Vitamin A.

20-40 million children in the world have mild vitamin A deficiency and another 3 million have severe vitamin A deficiency leading to high rates of xerophthalmia and blindness. Vitamin A influences growth, survival, and resistance to infection. Vitamin A deficiency reduces the T-cells' ability to fight infection and decreases mucous production resulting in more bacteria being able to attach themselves to respiratory mucosa. Thus it increases the body's susceptibility to respiratory infection. For example, health workers in rural Indonesia who followed children for 18 months and learned that those with mild vitamin A deficiency are twice the risk of respiratory infection than those who do not have such a deficiency. This risk is higher regardless of the children's overall nutritional status. A study in urban India shows the same results. A study in Ethiopia finds children with xerophthalmia not only at increased risk of respiratory infection but also of diarrhea. Other studies demonstrate that respiratory disease, diarrhea, and measles precipitate vitamin A deficiency. For example, corneal ulceration follows an episode of measles in 79% of all corneal ulceration cases in Tanzania. In Indonesia, children with measles are 11 times more likely to have xerophthalmia. Children with mild vitamin A deficiency in Indonesia face death 4 time more often than those with no such deficiency. Vitamin A supplementation decreases mortality 72% in 60-71 month old children and 15% in 12-23 month old children, yet increases it 23% in 36-47 month old children. In Ethiopia, an infection is more predictive of severe, symptomatic vitamin A deficiency than is preexisting malnutrition. Still vitamin A deficiency increases the likelihood of respiratory infection and diarrhea. Thus vitamin A deficient children enter a downward spiral. The longterm solution to vitamin A deficiency is community development and increased consumption of dark green edible plants and red and orange fruits.     

维生素A与多发性硬化

维生素A除了参与维持视力、促进骨骼发育、调节新陈代谢等外,还有广泛的免疫调节作用,为了探讨维生素A与多发性硬化的关系,现就维生素A、多发性硬化与免疫反应间的关系及目前临床相关研究进行简要综述。     

A Method for the Fluorimetric Determination of Vitamin A

¹¹¹In-labelled platelets were used for analysing platelet dynamics in 43 patients with idiopathic thrombocytopenic purpura (ITP). The detected time-activity curves, recorded with a gamma camera, were analysed by three methods: two-and three-compartment models, and an open model in which only the splenic curve was analysed. In the two-compartment model the mean rate constant from blood to spleen was 0.328±0.028 min^-1 (mean±SEM) and from spleen to blood 0.061±0.007 min^-1, whereas in the three-compartment model the corresponding values were 0.236±0.020 and 0.044±0.007 min^-1, respectively. The mean rate constant from blood to liver was 0.466+0.149 min¹ and from liver to blood 0.341±0.106 min^-1 as derived from the three-compartment model. The rate constant from spleen to blood, as determined from the three-compartment model, was significantly higher in patients with a strongly positive result for platelet-associated auto-antibodies (platelet suspension immunofluorescence test (PSIFT)) than in patients with a negative PSIFT. The mean hepatic net rate in patients with a high level of antibodies is into the liver, while in patients with little or no antibodies the net rate is into the blood pool. The mean half-life for the fast component of the inverted splenic curve was 2.5±0.2 min and for the slow component 16±2 min. In patients with a strongly positive PSIFT the half-life for the slow component was significantly longer than in patients with a negative PSIFT. We, therefore, conclude that equilibrium in the exchange of platelets between the spleen and blood is reached more rapidly in patients with a strongly positive PSIFT than in patients with a negative PSIFT.     

Vitamin A and cancer of epithelial origin.

Animal studies have shown. a) an association between vitamin A and cancers of epithelial origin, and b) that vitamin A and its analogues delay tumour appearance, retard tumour growth and regress tumours induced by carcinogenic polycyclic aromatic hydrocarbons. Human epidemiological and biochemical studies suggest that cancers of epithelial origin may be associated with vitamin A deficiency. Vitamin A and its analogues may have a prophylactic and a therapeutic role in cancers of epithelial origin.     

Vitamin A transport in plasma of diabetic patients

The effects of diabetes on the vitamin A metabolism were studied. The concentrations of plasma retinol and retinyl ester were measured in diabetic patients using high-performance liquid chromatography (HPLC). In diabetic patients, the mean level of retinyl ester was significantly elevated compared to that of normal subjects (diabetes, 68.3 +/- 42.5 IU/100 ml of plasma; study I, 87.6 +/- 64.3 IU/100 ml of plasma; study II vs. normal, 29.8 +/- 10.3 IU/100 ml of plasma). The ultracentrifugal and column chromatographic studies were carried out to examine the distribution of retinyl ester in patient's plasma. Ultracentrifugation study showed that the mean of 72.6% of retinyl ester was recovered in the lipoproteins of density higher than 1.006 and the remainder was recovered in the chylomicron (d less than 1.006). Gel filtration profiles for the separation of plasma vitamin A demonstrated that retinyl ester presented in the HDL, LDL and larger molecular size lipoprotein (suspected to be VLDL) as well as in the chylomicron.     

Vitamin D for Health: A Global Perspective

It is now generally accepted that vitamin D deficiency is a worldwide health problem that affects not only musculoskeletal health but also a wide range of acute and chronic diseases. However, there remains cynicism about the lack of randomized controlled trials to support the association studies regarding the nonskeletal health benefits of vitamin D. This review was obtained by searching English-language studies published up to April 1, 2013, in PubMed, MEDLINE, and the Cochrane Central Register of Controlled Trials (search terms: vitamin D and supplementation) and focuses on recent challenges regarding the definition of vitamin D deficiency and how to achieve optimal serum 25-hydroxyvitamin D concentrations from dietary sources, supplements, and sun exposure. The effect of vitamin D on fetal programming epigenetics and gene regulation could potentially explain why vitamin D has been reported to have such wide-ranging health benefits throughout life. There is potentially a great upside to increasing the vitamin D status of children and adults worldwide for improving musculoskeletal health and reducing the risk of chronic illnesses, including some cancers, autoimmune diseases, infectious diseases, type 2 diabetes mellitus, neurocognitive disorders, and mortality.     

Metabolism of the Vitamin A Transporting Protein Complex

Abstract. Biological turnover studies of the human vitamin A transporting protein complex and its individual components, prealbumin and retinol binding protein (RBP) have been performed in normal persons and in patients with severely impaired kidney function. The metabolic behaviour of prealbumin was very similar in the two groups of subjects studied, and it was concluded that prealbumin eatabolism can be dependent to only a minor extent on normally functioning kidney glomeruli.–RBP is present in several molecular forms in plasma. In normal conditions virtually all PRB is bound to prealbumin, but small amounts of RBP also occur in free form. The concentration of the free RBP is greatly increased in patients with grossly impaired glomerular filtration. The biological half-life for free RBP was short in normal persons (about 4 hours) whereas in the patients this parameter was increased 10 to 15 fold. These findings suggest that most if not all free RBP in plasma is catabolized by the kidney. RBP complexed with prealbumin has a considerably longer half-life than its free counterpart in normal persons but the absolute synthetic rate of the two components of RBP is similar. Thus it is proposed that most RBP is catabolized from the pool of the uneomplexed species.–From the data it can be calculated that as much as one third of the plasma vitamin A may be deposited in the kidney tubuli on degradation of RBP, since the mechanism for the renal eatabolism of this small protein seems to involve glomerular filtration followed by tubular reabsorption.