Quite extensive researches have been conducted for the biological roles of carotenoids including lutein in human health. Of carotenoids, which consists of at least 600 distinct plant pigments, lutein has been studied with deep interests as a special nutrition and protector for eye protection since the discovery of lutein (and zeaxanthin) as the only anti-oxidant carotenoid that accumulates in macula, the central part of the eye.

Because lutein is a carotenoid anti-oxidant that are present in blood stream and elsewhere over the entire body, it is also interesting to find other health impacts of this particular nutrition.

A review article published in Nutrition in October 2001, under the title The evolving role of carotenoids in human biochemistry. by G.J. Handelman at Department of Health and Clinical Science, University of Massachusetts, Lowell, MA, summarizes the role of lutein and zeaxanthin, in particular, and carotenoids in genenral. The role of beta-carotene and several other pro-vitamin A carotenoids in animal as vitamin A precursors was recoginized as the earliest findings of the biological functions of carotenoids. Following is the excerpt from the abstract of this article.
Because carotenoids (such as lutein and 9-cis beta-carotene) are excellent scavengers of singlet oxygen and other reactive oxygen species, substantial work was dedicated to their anti-oxidant aspects. Interestingly, the ability of radicals in cigarette smoke to degrade carotenoids might be responsible for the finding that high-dose dietary beta-carotene increased the incidence of of lung cancer in smokers. A new role for the polar carotenoids lutein and zeaxanthin was identified, when those carotenoids were found to constitute the macular pigment (the yellow spot at the center of the human retina). Many different carotenoids can be metabolized to products with retinoid activity, which might affect gene exptression and cell differentiation. The formation of retinoids from diverse carotenoids might account for a portion of their activities as anticancer agents. Studies of lycopene are underway. Carotenoids have emerged as the best single tissue marker for a diet rich in fruits and vegetables, and measurements of plasma and tissue carotenoids have an important role in defininf the optimal diets for humans.