Recommendations for vitamin A intake are based on maintaining liver stores of >or= 0·070 μmol/g, which is sufficient to maintain normal vision. We propose that higher levels may be required to ...maintain normal immune function. To test this hypothesis, we conducted an 8-week residential study among thirty-six healthy Bangladeshi men with low vitamin A stores. Subjects were randomised to receive vitamin A (240 mg in four doses) or placebo during study weeks 2 and 3. Vitamin A stores were estimated by isotopic dilution at week 8. Total T-cells, the naive T-cells:memory T-cells ratio and mitogen-induced lymphocyte proliferation were positively and significantly correlated with vitamin A stores (P < 0·05). Mitogen-stimulated IL-2, IL-4 and TNFα increased significantly (P < 0·05) in the vitamin A but not placebo group after supplementation, while IL-10 production was significantly and negatively correlated with vitamin A stores (P < 0·05). Segmented linear regression analysis revealed that naive T-cell counts and T-cell blastogenesis were positively associated with vitamin A stores above but not below 0·070 μmol/g liver. These data show that increasing vitamin A stores above the level that maintains normal vision enhances some measures of T-cell-mediated immunity, suggesting a difference in requirements for maintaining vision and immune function.
Background: It is not known whether daily consumption of vitamin A-containing foods is efficacious for treating nightblindness. Objective: We assessed the effect of supplementation with vitamin A ...from food or synthetic sources on dark adaptation and plasma retinol concentrations in nightblind pregnant Nepali women. Design: Nightblind pregnant women were randomly assigned to 1 of 6 treatment groups to receive 6 d/wk for 6 wk either 850 microgram retinol equivalents/d as retinyl palmitate, vitamin A-fortified rice, goat liver, amaranth leaves, or carrots or 2000 microgram retinol equivalents/d as retinyl palmitate. Dark adaptation was assessed weekly by using the pupillary threshold (PT) test; plasma retinol concentrations were measured before and after the intervention. These outcomes were also assessed in a comparison group of nonnightblind pregnant women. Results: In the nightblind women, the mean PT improved significantly (P < 0.0001) from -0.71 +/- 0.04 to -1.42 +/- 0.02 log cd/m2, and the final mean PT did not differ significantly from that in the nonnightblind women (-1.43 +/- 0.04; P = 0.55). Improvement in dark adaptation was greater in the liver group than in the vitamin A-fortified rice group (P < 0.02). Plasma retinol concentrations increased significantly (P < 0.0001) from 0.95 +/- 0.05 to 1.07 +/- 0.05 micromol/L. The plasma retinol response was greater in the higher-dose capsule and liver groups than in the vegetable groups and significantly greater in the liver group than in the vitamin A-fortified rice group (both: P < 0.05). Conclusion: Improvement in dark adaptation did not differ significantly between women who received vitamin A as liver, amaranth leaves, carrots, or retinyl palmitate.
Current recommendations for vitamin A intake and liver stores (0.07 μmol/g) are based on maintaining normal vision. Higher levels may be required for maintaining normal immune function. The objective ...of this study was to assess the relationship between total body vitamin A stores in adult men and measures of adaptive immune function. We conducted an 8-wk residential study among 36 healthy Bangladeshi men with low vitamin A stores. Subjects received a standard diet and were randomized in a double-blind fashion to receive vitamin A (240 mg) or placebo during wk 2 and 3. Subjects received Yellow Fever Virus (YFV) and tetanus toxoid (TT) vaccines during wk 5. Vitamin A stores were estimated by isotopic dilution during wk 8. Vaccine-specific lymphocyte proliferation, cytokine production, and serum antibody responses were evaluated before and after vaccination. Vitamin A supplementation increased YFV- and TT-specific lymphocyte proliferation and YFV-specific interleukin (IL)-5, IL-10, and tumor necrosis factor-α production but inhibited development of a TT-specific IL-10 response. Both groups developed protective antibody responses to both vaccines. Some responses correlated positively with vitamin A stores. These findings indicate that the currently recommended vitamin A intake is sufficient to sustain a protective response to YFV and TT vaccination. However, YFV-specific lymphocyte proliferation, some cytokine responses, and neutralizing antibody were positively associated with liver vitamin A stores > 0.084 μmol/g. Such increases may enhance vaccine protection but raise the question of whether immune-mediated chronic diseases may by exacerbated by high-level dietary vitamin A.
