high-dose supplementation of β-carotene daily for several years. This finding is not inconsistent with the results of the metabolic studies, because the trials were done in free-living individuals taking a supplement of β-carotene each day, which most likely is not consumed concurrently with an entire day's intake of other carotenoids from food.

As discussed elsewhere in this document, this report does not establish a requirement for β-carotene or other carotenoids for any gender or life stage group. This issue will be considered in a subsequent report when addressing vitamin A. However, the following summarizes findings regarding carotenoid status, as measured by serum carotenoid concentrations, in different groups of the population.

If plasma carotenoid concentrations are considered as an indicator of adequacy with regard to reducing risk of chronic disease, it becomes apparent that certain subgroups of the population are known to have notably lower circulating concentrations of carotenoids. Thus, consumption of carotenoid-containing foods may have to be greater in these groups in order to achieve plasma carotenoid concentrations that are associated with a reduced risk of chronic disease (Table 8-3).

Serum carotenoid concentrations were measured in the Third National Health and Nutrition Examination Survey (NHANES III). As shown in Appendix Table F-4, serum β-carotene concentrations were lower during the period of adolescence and early adulthood in this U.S. population survey. The average concentration in children was approximately 0.34 µmol/L (18 µg/dL), which dropped to 0.28 µmol/L (15 µg/dL) or less in teenagers and did not return to childhood concentrations until the fourth decade (the thirties) for women, and the fifth decade (the forties) for men. This lower level during adolescence is also evident for α-carotene (Appendix Table F-5), β-cryptoxanthin (Appendix Table F-6), and lutein/zeaxanthin (Appendix Table F-7), but not lycopene (Appendix Table F-8). This may reflect relatively greater consumption of tomato products compared to other vegetables by adolescents in the United States.