The Journal of Nutrition Vol. 127 No. 8 August 1997, pp. 1475-1479
Copyright ©1997 by the American Society for Nutritional Sciences

Accumulation and Clearance of Capsanthin in Blood Plasma after the Ingestion of Paprika Juice in Men^1,2

Syunji Oshima, Hideki Sakamoto, Yukio Ishiguro, and Junji Terao^{*, 3}

Kagome Research Institute, Kagome Co. Ltd., Nishinasuno, Tochigi 329-27 Japan and ^* National Food Research Institute, Ministry of Agriculture, Forestry and Fisheries, Tsukuba, Ibaraki 305 Japan

ABSTRACT

INTRODUCTION

SUBJECTS AND METHODS

RESULTS

DISCUSSION

FOOTNOTES

LITERATURE CITED

ABSTRACT

The pharmacokinetics of dietary capsanthin was measured in four male volunteers to assess the bioavailability of oxygenated carotenoids (xanthophylls). Capsanthin was used because this carotenoid was not detected in the men's plasma before ingestion of paprika juice. Supplementing capsanthin-rich paprika juice for 1 wk (equivalent to three doses of 5.4 µmol capsanthin/d; 16.2 µmol/d), the level of capsanthin reached a plateau (0.10-0.12 µmol/L) between d 2 and 7 and was not detectable by d 16. Capsanthin was distributed in the plasma lipoproteins (VLDL, 13 ± 3%; LDL , 44 ± 3%; HDL, 43 ± 3%) at the end of the experiment. In a separate experiment involving the single ingestion of paprika juice (equivalent to 34.2 µmol capsanthin) in the same men, the plasma concentration of capsanthin ranged from 0.10 to 0.29 µmol/L at 8 h after ingestion. In contrast, the elevation of the plasma concentration of an acyclic hydrocarbon carotenoid, lycopene, by a single ingestion of tomato soup (equivalent to 186.3 µmol lycopene) in the same subjects was minimal (0.02-0.06 µmol/L). The areas under the curves (AUC) for capsanthin between 0 and 74 h and for lycopene between 0 and 72 h were 4.68 ± 1.22 and 0.81 ± 0.17(µmol·h)/L, respectively. The half-lives (t_1/2) were calculated to be 20.1 ± 1.3 and 222 ± 15 h for capsanthin and lycopene, respectively. We conclude that the clearance of capsanthin is much faster than that of lycopene, although capsanthin is transported into plasma lipoproteins in larger amounts. This polar carotenoid may be metabolized in the human body more rapidly than lycopene. These data justify further research on the physiological functions of capsanthin and other xanthophylls.

INTRODUCTION

There is much interest in the role of dietary carotenoids in the prevention of degenerative diseases such as cancer and cardiovascular disease (Gaziano and Hennekens 1993, Peto et al. 1981, van Poppel 1993). Epidemiological studies suggest that the incidence of human cancer is inversely correlated with the dietary intake of carotenoids and their concentration in blood plasma (Ziegler 1988). However, there have been contradictory reports concerning the use of -carotene for cancer prevention (Blot et al. 1993, Heinonen and Albanes 1994, Omenn et al. 1996). It has been demonstrated recently that supplementation of -carotene in healthy men produced neither benefit nor harm in terms of the incidence of cancer and cardiovascular disease (Hennekens et al. 1996).

A variety of carotenoids are present in commonly eaten foods and these compounds accumulate in tissues and blood plasma. About 20 carotenoids, including their metabolites, have been identified in human plasma (Khachick et al. 1995). Animal studies and cultured cell studies have shown that some carotenoids other than -carotene possess antitumor properties that are equivalent or superior in effectiveness to -carotene (Levy et al. 1995, Murakoshi et al. 1992, Pung et al. 1988, Tanaka et al. 1994). Thus the bioavailability of carotenoids other than -carotene in humans should be clarified to assess the anticarcinogenic effect of dietary carotenoids. Mathews-Roth et al. (1990) studied the absorption and distribution of [¹⁴C]-canthaxanthin, a typical oxygenated carotenoid (xanthophyll), and [¹⁴C]-lycopene, an acyclic hydrocarbon carotenoid, in rats and rhesus monkeys. They showed that the liver accumulated the largest amount of both radioactive compounds, and that the clearance of lycopene was much slower than that of canthaxanthin. Interestingly, the distribution patterns of each carotenoid in the organs differed; for example, lycopene was the predominant carotenoid in the adrenal and testis (Kaplan et al. 1990). In a study of the distribution of carotenoids in human plasma lipoproteins, Manago et al. (1992) demonstrated that LDL accumulated more -carotene than did HDL. Nevertheless, the distribution and clearance of carotenoids in human blood plasma are still obscure. To our knowledge, no studies have been performed on the pharmacokinetics of xanthophylls in human plasma.

