Addition of milk does not affect the absorption of flavonols from tea in man.

Tea is a major source of flavonols, a subclass of antioxidant flavonoids present in plant foods which potentially are beneficial to human health. Milk added to tea, a frequent habit in the United Kingdom, could inhibit absorption of tea flavonoids, because proteins can bind flavonoids effectively. Eighteen healthy volunteers each consumed two out of four supplements during three days: black tea, black tea with milk, green tea and water. A cup of the supplement was consumed every 2 hours each day for a total of 8 cups a day. The supplements provided about 100 micromol quercetin glycosides and about 60 - 70 micromol kaempferol glycosides. Addition of milk to black tea (15 ml milk to 135 ml tea) did not change the area under the curve of the plasma concentration-time curve of quercetin or kaempferol. Plasma concentrations reached were about 50 nM quercetin and 30 - 45 nM kaempferol. We conclude that flavonols are absorbed from tea and that their bioavailability is not affected by addition of milk.

Amount of fat in the diet affects bioavailability of lutein esters but not of alpha-carotene, beta-carotene, and vitamin E in humans.

BACKGROUND: Fat-soluble vitamin E and carotenoids are regarded as being protective against chronic diseases. Little is known about the effect of dietary fat on the bioavailability of these compounds. OBJECTIVE: The objective of this study was to assess the effect of the amount of dietary fat on plasma concentrations of vitamin E and carotenoids after supplementation with these compounds. DESIGN: During two 7-d periods, 4 groups of 14-15 volunteers received daily, with a low-fat hot meal, 1 of 4 different supplements: vitamin E (50 mg), alpha- plus beta-carotene (8 mg), lutein esters (8 mg lutein), or placebo. The supplements were provided in a low- or high-fat spread supplied in random sequence during either of the 2 experimental periods. RESULTS: As anticipated, plasma concentrations of vitamin E, alpha- and beta-carotene, and lutein were significantly higher in the supplemented groups than in the placebo group. The amount of dietary fat consumed with the hot meal (3 or 36 g) did not affect the increases in plasma concentrations of vitamin E (20% increase with the low-fat spread and 23% increase with the high-fat spread) or alpha- and beta-carotene (315% and 139% with the low-fat spread and 226% and 108% with the high-fat spread). The plasma lutein response was higher when lutein esters were consumed with the high-fat spread (207% increase) than with the low-fat spread (88% increase). CONCLUSION: Optimal uptake of vitamin E and alpha- and beta-carotene requires a limited amount of fat whereas the amount of fat required for optimal intestinal uptake of lutein esters is higher. 2000;71:-93.

Comparison of the bioavailability of natural palm oil carotenoids and synthetic beta-carotene in humans.

Palm oil carotenoids are a mixture of alpha- and beta-carotenes, which are used as food colorants. They may also be applied as a functional food ingredient because of the provitamin A activity of alpha- and beta-carotenes and their proposed beneficial roles in the prevention of chronic diseases. This paper discusses the results of an incomplete balanced crossover study with 69 healthy adult volunteers to compare palm oil carotenoids with synthetic beta-carotene in their efficacies to increase plasma levels of carotenoids. Four days of supplementation with natural palm oil carotenoids (7.6 mg/day of alpha-carotene, 11.9 mg/day of all-trans-beta-carotene, 7.5 mg/day of cis-beta-carotene) or synthetic beta-carotene (23.8 mg/day of all-trans-beta-carotene, 4.4 mg/day of cis-beta-carotene), added to a mixed meal, resulted in significant increases in plasma levels of the supplied carotenoids as compared to consumption of a low-carotenoid meal (i.e., 7.2-fold increase in alpha-carotene and 3.5-fold increase in all-trans-beta-carotene following palm oil carotenoids; 6.9-fold increase in all-trans beta-carotene following synthetic beta-carotene). As the carotenoid content differed between the treatments, the relative plasma responses were calculated per milligram of beta-carotene intake. These were similar for the two supplements, suggesting that the presence of alpha-carotene does not affect the bioavailability of beta-carotene from palm oil. It was concluded that 4 days of supplementation with palm oil carotenoids or synthetic beta-carotene improves the plasma beta-carotene status substantially, whereas alpha-carotene is additionally delivered by the palm oil supplement.

beta-carotene does not change markers of enzymatic and nonenzymatic antioxidant activity in human blood.

