Lutein and Zeaxanthin (LZ) are powerful carotenoid antioxidants. In the plant kingdom they double as natural yellow pigments, and their important functions include protecting against free radicals generated by intense light and maintaining the structural and functional integrity of cell membranes. Amazingly, they perform these same functions in humans as well![1]
While humans cannot synthesize LZ, their dietary consumption benefits us in many ways, most notably via their maintenance and protection of eyesight.[2][3][4] They support everyday visual function through improved contrast sensitivity[5] and reduced glare.[6] In large-scale clinical trials, LZ supplementation reduces the risk of developing age-related macular degeneration (AMD),[7][8] a disease that is projected to affect the vision of 300 million people by the year 2040.[9]
Humans can store a finite amount of LZ in the skin[10] and liver,[11] the brain preferentially accumulates lutein across multiple life stages,[12][13] and they are passed on to infants through maternal breast milk.[14]
If the above suggests that LZ are vital to human health, you won’t be surprised to learn that there are some who suggest they be reclassified as ‘conditionally essential’ nutrients, such is their importance.[15] Eager to find out more about these unique antioxidants and explore their potential? Let’s go!
Dietary Green and Gold
Despite being yellow pigments, high amounts of LZ are found in green leafy vegetables such as spinach and kale.[16][17] They are also present in yellow egg yolks as a result of corn-based or supplemented poultry feed. Although the levels in eggs are not quite as high as those found in certain vegetables, evidence suggests they are more bioavailable from eggs,[18] due to the presence of fat which enhances their uptake.[19] In addition, the majority of plant sources contain only lutein whilst lacking zeaxanthin, whereas eggs and corn contain both.[20] Interestingly, goji berries contain the highest amounts of zeaxanthin of any food.[21]
Eye See the Light
LZ are vital to eye health. They are the only dietary carotenoids that cross the blood–retina barrier, where they accumulate and form a visible yellow spot called the macula lutea.[22][23][24] The macula is responsible for central vision and visual accuracy – it is here that these carotenoids protect crucial photoreceptor cells from free radicals generated upon exposure to light.[25]
In addition to antioxidant activity, LZ also filter the high-energy wavelengths of blue light.[26][27] See Figure 1. LZ filter the light which bypasses the cornea and lens and enters the back of the eye. Here they mitigate exposure to blue-violet light, protecting against the harmful short wavelength radiation caused by this part of the visible spectrum.[28]
Figure 1. Absorption and transmission of solar radiation in the eye. The cornea and crystalline lens filter out UVB and most UVA, so that the most energetic light reaching the retina is short wavelength blue-violet light.[29]
Blue Light Bedtime Blues
The visible spectrum is comprised of wavelengths of light, and each wavelength is a particular colour. The colour we see is a result of which wavelengths are reflected back to our eyes. See Figure 2 below.
Although sources of blue light are everywhere, before the advent of artificial lighting, our closest star was the one principal source.[30]
Nowadays, artificial sources of blue light are everywhere, and importantly, they are on all the time. Fluorescent lighting, LED TVs, computer, tablet and mobile phone screens impact our eyes at all times of the day and night.
Figure 2. The visible spectrum
While blue light can improve reaction times, attention span, working memory and brain function,[31][32][33] it may also negatively affect sleep. This is because when the sun rises in the morning, our body produces the hormone cortisol, which stimulates and maintains wakefulness. As sunlight fades in the evening, the sedating hormone melatonin is produced, countering the effects of cortisol, and encouraging sleepiness. Blue light from excessive use of screens in the evening can reduce or delay the natural production of melatonin, decreasing slow-wave and rapid-eye movement (REM) sleep, two stages of the sleep cycle that are vital for cognitive functioning.[34][35]
LZ have demonstrated an ability to improve sleep patterns via their positive effects on the retina, and subsequent mitigation of blue light’s impact on melatonin.[36][37][38] In one study, 48 healthy adults with at least 6 hours of daily screen exposure participated in a 6-month placebo-controlled trial. LZ supplementation achieved significant improvement in overall sleep quality, as well as a reduction in headache frequency, eye strain, eye fatigue, and overall visual performance, compared to placebo. [39]
Lutein And Zeaxanthin Sharpen The Mind
LZ are stored in key locations in the brain,[40] and have exhibited important actions in support of cognitive health. Older adults who consumed higher amounts of dietary LZ displayed significantly greater word recall than those whose intake was considered low amongst almost 6,400 individuals. A strong predictor of better recall was higher dietary consumption of LZ-rich foods such as green leafy and dark yellow vegetables, eggs and fruit.[41] Furthermore, multiple placebo-controlled trials show that LZ supplementation improves cognitive function, episodic memory and visual learning in older adults.[42][43] Cognitive function has also been assessed in younger adults. Researchers deliberately chose a younger population (college students aged 18-30), to isolate treatment effects that could not be confounded by education status, underlying nutritional deficiency or cognitive impairment. Significantly, they found several distinct cognitive benefits, including verbal memory, executive function, complex attention and cognitive flexibility, which were all directly tied to increasing body levels of LZ.[44]
Yellow Carotenoids = Blue Skies
The positives of LZ for eye health are clear to see (pardon the pun), however there is more than meets the eye to these yellow carotenoids. Their promotion of healthy sleep in the face of ever-increasing screen use can benefit all, while their ability to support cognitive function, even in younger populations, further demonstrates their unique attributes.
So, there you are: LZ can help you achieve a sharper mind, more restful sleep, and a brighter outlook whatever your age. Are Lutein and Zeaxanthin your new favourite antioxidants? I believe eyes have it!
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