No abstract

Iron deficiency is a major world health problem, that is, to a great extent, caused by poor iron absorption from the diet. Several dietary factors can influence this absorption. Absorption enhancing factors are ascorbic acid and meat, fish and poultry; inhibiting factors are plant components in vegetables, tea and coffee (e.g., polyphenols, phytates), and calcium. After identifying these factors their individual impact on iron absorption is described. Specific attention was paid to the effects of tea on iron absorption. We propose a calculation model that predicts iron absorption from a meal. Using this model we calculated the iron absorption from daily menus with varying amounts of enhancers and inhibitors. From these calculations we conclude that the presence of sufficient amounts of iron absorption enhancers (ascorbic acid, meat, fish, poultry, as present in most industrialized countries) overcomes inhibition of iron absorption from even large amounts of tea. In individuals with low intakes of heme iron, low intakes of enhancing factors and/or high intakes of inhibitors, iron absorption may be an issue. Depletion of iron stores enhances iron absorption, but this effect is not adequate to compensate for the inhibition of iron absorption in such an inadequate dietary situation. For subjects at risk of iron deficiency, the following recommendations are made. Increase heme-iron intake (this form of dietary iron present in meat fish and poultry is hardly influenced by other dietary factors with respect to its absorption); increase meal-time ascorbic acid intake; fortify foods with iron. Recommendations with respect to tea consumption (when in a critical group) include: consume tea between meals instead of during the meal; simultaneously consume ascorbic acid and/or meat, fish and poultry.

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), ␣-plus ␤-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, ␣-and ␤-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 lowfat spread and 23% increase with the high-fat spread) or ␣-and ␤-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 ␣-and ␤-carotene requires a limited amount of fat whereas the amount of fat required for optimal intestinal uptake of lutein esters is higher.

Objective: To investigate the effect of black and green tea consumption, with and without milk, on the plasma antioxidant activity in humans. Design: In a complete cross-over design, 21 healthy volunteers (10 male, 11 female) received a single dose of black tea, green tea (2 g tea solids in 300 ml water) or water with or without milk. Blood samples were obtained at baseline and at several time points up to 2 h post-tea drinking. Plasma was analysed for total catechins and antioxidant activity, using the ferric reducing ability of plasma (FRAP) assay. Results: Consumption of black tea resulted in a signi®cant increase in plasma antioxidant activity reaching maximal levels at about 60 min. A larger increase was observed after consumption of green tea. As anticipated from the higher catechin concentration in green tea, the rise in plasma total catechins was signi®cantly higher after consumption of green tea when compared to black tea. Addition of milk to black or green tea did not affect the observed increases in plasma antioxidant activity. Conclusions: Consumption of a single dose of black or green tea induces a signi®cant rise in plasma antioxidant activity in vivo. Addition of milk to tea does not abolish this increase. Whether the observed increases in plasma antioxidant activity after a single dose of tea prevent in vivo oxidative damage remains to be established.

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 mmol/l (13%) after ingestion of green tea and 0.10 mmol/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 t 1a2 4.8 h (5%) for green tea and t 1a2 6.9 h (8%) for black tea. Addition of milk to black tea (100 ml in 600 ml) did not signi®cantly affect the blood catechin levels (areas under the curves (mean (CVM) of 0.53 h. mmol/l (11%) vs 0.60 h. mmol/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.