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DRI DIETARY REFERENCE INTAKES FOR Vitamin C, Vitamin E, Selenium, and Carotenoids
lowest quintile (cutpoint not stated). The mean concentration of serum β-carotene in persons who subsequently developed lung cancer was 0.47 µmol/L (25 µg/dL), compared to 0.54 µmol/L (29 µg/dL) in persons who remained free of disease.
Nomura et al. (1985) conducted a prospective study of 6,860 men of Japanese ancestry in Hawaii; 74 men subsequently developed lung cancer. Men who later developed lung cancer had lower serum β-carotene concentrations (0.37 µmol/L [20 µg/dL]) than control subjects (0.54 µmol/L [29 µg/dL]). Similar results were reported in the Basel Prospective Study. Men who later developed lung cancer (n = 68) had α- plus β-carotene serum concentrations of 0.30 µmol/L (16 µg/dL) versus 0.43 µmol/L (23 µg/dL) in survivors (Stahelin et al., 1991). The Multiple Risk Factor Intervention Trial (MRFIT) cohort study had prediagnostic serologic data on 66 lung cancer cases and 131 control subjects (Connett et al., 1989). Lung cancer cases had lower serum β-carotene concentrations (mean of 0.17 µmol/L [9 µg/dL]) and total carotenoid concentrations (1.62 µmol/L [87 µg/dL]) compared to the control subjects (0.22 µmol/L [12 µg/dL] and 1.84 µmol/L [99 µg/dL]), respectively. The absolute carotenoid concentrations in this study are lower than those in the previous studies, which may be a consequence of long-term storage of the samples at −50°C, rather than at −70°C or colder as is recommended for carotenoids.
As for dietary studies, the majority of the studies of carotenoids and lung cancer risk have relied upon the U.S. Department of Agriculture (USDA) Nutrient Database for Standard Reference, Release 13, which does not contain estimates of the amount of carotenoids in various food items, but simply contains estimates of provitamin A activity. With the release of a new carotenoid database in 1993 (Mangels et al., 1993), quantitative studies relating consumption of individual carotenoids to lung cancer risk are now available. Le Marchand et al. (1993) found that higher dietary intake of α-carotene, β-carotene, and lutein was significantly associated with lower lung cancer risk in both men and women. Optimal levels of intake for each of these three carotenoids were as follows: β-carotene more than 4.0 mg/day for men and more than 4.4 mg/day for women; α-carotene more than 0.6 mg/day for men and more than 0.7 mg/day for women; and lutein more than 3.3 mg/day for both males and females. Ziegler et al. (1996a) also found significant inverse trends for dietary α- and β-carotene and a marginally significant effect for lutein and zeaxanthin with risk of lung cancer. Optimal levels in this study were as follows: β-carotene 2.5–5.9 mg/day; α-carotene more than 1.5 mg/day; and lutein and zeaxanthin more than 4.2 mg/day.