In vitamin A-replete populations, increased concentrations of serum carotenoids have been associated with a decreased risk of degenerative diseases. The mechanism of action of carotenoids in determining antioxidant activity is largely unknown. The aim of the study was to examine the effect of carotenoid supplementation and spinach intake on erythrocyte enzyme antioxidant activities, serum or plasma nonenzymatic antioxidant concentrations, and concentrations of oxidatively damaged amino acids in plasma. Subjects received for 3 wk a basic diet (n = 10), a basic diet with a carotenoid supplement (n = 12) or with a spinach product (n = 12 per group), i.e., whole-leaf, minced, liquefied or liquefied spinach plus added dietary fiber. After 3 wk of dietary intervention, changes in serum or plasma concentrations of ascorbic acid, alpha-tocopherol, FRAP (ferric reducing ability of plasma) and uric acid and erythrocyte enzyme activities were assessed, and differences among experimental groups were tested. Consumption of spinach resulted in greater (P < 0.01) erythrocyte glutathione reductase activity and lower (P < 0.05) erythrocyte catalase activity and serum alpha-tocopherol concentration compared with the control group. Consumption of the carotenoid supplement led to lower alpha-tocopherol responses (P = 0.02) compared with the basic diet only. Our data suggest that the short-term changes in erythrocyte glutathione reductase activity and serum alpha-tocopherol concentration can be attributed to an increased carotenoid (lutein and zeaxanthin) intake, but beta-carotene is unlikely to be a causative factor. Lower erythrocyte catalase activity after intervention with spinach products may be related to other constituents in spinach such as flavonoids.

Bioavailability of lutein from vegetables is 5 times higher than that of beta-carotene.

BACKGROUND: To gain more insight into the relation between vegetable consumption and the risk of chronic diseases, it is important to determine the bioavailability of carotenoids from vegetables and the effect of vegetable consumption on selected biomarkers of chronic diseases. OBJECTIVE: To assess the bioavailability of beta-carotene and lutein from vegetables and the effect of increased vegetable consumption on the ex vivo oxidizability of LDL. DESIGN: Over 4 wk, 22 healthy adult subjects consumed a high-vegetable diet (490 g/d), 22 consumed a low-vegetable diet (130 g/d), and 10 consumed a low-vegetable diet supplemented with pure beta-carotene (6 mg/d) and lutein (9 mg/d). RESULTS: Plasma concentrations of vitamin C and carotenoids (ie, alpha-carotene, beta-carotene, lutein, zeaxanthin, and beta-cryptoxanthin) were significantly higher after the high-vegetable diet than after the low-vegetable diet. In addition to an increase in plasma beta-carotene and lutein, the pure carotenoid-supplemented diet induced a significant decrease in plasma lycopene concentration of -0.11 micromol/L (95% CI: -0.21, -0.0061). The responses of plasma beta-carotene and lutein to the high-vegetable diet were 14% and 67%, respectively, of those to the pure carotenoid- supplemented diet. Conversion of beta-carotene to retinol may have attenuated its plasma response compared with that of lutein. There was no significant effect on the resistance of LDL to oxidation ex vivo. CONCLUSIONS: Increased vegetable consumption enhances plasma vitamin C and carotenoid concentrations, but not resistance of LDL to oxidation. The relative bioavailability of lutein from vegetables is higher than that of beta-carotene.

Dietary folate from vegetables and citrus fruit decreases plasma homocysteine concentrations in humans in a dietary controlled trial.

Elevated total plasma homocysteine (tHcy) concentrations are considered a risk factor for neural tube defects (NTD) and cardiovascular disease. Supplementation with folic acid decreases the risk of women having children with NTD. In both sexes, it decreases tHcy levels. We investigated the efficacy of natural dietary folate in improving folate and homocysteine status. We performed a 4-wk dietary controlled, parallel design intervention trial with 66 healthy subjects (18-45 y) divided into 3 treatment groups: the dietary folate group, the folic acid group and the placebo group. Each day each group was fed a different diet. The dietary folate group received a diet high in vegetables and citrus fruit (total folate content approximately 560 microgram) plus a placebo tablet. The folic acid group received a diet naturally low in folate (approximately 210 microgram) plus 500 microgram folic acid and placebo tablet on alternate days, i.e., 250 microgram folic acid/d. And the placebo group received the same low-folate diet as the folic acid group plus a placebo tablet. After 4 wk of intervention, folate status improved, and tHcy concentrations decreased in both the dietary folate and the folic acid groups. From the amount of additional folate (350 microgram/d) and folic acid (250 microgram/d) consumed, the relative bioavailability of dietary folate compared to folic acid was calculated to be 60-98%, depending on the endpoint used. In conclusion, increasing the consumption of vegetables and citrus fruit, both good sources of folate, will improve folate status and decrease tHcy concentrations. This may contribute to the prevention of cardiovascular disease and NTD in the general population

Plasma and lipoprotein levels of tea catechins following repeated tea consumption.

