Lutein and Its Eye Effects

Introduction

There is an increasing curiosity among researchers, scientists, and clinicians to search for superfoods that can prevent and treat chronic diseases. Carotenoids are nutrient-rich food having exemplary antioxidant properties. They are present in fruits and vegetables and help in reducing the oxidative properties of certain chronic diseases of the body and the eyes.

What Are Lutein?

Lutein are fat-soluble oxygen-enriched colored pigments (xanthophyll) present in fruits and vegetables. They are responsible for imparting red, yellow, and orange hues to different fruits and vegetables. Humans derive most of their lutein from their diet.

What Is the Chemical Structure of Lutein?

Lutein, like all carotenoids, are primarily carbon-containing compounds. The only difference between luteins and their other carotenoid counterparts is the presence of oxygen atoms in their chemical structure. The presence of oxygen has a major functional implication.

How Are Lutein Distributed in the Human Body?

Lutein are mainly found in the inner plexiform layer (consists of synapses between the second and third motor neurons) and Henle’s fiber layer (outer layer) of the retinal nerve fiber in humans. Along with other carotenoid compounds like zeaxanthin, it is present in the macula (part of the retina) of the eyes. The amount of lutein decreases as one moves away from the macula. Overall, luteins are present in different parts of the eyes, including the iris, uvea, and ciliary body of the eyes.

How Are Lutein Absorbed and Digested in the Body?

Lutein are not synthesized in the human body. It is ingested by humans through their food. The ingested lutein is then absorbed by the mucosa of the bowel, and from there, it reaches the liver through the lymphatic system. In the liver, the lutein get attached to the lipoproteins and are distributed to the other peripheral tissues of the body, especially the retina.

What Are the Contributing and Non-contributing Factors Related to Lutein Absorption?

There are several factors that prevent the absorption of lutein. These include:

• Fiber-rich diet.

• Food rich in other carotenoids.

• Iron and zinc deficiency.

• Protein deficiency.

• Orlistat drugs.

• Alcoholism.

• Smoking.

On the other hand, the presence of mono and diglyceride fats helps in enhancing the absorption of lutein.

How Does the Lutein Work?

Lutein by and large have extremely potent antioxidant capacity. In the eyes, they reduce the continuous exposure to blue light, thus reducing the phototoxic damage caused to the photoreceptor cells of the retina. Lutein mainly act by reducing the release of reactive oxygen species (ROS).

What Is the Major Function of Lutein in the Human Body?

Leutin play an important role in reducing oxidative stress related to several chronic systemic diseases and age-related disorders.

• They are oxygen scavengers. They remove free radicals present in the body, thus preventing damage caused by free radicals to the body tissues.

• They exhibit anti-inflammatory properties.

• Apart from the above-mentioned functions, carotenoids like lutein also have anti-cancer properties.

• Lutein regulate the immune systems and the inflammatory pathway.

What Are the Dietary Sources of Lutein?

Lutein are the naturally occurring pigmented compounds most frequently found in fruits and vegetables such as tomatoes, sweet potatoes, turnips, peas, bell pepper, lettuce, spinach, kale, and egg yolk.

Where Are the Lutein Stored Inside the Human Body?

Lutein are stored in different body tissues, including the brain. The retinal and other ocular structures show a high build-up of lutein. The macula of the eye contains yellow-colored xanthophyll pigment known as macula lutea.

What Is the Ideal Dietary Intake of Lutein for Humans?

The recommended dietary intake of lutein varies based on the diet consumed by a population. The western diet lacks vegetables, hence consumption of 1.7mg per day of lutein is preferred.

Pacific country's diet is highly enriched with fruits and vegetables, hence the intake of lutein in their diet reaches up to 25 mg per day. Therefore, based on the diet consumed by people of different regions, the daily intake of lutein should be between 0.67 to 20 mg per day.

What Is the Role of Lutein in Various Ocular Diseases?

Lutein play an important role in regulating chronic eye disorders. For example, age-related macular diseases, cataracts, and diabetic retinopathy are influenced by lutein. The mechanism involved in the initiation and progression of various disorders is oxidative stress which damages the cells of the retina.

Age-Related Macular Diseases:

• The presence of macular pigment reduces the risk of oxidative stress. Several factors like age, repeated blue light exposures, etc., lead to the destruction of the retinal cells and reduce the macular pigment by releasing reactive oxygen species like hydrogen peroxide, free radicals, and superoxides that are responsible for oxidative stress.

• Lutein prevent the destruction of the cells by removing the reactive oxygen species.

Cataracts:

• A cataract is the most common age-related cause of blindness. It is defined by the deposition of insoluble crystalline protein post-modification in the lens. The modification is brought about by various processes, including the oxidation process. This results in lens opacification.

• Carotenoids like lutein and zeaxanthin help protect the lens protein from oxidative damage by scavenging the free radicals, hence preventing senile cataracts.

Diabetic Retinopathy:

• Diabetic retinopathy is the most common vascular disease of the retina prevalent in type I and II diabetes patients. Increased glucose concentration in the blood results in biochemical changes in the retinal blood vessels, ultimately leading to their damage by oxidative stress.

• Lutein, macular pigments, and carotenoids prevent damage to the retinal blood vessels by enhancing the insulin sensitivity of the cells. They also have an anti-inflammatory effect on the retinal vessels.

Is Consuming a Diet Rich in Lutein Safe?

In a well-balanced diet, there is an adequate intake of lutein. In case of inadequate diet or in the presence of chronic diseases, there is a need to supplement the normal diet with lutein. Lutein consumption is totally safe. They do not have any teratogenic (cause developmental deformity) or carcinogenic (cancer-causing) potential. The joint expert committee of food additives has established 2 mg/Kg per day as the upper limit for luteins intake.

Though lutein do not cause any severe toxicity, a few side effects have been reported with chronic lutein intake; these include:

• Increased risk of lung cancer, especially among smokers.

• Deposition of crystalline protein inside the retina (crystalline maculopathy).

Conclusion

Lutein belong to an important class of molecules that are known for their antioxidant and anti-inflammatory properties. A well-balanced diet consisting of fresh fruits and vegetables is a rich source of luteins. Lutein prevent the oxidative damage caused to the ocular tissues and enhance the overall vision.