Lutein: An Essential Carotenoid for Human Health
Lutein is one of over 600 known carotenoids found in nature and has been proven to have positive effects on human health, such as benefiting the nervous system, eye diseases, reducing cancer risks, and improving cardiovascular health. Since the human body cannot produce lutein naturally, it can only be obtained through diet
[1].
Sources of Lutein
Common dietary sources of lutein are yellow or orange-colored foods such as carrots, corn, spinach, kale, oranges, pumpkins, and some fish and eggs also contain lutein
[2]. The metabolism, absorption, and assimilation of lutein in the diet is a complex process. Lutein’s bioavailability is influenced by food conditions, and it requires processing and heating to be released from food for better absorption
[3]. Studies show that the source of lutein from different foods significantly affects the concentration of lutein in the body
[4].
Relationship between Lutein and Eye Health
Research suggests that the human retina contains various carotenoids, primarily lutein and zeaxanthin. Analyzing lutein and zeaxanthin levels in the eye shows concentrations in the macula and retina 1000 times higher than in other tissues, indicating their crucial impact on visual health
[5].
Lutein in the retina acts as an antioxidant and a filter for harmful blue light, protecting the macula from blue light damage and eliminating reactive oxygen species. It is believed to protect the eyes, helping to reduce the risk of age-related macular degeneration and cataracts and improving recovery time after exposure to light
[6].
Forms of Lutein
Lutein can exist as free lutein or lutein esters. Free lutein is more abundant in fruits and vegetables found in nature
[4]. Lutein esters’ structure requires hydrolysis by the fat enzyme secreted by small intestine cells to release free lutein. Then, it combines with the receptors of the small intestine cells before absorption into the blood. Free lutein in the blood mainly binds with high-density lipoprotein cholesterol for transportation
[7].
Free lutein is transported to the retinal pigment epithelial cells through the blood and combines with retinol-binding protein before entering photoreceptor cells in the retina, where it exerts its physiological effects
[8]. Lutein esters are generally found in the form of lutein diesters in nature, meaning lutein carries two ester groups, which need to be cleaved for absorption in the body. Free lutein, on the other hand, does not require this process and can be directly absorbed in the intestine
[9]. Recent research indicates that different forms of lutein result in varying serum lutein concentrations, showing differences in their absorption rates
[4].
How to Choose Lutein Forms with Different Absorption Rates
Lutein supplements available in the market are predominantly provided in free lutein and esterified forms, aiming to promote eye health
[5]. Studies indicate that both free lutein and lutein esters can significantly increase lutein levels in the blood, and the measurement of macular pigment optical density (MPOD) demonstrates a significant increase in lutein content. However, research shows that the free lutein group (38%) had a significantly greater increase in concentration than the lutein ester group (17%)
[7].
Clinical studies have suggested that healthy subjects (blood lutein levels <20 µg/dL) supplementing different forms of lutein—free lutein (12.2 mg) and lutein esters (27 mg, equivalent to 13.5 mg of free lutein)—for 28 days found a 5.2-fold increase in serum lutein concentration in the free lutein group. Moreover, the free lutein group showed a significantly 17% higher increase in concentration compared to the ester group. Further analysis revealed a 23% significantly higher absorption rate of free lutein compared to esterified lutein
[4]. Other research suggests that free lutein has a higher bioavailability than lutein esters because lutein esters must be metabolized into free lutein in the intestines before absorption
[10]
[11].
Read more: [2023 Latest] 12 Recommended Lutein Brands: Experts’ Selection of 4 Key Points for Lutein!
Further reading: Taking Lutein Doesn’t Help Your Eyes? Experts Analyze 3 Reasons and 3 Key Points for Choosing Lutein!
How to Consume Lutein for Better Absorption
Lutein is a fat-soluble nutrient, and an increased intake of dietary fats can enhance its absorption. Food processing and heating also assist in the release of lutein, promoting better absorption
[3]. Animal studies have shown that concurrent administration of oil and lutein can significantly increase lutein concentrations in the body, demonstrating the role of fats in aiding lutein absorption
[12].
Clinical research found that adding lipid-rich avocados to salad dressings of healthy subjects significantly increased post-meal serum levels of α-carotene, β-carotene, and lutein, indicating that lipids do indeed aid in lutein absorption
[13]. In another clinical study, simultaneous supplementation of lutein and fish oil (DHA) supplements increased macular pigment optical density, which helps prevent age-related macular degeneration
[14]. Therefore, it is recommended to consume lutein after meals for improved absorption.
Lutein Safety
In general, lutein supplementation is considered safe. The U.S. FDA categorizes lutein as “Generally Recognized As Safe” (GRAS), which means it has no adverse effects even with long-term consumption. The Joint FAO/WHO Expert Committee on Food Additives (JECFA) recommends a daily acceptable intake (ADI) of 2 mg/kg body weight for lutein and synthetic zeaxanthin. The European Food Safety Authority (EFSA) recommends a daily intake of 1 mg/kg body weight
[15]. The Ministry of Health and Welfare in Taiwan recommends that the daily lutein supplementation should not exceed 30 mg
[16]. Some studies have used high doses of lutein without adverse reactions, indicating that lutein supplementation in the diet is not toxic
[11]. If you have concerns about lutein supplementation, it is advisable to consult with your physician or nutritionist before making a decision.
Conclusion
Clinical research suggests that the free form of lutein, with better absorption, is recommended for lutein supplementation. Taking lutein after meals enhances its absorption. Furthermore, lutein requires time to accumulate for effective eye care, so consistent and steady supplementation, combined with other nutrients, can further improve eye comfort and overall visual health!
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