Epidemiological studies suggest that antioxidant flavonoids in tea may reduce the risk of cardiovascular disease, possibly via protection of low-density lipoproteins (LDL) against oxidation. However, the extent of absorption of tea flavonoids and their accumulation in LDL during regular consumption of tea is not clear. Therefore we investigated plasma and lipoprotein levels of catechins during tea consumption and the impact on LDL oxidizability ex vivo. Eighteen healthy adults consumed, in an incomplete balanced cross-over design, green tea, black tea, black tea with milk or water, one cup every 2 hr (eight cups/day) for three days. Blood samples were obtained in the mornings and evenings of each day. Plasma total catechin concentration was determined in all blood samples, and the distribution of catechins among lipoproteins was determined at the end of the third day (t = 60 hr). The resistance of LDL to copper-induced oxidation ex vivo was assessed before tea consumption and at t = 60 hr. Repeated tea consumption during the day rapidly increased plasma total catechin levels whereas they declined overnight when no tea was consumed. There was a gradual increase in plasma levels in the mornings (respectively, 0.08 microM vs. 0.20 microM on first and last day of black tea consumption) and evenings (respectively, 0.29 microM vs. 0.34 microM on first and last day of black tea consumption). Green tea catechins were mainly found in the protein-rich fraction of plasma (60%) and in high-density lipoproteins (23%). Although present in LDL, the concentration of catechins in LDL was not sufficient to enhance the resistance of LDL to oxidation ex vivo. Addition of milk to black tea did not affect any of the parameters measured. In conclusion, the present study shows that catechin levels in blood rapidly increase upon repeated tea consumption. The accumulation of catechins in LDL particles is not sufficient to improve the intrinsic resistance of LDL to oxidation ex vivo.

The food matrix of spinach is a limiting factor in determining the bioavailability of beta-carotene and to a lesser extent of lutein in humans.

Carotenoid bioavailability depends, amongst other factors, on the food matrix and on the type and extent of processing. To examine the effect of variously processed spinach products and of dietary fiber on serum carotenoid concentrations, subjects received, over a 3-wk period, a control diet (n = 10) or a control diet supplemented with carotenoids or one of four spinach products (n = 12 per group): whole leaf spinach with an almost intact food matrix, minced spinach with the matrix partially disrupted, enzymatically liquefied spinach in which the matrix was further disrupted and the liquefied spinach to which dietary fiber (10 g/kg wet weight) was added. Consumption of spinach significantly increased serum concentrations of all-trans-beta-carotene, cis-beta-carotene, (and consequently total beta-carotene), lutein, alpha-carotene and retinol and decreased the serum concentration of lycopene. Serum total beta-carotene responses (changes in serum concentrations from the start to the end of the intervention period) differed significantly between the whole leaf and liquefied spinach groups and between the minced and liquefied spinach groups. The lutein response did not differ among spinach groups. Addition of dietary fiber to the liquefied spinach had no effect on serum carotenoid responses. The relative bioavailability as compared to bioavailability of the carotenoid supplement for whole leaf, minced, liquefied and liquefied spinach plus added dietary fiber for beta-carotene was 5.1, 6.4, 9.5 and 9.3%, respectively, and for lutein 45, 52, 55 and 54%, respectively. We conclude that the bioavailability of lutein from spinach was higher than that of beta-carotene and that enzymatic disruption of the matrix (cell wall structure) enhanced the bioavailability of beta-carotene from whole leaf and minced spinach, but had no effect on lutein bioavailability.

Influence of feeding different vegetables on plasma levels of carotenoids, folate and vitamin C. Effect of disruption of the vegetable matrix.