In the present study, capsanthin, a typical pigment in paprika, was selected as a representative xanthophyll. Capsanthin accumulation and distribution in human plasma were investigated by single and periodic ingestion of paprika juice in male volunteers. The bioavailability of this xanthophyll and that of lycopene is discussed on the basis of the pharmacokinetic data obtained after a single ingestion of capsanthin and lycopene.

---

SUBJECTS AND METHODS

Subjects. Four healthy male volunteers aged 26-30 y participated in this study. They were nonsmokers and did not consume alcohol. The same subjects participated in all of the studies. The procedures applied were in accordance with the Helsinki Declaration, updated in Tokyo, Japan in 1975. The study protocol was approved by the Ethics Committee of Showa Women's University, Tokyo, Japan. No abnormal values were found for plasma cholesterol, glutamic-oxaloacetic transaminase and glutamic-pyruvic transaminase levels before or after the trial.

Study design. The experiment consisted of the following three parts: Study 1, a periodic ingestion of capsanthin-rich paprika juice; Study 2, a single ingestion of the same paprika juice; and Study 3, a single ingestion of lycopene-rich tomato soup. There were intervals of ~3 mo between each study. During the experiment, the subjects avoided consuming vegetable juice, synthetic carotene drinks and supplements containing carotenoids and vitamins. Before starting Study 3, diets of low lycopene content were served to the subjects for 3 mo to maintain low lycopene concentrations in blood plasma before the study.

Diets. Paprika was purchased at local distributors. The juice, which was the source of dietary capsanthin, was made from the paprika using an electric juicer. Tomato paste was obtained from TAT (Istanbul, Turkey), and tomato soup was prepared by mixing the paste with cream soup (fat concentration: 2.8 g/100 g). Capsanthin and other carotenoids were extracted from paprika juice using hexane and ethyl acetate (9:1, v/v) after saponification with KOH (10.7 mol/L) for 30 min. Lycopene and -carotene were extracted from tomato juice with benzene and methanol, respectively. The concentration of each carotenoid in paprika juice and tomato soup was determined by the same method as those for plasma carotenoids described later.

In Study 1, 0.16 kg of paprika juice (equivalent to a single dose of 5.4 µmol capsanthin, 2.3 µmol zeaxanthin, 2.2 µmol cryptoxanthin and 6.1 µmol -carotene) was regularly ingested by the subjects with their daily diets three times a day for 1 wk. Its taste was acceptable. In Study 2, the paprika juice (1.013 kg, the equivalent of 34.2 µmol of capsanthin) was ingested once by the same subjects with breakfast In Study 3, tomato soup (300 g, containing 186.3 µmol of lycopene and 5.7µmol of -carotene) was also ingested with breakfast.

Sample preparation. Blood samples were obtained at specific intervals during each study period. Each blood sample was collected from the subjects into a test tube containing disodium EDTA, and plasma fractions were prepared by immediate centrifugation at 1087 × g for 20 min. Blood samples for measuring the distribution of carotenoids and -tocopherol in plasma lipoproteins were collected from each of the four subjects at the end of Study 1. The lipoproteins were then fractionated by density-gradient ultracentrifugation and separated into VLDL (d < 1.006 kg/L, containing chylomicrons), LDL (1.006 < d < 1.063 kg/L), and HDL (1.063 < d < 1.21 kg/L) according to the method of Goldstein et al. (1983). Both plasma and lipoproteins were stored at 80°C until use within 1 wk.

