Carotenoids including beta-carotene, lutein, zeaxanthin, and lycopene are highly insoluble to water, raising a concerns of interestinal absoption of these important nutritions after oral ingestion. Several studies have been conducted to test whether the consumption of food or dietary supplements rich in carotenoids incease the serum level of these nutritions. In one study [B. Olmedilla, et al. April 2002. A European multicentre, placebo-controlled supplementation study with alpha-tocopherol, carotene-rich palm oil, lutein or lycopene: analysis of serum responses. Clin. Sci. (London) 102(4):447-56], serum response of carotenoids and tocopherols was tested upon supplementation with carotenoids from natural extracts (alpha- carotene + beta-carotene, lutein or lycopene; 15 mg per day) and/or with alpha-tocopherol (100mg per day) in a multicentre, placebo-controlled intervention study in 400 healthy male and female volunteers, aged 25-45 years, from five European regions (France, Northern Ireland, Republic of Ireland, The Netherlands, and Spain). Supplementation with alpha-tocopherol increased serum alpha-tocopherol levels, while producing a marked decrease in serum gamma-tocopherol. Supplementation with alpha- + beta-carotene (carotene-rich palm oil) resultsed in 14-fold and 5-fold increases respectively in serum levels of these carotenoids. Supplementation with lutein (from marigold extracts) elevated serum lutein (approximately 5-fold), zeaxanthin (approximately doubled), and ketocarotenoids (although these were not present in supplement), whereas lycopene supplementation (from tomato paste) resulted in a 2-fold increase in serum lycopene. The isomer distributions of beta-carotene and lycopene in serum remained constant regardless of the isomer composition in the capsules. In Spanish volunteers, additional data showed that the serum response to carotenoid supplementation reached a plateau after 4 weeks, and no significant side effects (except carotenodermia) or changes in biochemical or haematological indices were observed throughout the study.

Another study [C.L.Rock et al. March 2002. Diet and lifestyle correlates of lutein in the blood and diet. J. Nutr. 132(3): 525S-530S] investigates the correlations between dietary lutein + zeaxanthin intake and the determinants of serum lutein and zeaxanthin concentrations in a heterogeneous community-based sample of adults aged 18-92 Y, recruited and examined at three U.S. sites (n=2,786). The study also aimed to identify the determinants of change in serum lutein concentration from baseline to 1 year in a subset of 1,396 study participants followed prospectively. Demographic characteristics (age, sex, race/ethnicity, education), body mass index and lifestyle factors (exercise, sun exposure, smoking, alcohol consumption) were significantly (P < 0.05) associated with dietary lutein + zeaxanthin intake. Demographic characteristics, dietary intake, serum cholesterol concentration, body mass index, and smoking explained 24% of the vairance in serum lutein concentration. Race/ethnicity, education level, and smoking had the strongest associations with serum lutein concentration. Every 10% increase in dietary lutein + zeaxanthin intake was associated with a 2.4% increase in serum lutein concentration.

These studies clearly demonstrate that dietary intake of lutein and other carotenoids are positively correlated to the enhanced lutein and other carotenoid levels in all cases, although there are some variances depending on other factors. It has been observed that there is an inverse relationship between dietary or serum lutein levels and risk for age-related macular degeneration and cataracts. Similarly, the serum level of carotenoids have been positively correlated to the prevention of cancer and various diseases. In conclusion, the evidences are strongly in favor of taking lutein in food or dietary supplement for better health.