Blue light nemesis: Green veggies’ carotenoids

Key nutrients found in leafy, green vegetables help protect against high-energy blue light emitted from digital devices, and a new study suggests supplementing these nutrients may boost their protective quality.

Published in the open-access food science journal Foods, the University of Georgia study concluded that supplementation with macular carotenoids, lutein and zeaxanthin, increased macular pigment optical density (MPOD) and, in turn, improved subjects' headache frequency, eye strain, eye fatigue and other visual performance measures often associated with prolonged digital screen time.

Analyzing results of the 6-month randomized, double-blind, placebo-controlled, Blue Light User Exposure (BLUE) study, researchers examined 48 healthy adults with screen time of at least 6 hours daily, collecting data on their MPODs and other physical indicators. Researchers determined that subjects taking a 24 mg/daily macular carotenoid supplement yielded significant improvements in MPOD versus a placebo group that correlated with positive reporting on the aforementioned physical indicators.

"After six months of supplementation, we saw significant reduction around 30% in these symptoms and significant improvement in measures of visual performance and protection," stated lead author James Stringham, Ph.D., in a news release.

The study concludes that macular carotenoid supplementation may offer a "benign, nutrition-based therapy for reducing the incidence of many undesirable outcomes associated with excessive (screen time)." It also adds that more research into the 40-45 years age group and those younger than 10 is necessary to determine the effects of long-term squinting in pre-clinical presbyopia and the effects of a clear, crystalline lens with little appreciable macular pigmentation, respectively.

Understanding nutrition and blue light

Although the ocular benefits of lutein and zeaxanthin on MPOD have been known for some time, these new findings add to researchers' understanding of how supplementation can affect physical indicators of excessive screen time usage, such as eye strain, fatigue, headaches and even sleep quality. The Age-Related Eye Disease Study (AREDS) and AREDS 2 determined nutrition could play a significant role in eye health, and concluded that lutein and zeaxanthin had a role in protecting against high-energy blue and ultraviolet (UV) light.

Of the 600 carotenoids found in nature, lutein and zeaxanthin are the only two deposited in high quantities in the eye's macula. Importantly, these antioxidants—commonly found in kale, collard greens and spinach—eliminate the free radicals produced by high-energy blue light exposure on the retina, and help absorb that damaging light.

Susan Summerton, O.D., a certified nutrition specialist with the Ocular Nutrition Society, explains this filtering effect is due to coloration—macular pigment is yellow due to the presence of lutein and zeaxanthin, and that allows it to attenuate blue light.

She explains that the xanthophylls (yellow pigments) can protect by absorbing the ionizing blue light and limit the excitation in the retina. This protects the vitamin A cycle in the eye that is required for photoreceptor regeneration of opsins. Lutein and zeaxanthin, therefore, protect melanopsin in the central retina—a photopigment key to non-image-forming pathways—which drives the "eye clock" for circadian rhythms.

"When the vitamin A cycle is off, you have a circadian mismatch. We end up using more carotenoids with chronic exposure to blue light," Dr. Summerton explains.

"Blue light alters the central retinal hypothalamic pathways to ruin how the eye clock mechanism works."

In other words, that's why blue light exposure at nighttime is correlated with wakefulness and a delayed or poor sleep cycle. Blue light, in the 420-480 nm wavelength spectrum, affects the levels of the sleep-inducing melatonin, disrupting the body's natural circadian rhythm.

Read more about blue light exposure and eye health in the March 2014 edition of AOA Focus.