Analyses. Plasma carotenoids and -tocopherol concentrations were determined by HPLC of plasma and plasma lipoprotein extracts. The sample (200 µL) was withdrawn and 1.0 mL of ethanol solution of trans--8-apocarotenal was added to the plasma as an internal standard. A solution of n-hexane and dichloromethane (4:1, v/v, 5.0 mL) was added to the mixture and centrifuged (1087 × g, 10 min). The supernatant (4.0 mL) was evaporated under nitrogen gas. The residue was dissolved in 200 µL of solvent mixture (methanol/acetonitrile/dichloromethane, 7:7:2, v/v/v) for HPLC analysis.

Carotenoids were quantified by HPLC using a Lichrospher RP18-5 column (E. Merck, Darmstadt, Germany) with mobile phases of methanol, acetonitrile, dichloromethane and water (for hydrocarbon carotenoids 7:7:2:0.16, v/v/v/v, and for xanthophylls 7:7:2:3.2, v/v/v/v) at a flow rate of 1.0 mL/min. The effluent was monitored at 450 nm using a Shimadzu SPD-10AV spectrophotometric detector (Shimadzu, Kyoto, Japan). A Shim-Pack CLC-ODS column (Shimadzu) with a mobile phase of methanol and acetonitrile (1:9, v/v) was used for the determination of -tocopherol. The flow rate was set at 2.0 mL/min, and the effluent was monitored with a spectrofluorophotometer, Shimadzu RF-10A (Shimazdu), with extinction at 290 nm and emission at 325 nm. Each compound was identified on the basis of its retention time. Carotenoid standards other than capsanthin were purchased from Sigma Chemical (St. Louis, MO). Capsanthin was obtained from Extrasynthese (Genay, France). -Tocopherol was a gift from Eisai (Tokyo, Japan). The concentration of cholesterol in plasma lipoproteins was determined enzymatically using the Cholesterol E test-Wako (Wako Pure Chemicals, Tokyo, Japan).

Calculation of pharmacokinetic parameters. The area under the curve (AUC) was calculated for plasma carotenoid concentration-time curves using a linear trapezoidal equation (Phillips and Taylor 1973). The AUC_{0-16 d} was calculated by measuring plasma carotenoid concentrations between 0 and 16 d after starting Study 1. For Studies 2 and 3, the AUC_{0-74 h} of capsanthin and the AUC_{0-72 h} of lycopene were calculated by measuring capsanthin and lycopene concentrations between 0 and 74 h, and 0 and 72 h, respectively. The time courses of the plasma concentration for capsanthin and lycopene were analyzed on the basis of the two-compartment model (Rowland et al. 1973). The half-lives (t_1/2) of capsanthin and lycopene were calculated from the elimination phases of logarithmic-concentration curves.

Statistical analysis. Values in the text are means ± SEM. Data were tested for normality with the Kolmogorow Smirnov D Statistic (Zar 1974). All data were analyzed parametrically because these sets were normally destributed. Statistical analysis was evaluated by repeated-measures ANOVA, followed by Tukey's test (Steel and Torrie 1982) to identify significantly different means using VisualStat software (StatSoft, Tulsa, OK). Significance was set at P < 0.01.

---

RESULTS

Changes in plasma capsanthin and other carotenoid concentrations by the periodic ingestion of paprika juice. No capsanthin was detected in the plasma of subjects before Study 1 (Fig. 1). However, capsanthin was found in their plasma within 1 d of ingestion of paprika juice. A significant elevation of capsanthin concentration was observed between d 0 and 1, and its level was at a plateau between d 2 and 7 (0.10-0.12 µmol/L) (Fig. 2). Capsanthin was undetectable in plasma by d 16. The concentrations of plasma zeaxanthin/lutein and cryptoxanthin were both elevated during the period of periodic ingestion (d 0-7) and decreased after d 7. On the other hand, the plasma -carotene concentration did not change significantly on d 1 or 2 but was significantly greater on d 7 and 9. The AUC_{0-16 d} of each carotenoid during the period of paprika juice ingestion was obtained from the individual plasma carotenoid concentration-time curves in Figure 2. The values, expressed as (µmol·d)/L, were as follows: capsanthin, 1.21 ± 0.11; zeaxanthin/lutein, 2.83 ± 0.40; cryptoxanthin, 2.58 ± 0.25; and -carotene, 0.80 ± 0.39. Although the mean AUC_{0-16 d} value of capsanthin was lower than those of zeaxanthin/lutein and cryptoxanthin, no significant difference was observed among the three carotenoids (P > 0.01). -Carotene exhibited the lowest AUC_{0-16 d} value among the carotenoids tested and that value was significantly lower than those of zeaxanthin/lutein and cryptoxanthin (P < 0.01).

