neural processing and influencing brain function is to provide dietary components that reflect neural tissue composition. Over half the brain is fat, for example, and the brain tends to preferentially accumulate fluid fats like DHA over more rigid saturated fats.

Lutein and zeaxanthin are also components of the nervous system. It has been hypothesized that these carotenoids influence the processing of visual signals within and beyond the retina, and that increasing lutein and zeaxanthin levels in the visual system will lead to improved processing speeds.

To test that hypothesis, University of Georgia researchers measured macular pigment optical density (MPOD), visual motor reaction time, and critical flicker fusion (CFF) in 64 young healthy adults randomly assigned to receive a combination of lutein, zeaxanthin and omega-3 fatty acids, or zeaxanthin alone, or placebo for 4 months (1).

At baseline, significant correlations were found between MPOD and CFF thresholds and visual motor performance. The supplement groups (combined to increase statistical power) showed significant increases of about 12% in CFF thresholds and about 10% in visual motor reaction time compared to placebo. Average MPOD increased (about 0.09 log units) with supplementation.

This line of research is relatively new, and more and larger studies are needed to determine whether modifying neural levels of these carotenoids actually improves processing speeds and cognitive function. So far, one small placebo-controlled trial has found

that supplemental DHA, lutein and zeaxanthin improves cognitive function in elderly women. In studies with monkeys, measuring MPOD has been shown to be a good proxy for the amount of lutein and zeaxanthin in the brain. Further, CFF has been associated with cognitive performance. Taken together, this suggests that lutein and zeaxanthin may influence neural processing speed in both the brain and the eye.

Carotenoids & Neural Sensitivity in Early AMD

Some AMD intervention studies report that supple-mentation with macular carotenoids increases MPOD and improves visual function, while others have found no significant improvements in visual function despite increases in MPOD. That may be because structural changes do not affect retinal function in earlier stages of the disease, or because visual measurements have not been sensitive enough to detect visual benefits.

To shed light on this question, researchers randomly assigned 112 patients with early AMD to receive 10 mg lutein, 20 mg lutein, lutein and zeaxanthin (10 mg each) or placebo for 2 years (2). Retinal sensitivities were measured by multifocal electroretinogram (N1P1) and in terms of micro-perimeter-determined mean retinal sensitivity (MRS).

Carotenoid supplementation in all active treatment groups significantly increased MPOD. N1P1 response densities increased in rings 1 and 2 (though not rings 3-6) in all active treatment groups. Increases in MRS were seen with either 10 mg or 20 mg lutein, while no increases were seen in the placebo arm.

This study shows that MPOD can be augmented and visual function enhanced with supplemental macular carotenoids. The fact that gains in MPOD were similar between 10 and 20 mg lutein doses at 2 years reinforces the idea that incorporation of macular carotenoids in the retina is a saturable process.

References

1. Bovier ER, et al. A double-blind, placebo-controlled study on the effects of lutein and zeaxanthin on neural processing speed and efficiency. Plos One 9:e108178, Sept, 2014.
2. Huang Y-M, et al. Changes following supple-mentation with lutein and zeaxanthin in retinal function in eyes with early age-related macular degeneration: a randomized, double-blind, placebo-controlled trial. Br J Ophthalmol Online first: Sept 16, 2014.