Carotenoids, folate and vitamin C may contribute to the observed beneficial effects of increased vegetable intake. Currently, knowledge on the bioavailability of these compounds from vegetables is limited. We compared the efficacy of different vegetables, at the same level of intake (i.e. 300 g/d), in increasing plasma levels of carotenoids, folate and vitamin C and we investigated if disruption of the vegetable matrix would enhance the bioavailability of these micronutrients. In an incomplete block design, sixty-nine volunteers consumed a control meal without vegetables and three out of four vegetable meals (i.e. broccoli, green peas, whole leaf spinach, chopped spinach; containing between 1.7 and 24.6 mg beta-carotene, 3.8 and 26 mg lutein, 0.22 and 0.60 mg folate and 26 and 93 mg vitamin C) or a meal supplemented with synthetic beta-carotene (33.3 mg). Meals were consumed for 4 d and fasting blood samples were taken at the end of each period. Consumption of the spinach-supplemented meal did not affect plasma levels of beta-carotene, although the beta-carotene content was 10-fold those of broccoli and green peas, which induced significant increases in plasma beta-carotene levels (28 (95% CI 6.4, 55)% and 26 (95% CI 2.6, 54)% respectively). The beta-carotene-supplemented meal increased plasma concentrations of beta-carotene effectively (517 (95% CI 409, 648)%). All vegetable meals increased the plasma concentrations of lutein and vitamin C significantly. Broccoli and green peas were, when expressed per mg carotenoid consumed, also more effective sources of lutein than spinach. A significant increase in plasma folate concentration was found only after consumption of the spinach-supplemented meal, which provided the highest level of folate. Disruption of the spinach matrix increased the plasma responses to both lutein (14 (95% CI 3.7, 25)%) and folate (10 (95% CI 2.2, 18)%), whereas it did not affect the response to beta-carotene. We conclude that the bioavailabilities of beta-carotene and lutein vary substantially among different vegetables and that the bioavailabilities of lutein and folate from spinach can be improved by disruption of the vegetable matrix.

Bioavailability of catechins from tea: the effect of milk.

OBJECTIVES: To assess the blood concentration of catechins following green or black tea ingestion and the effect of addition of milk to black tea. DESIGN: Twelve volunteers received a single dose of green tea, black tea and black tea with milk in a randomized cross-over design with one-week intervals. Blood samples were drawn before and up to eight hours after tea consumption. SETTING: The study was performed at the Unilever Research Vlaardingen in The Netherlands. SUBJECTS: Twelve healthy adult volunteers (7 females, 5 males) participated in the study. They were recruited among employees of Unilever Research Vlaardingen. INTERVENTIONS: Green tea, black tea and black tea with semi-skimmed milk (3 g tea solids each). RESULTS: Consumption of green tea (0.9 g total catechins) or black tea (0.3 g total catechins) resulted in a rapid increase of catechin levels in blood with an average maximum change from baseline (CVM) of 0.46 micromol/l (13%) after ingestion of green tea and 0.10 micromol/l (13%) in case of black tea. These maximum changes were reached after (mean (s.e.m.)) t=2.3 h (0.2) and t=2.2 h (0.2) for green and black tea respectively. Blood levels rapidly declined with an elimination rate (mean (CVM)) of t1/2=4.8 h (5%) for green tea and t1/2=6.9 h (8%) for black tea. Addition of milk to black tea (100 ml in 600 ml) did not significantly affect the blood catechin levels (areas under the curves (mean (CVM) of 0.53 h. micromol/l (11%) vs 0.60 h. micromol/l (9%) for black tea and black tea with milk respectively. CONCLUSION: Catechins from green tea and black tea are rapidly absorbed and milk does not impair the bioavailability of tea catechins.

Antioxidant fortified margarine increases the antioxidant status.

OBJECTIVE: To assess the effect of supplementation with an antioxidant fortified margarine on the body's antioxidant status and on parameters of oxidative damage to lipids. DESIGN: Single blind, placebo controlled trial, two treatment groups balanced for sex, age and Quetelet Index. SETTING: Unilever Research Laboratorium, The Netherlands. SUBJECTS: Thirty-one healthy adult volunteers accomplished the study. Volunteers were recruited among inhabitants of the surrounding area of the research laboratory. INTERVENTIONS: Volunteers consumed during the four weeks either 15 g/d of an antioxidant fortified margarine (providing 121 mg vitamin C, 31 mg vitamin E, 2.7 mg alpha-carotene and 5.3 mg beta-carotene) or an ordinary margarine. Fasting blood samples were taken before and at the end of the study. RESULTS: Consumption of the antioxidant fortified margarine significantly increased the levels of the supplied antioxidants in plasma and LDL as compared to the changes found after consumption of the control margarine, with the largest increases found in LDL levels of alpha-carotene (15.5-fold increase, 95% CI: 8.4-27.8-fold) and beta-carotene (4.3-fold increase, 95% CI: 2.2-7.9-fold). This increased antioxidant status in the antioxidant fortified margarine group resulted in a significantly increased total antioxidant activity of LDL and resistance of LDL to oxidation (lag time and rate of oxidation) as compared to baseline but not in comparison to the changes found in the control group. CONCLUSION: Consumption of moderate doses of vitamin E, vitamin C, alpha-carotene and beta-carotene, supplied in a full-fat margarine and consumed as part of a normal diet, effectively increases the blood levels of these antioxidants.