---

Fig. 1. A typical HPLC chromatogram for the detection of capsanthin in plasma extracts. (A ) Extract from a subject just before the start of Study 1; (B ) extract from the same subject at d 1 after starting ingestion. A Lichrospher RP18-5 column with a mobile phase of methanol, acetonitrile, dichloromethane and water (7:7:2:3.2, v/v/v/v) was used. Elution was at 1.0 mL/min and the absorbance at 450 nm was measured. Each peak was identified by the coincidence of the retention time with that of standard compounds as follows: 1, capsanthin; 4, zeaxanthin/lutein; 2, 3, 5 and 6, unknown.
[View Larger Version of this Image (20K GIF file)]

---

---

Fig. 2. Plasma capsanthin, zeaxanthin/lutein, cryptoxanthin, and -carotene concentrations in men after the periodic ingestion of paprika juice for 7 d in Study 1. Data are presented as means ± SEM (n = 4). For each carotenoid, means with different letters are significantly different (P < 0.01).
[View Larger Version of this Image (26K GIF file)]

---

Table 1. Distribution of carotenoids, -tocopherol and cholesterol in plasma lipoprotein fractions of men after periodic ingestion of paprika juice for 1 wk1 [View Table]

---

Fig. 3. Plasma capsanthin and lycopene concentrations in men after a single ingestion of paprika juice (Study 2) and tomato soup (Study 3), respectively. Values are presented as means ± SEM (n = 4). For each carotenoid, means with different letters are significantly different (P < 0.01).
[View Larger Version of this Image (17K GIF file)]

---

Distribution of carotenoids, -tocopherol and cholesterol in plasma lipoproteins. In Study 1, >70% of the hydrocarbon carotenoids (lycopene, - and -carotene) were distributed in the LDL fraction, 20-25% in the HDL fraction and <6% in the VLDL fraction (Table 1). The cis-isomers of lycopene and -carotene were distributed in each fraction similarly to the all-trans isomers (data not shown). On the other hand, ~40% of capsanthin was distributed in the LDL fraction and 40% in the HDL fraction. The distribution pattern of zeaxanthin/lutein in each lipoprotein fraction was similar to that of capsanthin. The distribution ratio of cryptoxanthin in LDL was significantly higher than those of capsanthin and zeaxanthin/lutein. -Tocopherol and cholesterol were mainly in the LDL fraction as has been reported elsewhere (Clevidence and Bieri 1993)

Pharmacokinetic parameters of capsanthin and lycopene after a single ingestion of paprika juice and tomato soup, respectively. In Study 2, the plasma capsanthin level increased following ingestion of a single serving of paprika juice (Fig. 3). Its maximal level was reached 8 h after ingestion; considerable differences in the maximal levels were found among individuals (0.10-0.29 µmol/L). However, the concentrations of the other carotenoids did not change significantly (data not shown). Two pharmacokinetic parameters, AUC_{0-74 h} and t_1/2 of capsanthin were calculated from the time course of the capsanthin concentration in plasma (Fig. 3) and are shown in Table 2. At the beginning of Study 3, the level of lycopene in the plasma of each subject was found to be <0.05 µmol/L. Plasma lycopene concentration rose significantly in the four subjects after ingestion of tomato soup, although the elevation was minimal (Fig. 3). The value of AUC_{0-72 h} for lycopene was lower than that for capsanthin (Table 2). However, the rate for elimination of lycopene from the plasma was much slower than that of capsanthin.

