Lipid-lowering drugs have been shown to decrease serum carotenoids dramatically (Elinder et al., 1995). In a double-blind, randomized trial, treatment with cholestyramine (a lipid-lowering resin) for 4 months and probucol (antioxidant and lipid-lowering drug) for 2 months resulted in a 65 percent reduction in serum β-carotene and a 51 percent reduction in lycopene. The reductions were attributed to reduced intestinal absorption of lipids by cholestyramine and reduced lipoprotein particle number and size by probucol. Sucrose polyester (olestra), the nonabsorbable fat substitute, lowered carotenoid absorption when consumed at the same time as carotenoids (Koonsvitsky et al., 1997; Weststrate and van het Hof, 1995). Plant sterol-enriched margarines (Weststrate and Meijer, 1998) and dietary pectin supplementation also decreased β-carotene absorption (Rock and Swendseid, 1992).

Competitive interactions among different carotenoids during the absorptive process have been studied. Recipients of daily β-carotene supplements in either 12-mg or 30-mg capsules for 6 weeks had significantly lower plasma lutein concentrations than subjects who consumed both β-carotene and lutein from food sources (Micozzi et al., 1992). In addition, plasma β-carotene was higher in the subjects receiving β-carotene as supplements rather than as food, demonstrating the greater bioavailability of this source. Interactions between β-carotene and lutein have also been described by other investigators. When subjects were given purified crystalline β-carotene and crystalline lutein in a combined dose, β-carotene significantly reduced the serum area under the curve (AUC) value (a measure of total absorption) for lutein (Kostic et al., 1995). Lutein in a combined dose with β-carotene significantly enhanced β-carotene AUC in those subjects whose AUC for β-carotene (when dosed alone) was the lowest.

These studies (White et al., 1994) indicate that two carotenoids administered concurrently in controlled settings can affect the absorption of each other. Several investigators have examined the effect of daily supplementation with high-dose β-carotene on plasma concentrations of other carotenoids in participants in multiyear cancer prevention intervention trials (Albanes et al., 1997; Mayne et al., 1998; Nierenberg et al., 1997; Wahlqvist et al., 1994). These studies suggest no overall adverse effect on other carotenoids with