Consumption of green or black tea does not increase resistance of low-density lipoprotein to oxidation in humans.

Epidemiologic studies indicated that tea consumption reduces the risk of cardiovascular disease. We assessed the effect of green or black tea consumption on resistance of low-density lipoprotein (LDL) to oxidation ex vivo and on serum lipid concentrations in healthy volunteers. In a 4-wk parallel comparison trial, 45 volunteers consumed 900 mL (6 cups) mineral water, green tea, or black tea/d. Blood samples drawn while subjects were fasting were obtained before and after the study. The effect on resistance of subsequently isolated LDL to oxidation of adding green or black tea extract to plasma was investigated in an in vitro experiment. Consumption of 900 mL (6 cups) green or black tea/d did not affect serum lipid concentrations, resistance of LDL to oxidation, or markers of oxidative damage to lipids in vivo, although consumption of green tea slightly increased total antioxidant activity of plasma. The in vitro experiment showed that resistance of isolated LDL to oxidation increased only after incubation of plasma with very high amounts of green or black tea. These amounts, when converted to tea catechin concentrations, were much higher than those expected in vivo. We conclude that daily consumption of 900 mL (6 cups) green or black tea/d for 4 wk had no effect on serum lipid concentrations or resistance of LDL to oxidation ex vivo. Future research should focus on mechanisms by which tea flavonoids may reduce the risk of cardiovascular disease other than by increasing the intrinsic antioxidant status of LDL.

Folate intake in Europe: recommended, actual and desired intake.

OBJECTIVES: To evaluate possible inconsistencies between recommended, actual and desired folate intake in European adult populations. DESIGN: Review of dietary recommendations, of food consumption surveys, and of intervention and observational studies relating folate intake to the risk of neural tube defects and plasma homocysteine levels. RESULTS: In Europe, mean dietary folate intake in adults is 291 micrograms/d (range 197-326) for men and 247 micrograms/d (range 168-320) for women. The recommended intakes vary between 200-300 micrograms/d (men) and 170-300 micrograms/d (women). However, women with a previous pregnancy affected by a neural tube defect (NTD), are recommended to take 4000 micrograms/d of supplemental folic acid when planning a subsequent pregnancy. For those without a history of NTD, the use of 400 micrograms/d of supplemental folic acid is the best option to prevent the occurrence of NTDs. A daily dose of 650 micrograms supplemental folic acid normalises elevated plasma homocysteine levels, which is a risk factor for cardiovascular diseases. A dietary folate intake of at least 350 micrograms/d is desired to prevent an increase in plasma homocysteine levels of the adult population in general. CONCLUSIONS: Mean dietary folate intake in Europe is in line with recommendations, but the desired dietary intake of > 350 micrograms/d is only reached by a small part of studied European populations. It is considered unethical to investigate whether supplements with a dose lower than 400 micrograms/d of folic acid are also protective against NTDs. However, research to establish the lowest effective dose of dietary folate/supplemental folic acid to optimise homocysteine levels and research on the bioavailability of folate is required. This will enable the choice of a strategy to achieve desired folate intakes in the general population. In the meantime, consumption of plant foods like vegetables, fruits, and cereals should be stimulated to reach the desired level of 350 micrograms of dietary folate per day.

Sucrose polyester and plasma carotenoid concentrations in healthy subjects.

A double-blind, placebo-controlled crossover study of the effects of the nonabsorbable fat analogue sucrose polyester (SPE; 12.4 g/d) on plasma concentrations of five different carotenoids and vitamin E in 21 volunteers, and a double-blind, placebo-controlled parallel comparison study in 53 subjects of the effect of 3 g SPE/d on plasma concentrations of two different carotenoids were undertaken. SPE-containing margarine added to the main meal was used. SPE (12.4 g/d) reduced plasma of beta-carotene concentrations by 0.13 mumol/L (34%, P = 0.0001) and concentrations of lycopene by 0.14 mumol/L (52%, P = 0.0001). Smaller but significant reductions were found for plasma concentrations of beta-cryptoxanthin, lutein, zeaxanthin, and vitamin E. SPE (3 g/d) reduced plasma concentrations of beta-carotene by 0.094 mumol/L (20% P = 0.0001) and concentrations of lycopene by 0.12 mumol/L (38%, P = 0.0001). Even at low doses, SPE strongly reduces plasma carotenoid concentrations. This finding merits careful consideration in assessing the long-term health effects of SPE-containing consumer foods.