Table 2. Pharmacokinetic parameters of capsanthin and lycopene in blood plasma of men after single ingestions of paprika juice and tomato soup, respectively1 [View Table]

---

DISCUSSION

We previously investigated the concentration of carotenoids in plasma of 76 healthy subjects (Oshima et al. 1995). In that study, no capsanthin was identified in plasma samples. There are several possible reasons for the failure to detect capsanthin in plasma, such as the absence of capsanthin in the diet of a subject, poor absorption of dietary capsanthin or rapid excretion of absorbed capsanthin. Nevertheless, the present study clearly demonstrated that dietary capsanthin is absorbed into the body and distributed in plasma lipoproteins. Capsanthin seemed to be a suitable compound with which to assess the pharmacokinetics of xanthophylls because it was completely absent in plasma before the experiment. Capsanthin in fruits and vegetables is present mainly as an esterified form of fatty acids (Fisher and Kocis 1987). It is likely that an ester of capsanthin in paprika is hydrolyzed to a free form before accumulation in plasma because only nonesterified capsanthin was found in plasma after paprika juice ingestion.

As in the case of capsanthin, the plasma concentrations of zeaxanthin/lutein, cryptoxanthin and -carotene were elevated by the periodic ingestion of paprika juice (Fig. 2) because paprika juice contains appreciable levels of these carotenoids. White et al. (1994) investigated the effect of a single dose of -carotene or canthaxanthin and their combined dose on the concentration of carotenoids in human plasma and found that a combined dose reduced the serum canthaxanthin level by ~40%. Yet, it was reported that the ingestion of a large amount of -carotene had no effect on the plasma lycopene concentration (Ribaya-Mercado et al. 1995).

The pharmacokinetic parameters of capsanthin and lycopene obtained after a single ingestion of paprika juice and tomato soup, respectively (Table 2) indicate that capsanthin disappears from plasma much more rapidly than lycopene although more capsanthin is transported into plasma lipoproteins. Stahl and Sies (1992) showed that the lycopene concentration in human plasma was increased by the consumption of heat-processed tomato juice. We have already reported that repeated ingestion of unheated tomato juice also increases the plasma lycopene level (Sakamoto et al. 1994). Rock et al. (1992) indicated that the t_1/2 of lycopene in plasma was 11-33 d in the case of subjects exposed to a low carotenoid diet for 13 wk. The mean t_1/2 of lycopene in this experiment (~9 d) is somewhat shorter than that reported by Rock et al. (1992). However, we should emphasize that the t_1/2 of capsanthin in human plasma is much shorter than that of lycopene. This polar carotenoid may be metabolized faster than lycopene in the human body.

Clevidence and Bieri (1993) as well as Romanchik et al. (1995) showed that the HDL fraction of plasma accumulates more xanthophylls than hydrocarbon carotenoids. Our results confirm that xanthophylls, including capsanthin, are distributed to HDL in larger amounts than to LDL compared with hydrocarbon carotenoids. It is likely that nonpolar carotenoids tend to be localized in the lipophilic center of the lipoprotein consisting of triacylglycerols and cholesteryl esters. Xanthophylls are polar carotenoids; thus they are likely to be localized at the polar surface of lipoprotein consisting of phospholipids and apoprotein. HDL is rich in phospholipid and apoprotein and therefore may be liable to accumulate xanthophylls. Xanthophylls can act as antioxidants against free radical attack and exposure to singlet oxygen in plasma lipoproteins (Boey et al. 1992, Ojima et al. 1993). Thus, dietary xanthophylls seem to participate in the primary defense of HDL against oxidative attack in the bloodstream and arterial wall. Intake of capsanthin may be helpful for increasing the antioxidant defense of this plasma lipoprotein.

In conclusion, dietary capsanthin is absorbed and accumulated in appreciable amounts in human plasma lipoproteins. The distribution of capsanthin in each lipoprotein fraction and clearance rate from plasma were different from those of lycopene, a typical hydrocarbon carotenoid. Results of this study justify further studies on the physiological function of capsanthin and other xanthophylls of dietary origin.

