Vitamin A, inadequacy

Duitsman PK, Cook LR, Tanumihardjo SA, Olson JA (1995) Vitamin A inadequacy in socioeconomically disadvantaged pregnant Iowan women as assessed by the modified relative dose response (MRDR) test. Nutr Res 15 1263-1276... 

Tissue reserves of retinoids in the healthy adult are sufficiently large to require long-term dietary deprivation to induce deficiency. Vitamin A deficiency occurs more commonly in chronic diseases affecting fat absorption, such as biliary tract or pancreatic insufficiency, sprue, Crohn s disease involving the terminal ileum, and portal cirrhosis deficiency may also occur following partial gastrectomy or during extreme, chronic dietary inadequacy. 

Adipocytes have vitamin D receptors, and there is evidence that vitamin D may act as a suppressor of adipocyte development (Kawada et al., 1996). It has been suggested that vitamin D inadequacy may be a factor in the development of the metabolic syndrome ( syndrome X, the combination of insulin resistance, hyperlipidemia, and atherosclerosis associated with abdominal obesity). Sunlight exposure, and hence vitamin D status, may be a factor in the difference in incidence of atherosclerosis and myocardial infarction between northern and southern European countries in addition to effects on adipocyte development, calcitriol also enhances insulin secretion through induction of calbindin-D (Section 3.3.7.1), and there is some evidence vitamin D supplements can improve glucose tolerance (Boucher, 1998). 

In Malaysia reports indicate that clinical vitamin A deficiency is uncommon, apart from severe PEM admissions to pediatric wards (Y. H. Chong, 1981, personal communication). There is evidence of subclinical hypovitaminosis A and dietary inadequacy, especially among Malay children from traditional families (Chen, 1972). One study reported one-third of the preschool children and one-fifth of the school children on a rubber plantation had serum vitamin A levels >20 xg/dl (Ng and Chong, 1977). Mean vitamin levels of breast milk are low (13 juig/dl mature milk) among rural women, but they are adequate among urban mothers (63 xg/dl) (Y. H. Chong, 1981, personal communication). 

A number of studies have shown that between 10 and 20% of the apparently healthy population have low plasma concentrations of pyridoxal phosphate or abnormal erythrocyte transaminase activation coefficient, suggesting vitamin Bg inadequacy or deficiency. In most studies, only one of these indices of vitamin Bg nutritional status has been assessed. Where both have been assessed, while each shows some 10% of the population apparently inadequately provided with vitamin Bg, few of the subjects show inadequacy by both criteria. 

Vitamin D is a family of closely related molecules that prevent rickets, a childhood disease characterized by inadequate intestinal absorption and kidney reabsorption of calcium and phosphate. These inadequacies eventually lead to the demineralization of bones. The symptoms of rickets include bowlegs,... 

The absorption of vitamins K2, which are found mainly in cheese, curd cheese, and natto, is much higher and may be almost complete. Thus the nutritional importance of menaquinones is often underestimated. The vitamin K activity is related to the activation of specific proteins involved in blood clotting and bone metabolism. Clinical vitamin deficiency due to dietary inadequacy is rare or nonexistent in healthy adults, thanks to the widespread distribution of the vitamin K in foodstuffs and the microbiological flora of the gut, which synthesizes menaquinones. Only infants up to 6 months are at risk of bleeding due to a vitamin K deficiency. No data on negative effects of an overdose of vitamin K are found [417]. 

Marginal inadequacy, affecting amino acid metabolism and possibly also steroid hormone responsiveness, may be relatively common. A number of vitamin Be dependency syndromes have been reported - inborn errors of metabolism in which the defect is in the coenzyme binding site of the affected enzyme. 

In addition to nutritional inadequacy, vitamin deficiency may result from malabsorption, effects of pharmacological agents, and abnormalities of vitamin metabolism or utilization. Thus, in biliary obstruction or pancreatic disease, the fat-soluble vitamins are poorly absorbed despite adequate dietary intake because of steatorrhea. Absorption, transport, activation, and utilization of vitamins require the participation of enzymes or other proteins whose synthesis is under genetic control. Dysfunction or absence of one of these proteins can produce a disease that is clinically indistinguishable from one caused by dietary deficiency. In vitamin-dependent or vitamin-responsive... 

Inadequacies in the maternal diet during lactation may have severe consequences. The woman s health status may deteriorate as a result of large withdrawals of nutrients from her tissues. A poor maternal diet will also result in a decreased volume of breast milk. Also, there will be a reduction in vitamin levels. As a result, the infant may be shortchanged with regard to calories and essential nutrients. 

Increased vitamins may be needed for therapeutic reasons. Vitamin supplementation may be needed when a person is unable to consume an adequate diet due to illness, allergies, or emotional upsets. Likewise, vitamin supplementation may be prescribed when a serious dietary deficiency has occurred because of ignorance or poor eating habits however, such supplementation should never replace the correction of factors leading to the dietary inadequacy. At such times, vitamin supplementation should be taken on the recommendation of physicians to help control particular conditions diagnosed by them. 

Inadequacy of the enzyme system may play a role the available amount of endogenous thiosulphate is certainly a factor. Patients with Leber s optic atrophy or tobacco amblyopia have already relatively high cya-nide/thiocyanate levels and the use of nitroprusside in such patients is contraindicated, as it is in patients with deranged liver function and with vitamin BI2 deficiency. 

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