β-Carotene is an important dietary source of vitamin A for humans. However, the bioavailability and vitamin A equivalency of β-carotene are highly variable and can be affected by food- and ...diet-related factors, including the food matrix, food-processing techniques, size of the dose of β-carotene, and the amounts of dietary fat, fiber, vitamin A, and other carotenoids in the diet as well as by characteristics of the target population, such as vitamin A status, nutrient deficiencies, gut integrity, and genetic polymorphisms associated with β-carotene metabolism. The absorption of β-carotene from plant sources ranges from 5% to 65% in humans. Vitamin A equivalency ratios for β-carotene to vitamin A from plant sources range from 3.8:1 to 28:1, by weight. Vitamin A equivalency ratios for β-carotene from biofortified Golden Rice or biofortified maize are 3.8:1 and 6.5:1, respectively, and are lower than ratios for vegetables that have more complex food matrices (10:1 to 28:1). The vitamin A equivalency of β-carotene is likely to be context-specific and dependent on specific food- and diet-related factors and the health, nutritional, and genetic characteristics of human populations. Although the vitamin A equivalency of β-carotene is highly variable, the provision of vegetable and fruit sources of β-carotene has significantly increased vitamin A status in women and children in community settings in developing countries; these results support the inclusion of dietary interventions with plant sources of β-carotene as a strategy for increasing vitamin A status in populations at risk of deficiency.
β-Carotene is an important dietary source of vitamin A for humans. However, the bioavailability and vitamin A equivalency of β-carotene are highly variable and can be affected by food- and ...diet-related factors, including the food matrix, food-processing techniques, size of the dose of β-carotene, and the amounts of dietary fat, fiber, vitamin A, and other carotenoids in the diet as well as by characteristics of the target population, such as vitamin A status, nutrient deficiencies, gut integrity, and genetic polymorphisms associated with β-carotene metabolism. The absorption of β-carotene from plant sources ranges from 5% to 65% in humans. Vitamin A equivalency ratios for β-carotene to vitamin A from plant sources range from 3.8:1 to 28:1, by weight. Vitamin A equivalency ratios for β-carotene from biofortified Golden Rice or biofortified maize are 3.8:1 and 6.5:1, respectively, and are lower than ratios for vegetables that have more complex food matrices (10:1 to 28:1). The vitamin A equivalency of β-carotene is likely to be context-specific and dependent on specific food- and diet-related factors and the health, nutritional, and genetic characteristics of human populations. Although the vitamin A equivalency of β-carotene is highly variable, the provision of vegetable and fruit sources of β-carotene has significantly increased vitamin A status in women and children in community settings in developing countries; these results support the inclusion of dietary interventions with plant sources of β-carotene as a strategy for increasing vitamin A status in populations at risk of deficiency. PUBLICATION ABSTRACT
Background:Nightblindness affects 16-52% of pregnant women in areas of Nepal and in some cases persists after vitamin A treatment. Iron and riboflavin affect vitamin A utilization and photoreceptor ...function, respectively, and pilot data in the study population showed a high prevalence of iron and riboflavin deficiencies. Objective:The objective was to assess the effect of supplemental iron and riboflavin on pupillary threshold (PT) and plasma retinol in nightblind, pregnant Nepali women given vitamin A-fortified rice. Design:Nightblind pregnant women were randomly assigned to receive, 6 d/wk under supervision for 6 wk, a vitamin A-fortified rice curry dish providing 850 μg retinal activity equivalents/d with either a 30-mg Fe and 6-mg riboflavin (FeR + VA) capsule or a placebo control (VA only) capsule. Hemoglobin, erythrocyte riboflavin, and plasma ferritin and retinol were measured before and after the intervention. Dark adaptation was assessed by PT score. Results:Women who were iron deficient at baseline (n = 38) had significantly greater improvement in PT score with iron and riboflavin supplementation than without (P = 0.05). Iron and riboflavin supplements significantly reduced the prevalences of riboflavin deficiency (from 60% to 6%; P < 0.0001), iron deficiency anemia (from 35% to 15%; P < 0.007), and abnormal PT (from 87% to 30%; P < 0.05) from baseline. Mean increases in erythrocyte riboflavin (P < 0.0001) and plasma ferritin (P = 0.01) were greater in the FeR + VA group than in the VA only group. Conclusion:Iron deficiency may limit the efficacy of vitamin A to normalize dark adaptation in pregnant Nepali women. Further studies are needed to assess the effect of simultaneous delivery of iron and vitamin A for the treatment of nightblindness.