FOOTNOTES

Manuscript received 4 December 1996. Initial reviews completed 28 January 1997. Revision accepted 5 May 1997.

LITERATURE CITED

• Blot W. J., Li J.-Y., Taylor P. R., Guo W., Dawsey S., Wang G.-O., Yang C. S., Zheng S.-F., Gail M., Li G.-Y., Yu Y., Liu B., Tangrea J., Sun Y., Liu F., Fraumeni J. F. Jr., Zhang Y.-H., Li B. Nutrition intervention trials in Linxian, China: supplementation with specific vitamin/mineral combinations, cancer incidence and disease-specific mortality in the general population. J. Natl. Cancer Inst. 1993; 85:1483-1492 [Abstract/Free Full Text]
• Boey P. L., Nagao A., Terao J., Tanaka K., Suzuki T., Takama K. Antioxidant activity of xanthophylls on peroxyl radical-mediated phospholipid peroxidation. Biochim. Biophys. Acta 1992; 1126:178-184
• [Medline] Clevidence B. A., Bieri J. G. Association of carotenoids with human plasma lipoproteins. Methods Enzymol. 1993; 214:33-46 [Medline]
• Fisher C., Kocis J. A. Separation of paprika pigments by HPLC. J. Agric. Food Chem. 1987; 35:55-57
• Gaziano, J. M. & Hennekens, C. H. (1993) The role of beta-carotene in the prevention of cardiovascular disease. Carotenoids in human health. In: Ann. Rev. N.Y. Acad. Sci. (Canfield, L. M., Krinsky, N. I. & Olson, J. A., eds.), 691: 148-155.
• Goldstein, J. L., Basu, S. K. & Brown, M. S. (1983) Receptor-mediated endocytosis of low-density lipoprotein in cultured cells, Methods Enzymol. 98: 241-260.
• Heinonen O. P., Albanes D. The effect of vitamin E and beta-carotene on the incidence of lung cancer and other cancers in male smokers. N. Engl. J. Med. 1994; 330:1029-1035
• [Abstract/Free Full Text] Hennekens C. H., Buring J. E., Manson J. E., Stampfer M., Rosner B., Cook N. R., Belanger C., LaMotte F., Gaziano J. M., Ridker P. M., Willett W., Peto R. Lack of effect of long-term supplementation with beta carotene on the incidence of malignant neoplasms and cardiovascular disease. N. Engl. J. Med. 1996; 334:1145-1149 [Abstract/Free Full Text]
• Kaplan L. A., Lau J. M., Stein E. A. Carotenoid composition, concentrations, and relationships in various human organs. Clin. Physiol. Biochem. 1990; 8:1-10
• Khachik F., Beecher G. R., Smith J. C. Lutein, lycopene, and their oxidative metabolites in chemoprevention of cancer. J. Cell. Biochem. 1995; 22:236s-246s
• Levy J., Bosin E., Feldman B., Giat Y., Miinster A., Danilenko M., Sharoni Y. Lycopene is a more potent inhibitor of human cancer cell proliferation than either -carotene or -carotene. Nutr. Cancer. 1995; 24:257-267 [Medline]
• Manago, M.,Tamai, H.,Ogihara,T., Mino M. Distribution of circulating -carotene in human plasma lipoproteins. J. Nutr. Sci. Vitaminol. 1992; 38:405-414
• Mathews-Roth M. M., Welankiwar S., Sehgal P. K., Lausen N.C.G., Russett M., Krinsky N. I. Distribution of [¹⁴C]canthaxanthin and [¹⁴C]lycopene in rats and monkeys. J. Nutr. 1990; 120:1205-1213
• Murakoshi M., Nishino H., Satomi Y., Takayasu J., Hasegawa T., Tokuda H., Iwashima A., Okuzumi J., Okabe H., Kitano H., Iwasaki R. Potent preventive action of -carotene against carcinogenesis: spontaneous liver carcinogenesis and promoting stage on lung and skin carcinogenesis in mice are suppressed more effectively by -carotene than by -carotene. Cancer Res. 1992; 52:6583-6587 [Abstract/Free Full Text]
