An examination of human studies using dietary interventions with carotenoid-containing foods is necessary to determine the plasma carotene concentrations that an optimal diet would be expected to produce. In a controlled diet study (Micozzi et al., 1992), plasma β-carotene concentrations in the men who received the low carotenoid diet (less than 2 mg/day) to which broccoli had been added to provide 6 mg/day of carotenoids (3 mg of β-carotene, 3 mg of lutein) were raised significantly from 0.30 µmol/L (16 µg/dL) at baseline to 0.49 µmol/L (26 µg/dL) after six weeks, as were plasma lutein concentrations (from 0.38 µmol/L [22 µg/dL] to 0.63 µmol/L [36 µg/dL]). Plasma lycopene declined with this intervention because the baseline diet as well as broccoli was low in the content of lycopene and other carotenoids.
The Minnesota Cancer Prevention Research Unit feeding studies evaluated three experimental diets (two of which included carotenoids) and one control diet given for 9 days each to 23 young nonsmoking men and women. Persons on the control diet had a plasma β-carotene concentration of 0.26 µmol/L (14 µg/dL); 5 mg/day β-carotene from food increased plasma β-carotene to 0.37 µmol/L (19.5 µg/dL). When β-carotene from food was increased to 42 mg/day, plasma β-carotene increased further to 0.83 µmol/L (44 µg/dL) (Martini et al., 1995). Yong et al. (1994) studied dietary carotenoid intake and plasma carotenoids cross-sectionally in premenopausal nonsmoking women; the population had a geometric mean β-carotene intake of approximately 3 mg/day and a geometric mean plasma β-carotene concentration of 0.30 µmol/L (15.8 µg/dL). For total carotenoids, the geometric mean level of intake was 6.6 to 8.1 mg/day, with a total carotenoid concentration in plasma of approximately 1.51 µmol/L (80 µg/dL). A randomized, controlled trial on the effect of increasing fruit and vegetable intake for 8 weeks on plasma micronutrient concentrations was conducted with 87 subjects in New Zealand (Zino et al., 1997). β-Carotene intake increased from about 2.0 mg/day at baseline to 4.7 mg/day at week 4. This resulted in a mean plasma β-carotene increase from 0.34 µmol/L (18 µg/dL) at baseline to 0.48 µmol/L (25 µg/dL) at 4 weeks.
These data, although in varying populations, suggest that 3 to 6 mg/day of β-carotene from food sources is prudent to maintain plasma β-carotene concentrations in the range associated with a lower risk of various chronic disease outcomes (see Table 8-3).