Micronutrient deficiencies are prevalent in West Africa, particularly among women of reproductive age (WRA) and young children. Bouillon is a promising food fortification vehicle due to its ...widespread consumption. This study aims to evaluate the impact of multiple micronutrient-fortified bouillon cubes, compared to control bouillon cubes (fortified with iodine only), on micronutrient status and hemoglobin concentrations among lactating and non-lactating WRA and young children in northern Ghana. This randomized, controlled doubly-masked trial will be conducted in the Kumbungu and Tolon districts in the Northern Region of Ghana, where prior data indicate multiple micronutrient deficiencies are common. Participants will be: 1) non-pregnant non-lactating WRA (15-49 y), 2) children 2-5 y, and 3) non-pregnant lactating women 4-18 months postpartum. Eligible participants will be randomly assigned to receive household rations of one of two types of bouillon cubes: 1) a multiple micronutrient-fortified bouillon cube containing vitamin A, folic acid, vitamin B12, iron, zinc, and iodine, or 2) a control cube containing iodine only. Evidence from this study will inform discussions about bouillon fortification in Ghana and West Africa.
The estimated average requirement (EAR) for vitamin A (VA) of adult males is based on the amount of dietary VA required to maintain adequate function and provide a modest liver VA reserve (0.07 ...µmol/g). In the present study, the paired-deuterated retinol dilution technique was used to estimate changes in VA pool size in Bangladeshi men from low-income, urban neighborhoods who had small initial VA pool sizes (0.059 ± 0.032 mmol, or 0.047 ± 0.025 µmol/g liver; n = 16). The men were supplemented for 60 d with 1 of 8 different levels of dietary VA, ranging from 100 to 2300 µg/d (2 men/dietary VA level). VA pool size was estimated before and after the supplementation period. The mean change (plus or minus) in VA pool size in the men was plotted against their corresponding levels of daily VA intake and a regression line was fit to the data. The level of intake at which the regression line crossed the x-axis (where estimates of VA pool size remained unchanged) was used as an estimate of the EAR. A VA intake of 254–400 µg/d was sufficient to maintain a small VA pool size (0.059 ± 0.032 mmol) in the Bangladeshi men, corresponding to a VA intake of 362–571 µg/d for a 70-kg U.S. man, which is lower than their current EAR of 625 µg/d. The data suggest that the paired-deuterated retinol dilution technique could be used for estimating the EAR for VA for population subgroups for which there are currently no direct estimates.
Recommendations for vitamin A intake and liver stores are based on maintaining normal vision. We propose that higher levels may be required to maintain normal innate immune function. To test this ...hypothesis, we conducted an 8-wk residential study among 36 healthy Bangladeshi men with low vitamin A stores. Subjects were randomized to receive vitamin A (240 mg in 4 doses) or placebo during study wk 2 and 3. They received 2 vaccines during wk 5 and vitamin A stores were estimated by isotopic dilution at wk 8. The serum concentration of the chemokine interferon-γ-induced protein 10, a component of T-helper 1 (Th1) response, increased significantly after supplementation and was positively and significantly associated with vitamin A stores. Blood concentrations of natural killer (NK) and NK T-cells, which have anticancer and antiviral activity, were positively associated with stores (P < 0.05), as was monocyte oxidative burst (P < 0.05), a marker of bacterial killing ability. However, serum interleukin (IL)-6 and IL-17, cytokines that regulate the antibacterial Th 17 response, were significantly and negatively associated with stores, as was production of the regulatory cytokine IL-10 by whole-blood cultures stimulated with bacterial lipopolysaccharide. In summary, vitamin A stores were positively associated with several measures of innate immune activity across a broad range of stores, suggesting that vitamin A enhances protection against diverse pathogens even at concentrations above those needed to maintain normal vision. The negative association of stores with serum IL-6 and IL-17 suggests that not all protective responses are similarly enhanced by vitamin A. PUBLICATION ABSTRACT
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