Thus, while 20 mg/day of β-carotene in the form of a supplement is sufficient to raise blood concentrations to a range reported to be associated with an increase in lung cancer risk, the same amount of β-carotene in foods is not. Micozzi et al. (1992) demonstrated that 30 mg/day of supplemental β-carotene produced more than a five-fold increase in plasma β-carotene compared to 29 mg/day of β-carotene from carrots.
Based on these considerations, the existing recommendation for consumption of five or more servings of fruits and vegetables per day is supported because this would provide 3 to 6 mg/day of β-carotene. A UL has not been set for β-carotene or carotenoids. Instead, it is concluded that β-carotene supplements are not advisable for the general population. This conclusion is based on a totality of evidence that includes several large-scale randomized trials of supplemental β-carotene. These trials indicate a lack of evidence of overall benefit on total cancer or cardiovascular disease and possible harm in certain subgroups such as current smokers or asbestosexposed subjects. This advisement does not pertain to the possible use of supplemental β-carotene as a provitamin A source or for the prevention of vitamin A deficiency in populations with inadequate vitamin A nutriture or in patients suffering from erythropoietic protoporphyria.
As described earlier, β-carotene and other carotenoids have been shown to modulate a variety of intermediate endpoints. However, studies validating that changes in an intermediate endpoint are predictive of changes in a health outcome are critically needed. As an example, macular pigment optical density (MPOD) is a promising intermediate marker for age-related macular degeneration (AMD), but human studies validating this endpoint prospectively are needed, as are studies demonstrating that changes in MPOD are predictive of changes in risk of macular degeneration.
As a corollary, studies are needed on the effects of long-term depletion of β-carotene and subsequent repletion, with an evaluation of validated intermediate endpoints.
Significantly more research is needed on health effects of dietary carotenoids other than β-carotene. Possible associations between lycopene and decreased prostate cancer risk, between lutein and zeaxanthin and lowered risk of AMD, and between α-carotene or lutein and various cancers have to be evaluated in additional