• Ojima F., Sakamoto H., Ishiguro Y., Terao J. Consumption of carotenoids in photosensitized oxidation of human plasma and plasma low-density lipoprotein. Free Radical Biol. Med. 1993; 15:377-384 [Medline]
• Omenn G. S., Goodman G. E., Thornquist M. D., Balmes J., Cullen M. R., Glass A., Keogh J. P., Meyskens F. L., Valanis B., Williams J. H., Barnhart S., Hammar S. Effects of a combination of beta carotene and vitamin A on lung cancer and cardiovascular disease. N. Engl. J. Med. 1996; 334:1150-1155 [Abstract/Free Full Text]
• Oshima S., Ojima F., Sakamoto H., Ishiguro Y. Factors affecting carotenoid levels in human plasma. J. Jpn. Soc. Nutr. Food Sci. 1995; 48:365-369
• Peto R., Buckley J. D., Sporn M. B. Can dietary beta-carotene materially reduce human cancer rates? Nature (Lond.) 1981; 290:201-208 [Medline]
• Phillips, G. M. & Taylor, P. J. (1973) Numerical differentiation and integration. In: Theory and Applications of Numerical Analysis (Philips, G. M. & Taylor, P. J., eds.), pp. 120-153, Academic Press, New York, NY.
• Pung A., Rundhaug J. E., Yoshizawa C. N., Bertram J. S. . -Carotene and canthaxanthin inhibit chemically and physically induced neoplastic trasformation in 10T1/2 cells. Carcinogenesis 1988; 9:1533-1539 [Abstract/Free Full Text]
• Ribaya-Mercado J. D., Garmyn M., Gilchrest B. A., Russell R. M. Skin lycopene is destroyed preferentially over -carotene during ultraviolet irradiation in humans. J. Nutr. 1995; 125:1854-1859
• Rock C. L., Swendseid M. E., Jacob R. A., Mckee R. W. Plasma carotenoid levels in human subjects fed a low carotenoid diet. J. Nutr. 1992; 122:96-100
• Romanchik J. E., Morel D. W., Harrison E. H. Distributions of carotenoids and -tocopherol do not change when human plasma is incubated in vitro. J. Nutr. 1995; 125:2610-2617
• Rowland M., Benet L. Z., Graham G. C. Clearance concepts in pharmacokinetics. J. Pharmacokin. Biopharm. 1973; 1:123-136 [Medline]
• Sakamoto H., Mori H., Ojima F., Ishiguro Y., Arimoto S., Imae Y., Nanba T., Ogawa M., Fukuba H. Elevation of serum carotenoids after continual ingestion of tomato juice. J. Jpn. Soc. Nutr. Food Sci. 1994; 47:93-99
• Stahl W., Sies H. Uptake of lycopene and its geometrical isomers is greater from heat-processed than from unprocessed tomato juice in humans. J. Nutr. 1992; 122:2161-2166
• Steel, R.G.D. & Torrie, J. H. (1982) Principles and Procedures of Satatistics: A Biometrical Approach. McGraw-Hill International Book Company, Auckland, New Zealand.
• Tanaka T., Morishita Y., Suzui M., Kojima T., Okumura A., Mori H. Chemoprevention of mouse urinary bladder carcinogenesis by the naturally occurring carotenoid astaxanthin. Carcinogenesis 1994; 15:15-19 [Abstract/Free Full Text]
• van Poppel, G. (1993) Carotenoids and cancer: an update with emphasis on human intervention studies. Eur. J. Cancer 29A: 1335-1344.
• White W. S., Stacewicz-Sapuntzakis M., Erdman J. W., Bowen P. E. Pharmacokinetics of -carotene and canthaxanthin after ingestion of individual and combined doses by human subjects. J. Am. Coll. Nutr. 1994; 13:665-671 [Abstract]
• Zar, J. H. (1974) Biostatistical Analysis. Prentice-Hall, Englewood Cliffs, NJ.
• Ziegler R. G. A view of the epidemiological evidence that carotenoids reduce the risk of cancer. J. Nutr. 1988; 119:116-122

0022-3166/97 $3.00 ©1997 American Society for Nutritional Sciences