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Vitamin deficiencies are often considered to be a thing of the past in the industrialised world, and their primary clinical symptoms and signs are poorly known. While they are certainly rarer in the West than in the developing countries, they are nonetheless more common than thought .
Vitamin deficiencies are common in poor countries as a result of malnutrition, an imbalanced diet or insufficient intake of vitamin-rich foods. These selective deficiencies cause a recognisable set of clinical symptoms and signs (table I). Severe global malnutrition causes such conditions as marasmus or kwashiorkor, in which multiple vitamin deficiencies are present and combined with trace element deficiencies [9, 26].
Vitamin deficiencies in the affluent West tend to be selective in nature. They arise as a result of a discrepancy between supply and demand for a given vitamin and are more often linked to the body’s inability to use the vitamin correctly than inadequate dietary intake.
1.1 - STRUCTURE AND SOURCE OF VITAMINS
In themselves, vitamins have no energy value. They are active at low doses but are essential for the organism since the human body is unable to synthesis them. They are implicated in numerous vital metabolic processes. There are thirteen groups of vitamins divided into the hydrosoluble vitamins (vitamin C and the group B vitamins) and liposoluble vitamins (vitamins A, D, E and K). The main roles played by vitamins and their principal sources in the diet are shown in Table II .
1.2 - VITAMIN REQUIREMENTS AND RECOMMENDED DAILY INTAKES
A reminder of the recommended daily intakes by gender and age are provided in Table III and Table IV  ; the amounts shown cover the needs of most people. Recent food surveys highlighted the fact that intake of some vitamins in large proportions of the population studied did not meet the internationally recommended daily amounts .
1.3 - THE CONCEPT OF INADEQUACY
Progress made in the field of nutritional biology over the past years has shown that the clinical signs of deficiency are but a faint echo of the actual biological roles played by vitamins. Several epidemiological studies and experimental studies in man and animals have evidenced the impact of certain vitamin deficiencies on health . For instance, recent studies have demonstrated that a low vitamin C intake (without causing scurvy) could be a risk factor for ischaemic heart disease and cancer. Similarly, when ingested in quantities less than the recommended daily intake in France (without causing osteomalacia), vitamin D is believed to enhance the risk of certain cancers, arterial hypertension – particularly during pregnancy -, infectious diseases such as tuberculosis and certain auto-immune disorders . Thus, we have moved away from the classic concept of deficiency (which is still commonly encountered in the developing countries as a result of chronic food shortages but is relatively rare in the industrialised West and tends to be related to chronic disease or deliberately restricted food intake) towards the new concept of inadequacy (of the type seen in the industrialised countries), whose consequences are a result of the multiple roles played by vitamins in many major metabolic processes.
1.4 - GROUPS AT RISK OF DEVELOPING VITAMIN DEFICIENCIES
Some population groups appear to be at high risk of developing a vitamin deficiency in certain circumstances. Examples include gastrointestinal disease or surgery causing vitamin malabsorption or depletion, liver disease, chronic renal disease or AIDS and patients with congenital or hereditary metabolic disorders. Prolonged parenteral nutrition is a major cause of vitamin deficiency. Deficiencies may also arise sporadically as a result of a combination of acquired factors such as pregnancy and breast-feeding, prematurity, poverty, obesity, recent immigration, adolescence, ageing or medicinal product intake. Alcoholism causes a variety of vitamin deficiencies as a result of the loss of appetite, liver disorders and poor diet with which it is associated . The vitamin deficiencies caused by an imbalanced diet – whether as a result of personal conviction (vegetarian, vegan or macrobiotic), dietary negligence or error (strict elimination diet in allergic subjects or when lactose intolerance is suspected) , or caused by anorexia, drug dependency or psychosis – are also non negligible. There are currently a number of nutritionally-unsound "fad" weight-loss or well-being diets .
1.5 - POSITIVE DIAGNOSIS OF A VITAMIN DEFICIENCY
Vitamin deficiencies are difficult to diagnose. A deficiency is not always considered as a possible diagnosis and the clinical signs – with which both patients and healthcare providers may be unfamiliar - are difficult to analyse. Their impact on the skin varies in type and intensity depending on which vitamin is lacking. Some cutaneous signs are second-tier as they are not specific and are seen with other deficiencies. Conversely, with pellagra or scurvy, the cutaneous signs are primordial (see Table I)
If a vitamin deficiency is suspected, a brief enquiry into dietary habits (regular consumption of foods from the four main groups, i.e. milk products and eggs, meat and fish, cereals and fresh fruit and vegetables) is extremely useful.
It is often difficult to detect a vitamin deficiency via laboratory tests and the results are unreliable, which further complicates their diagnosis. Moreover, most vitamin assays (thiamine, riboflavin, biotin, phylloquinone or ascorbic acid) are not covered by the national health insurance scheme in France. Blood or urine concentrations are often a simple reflection of recent consumption of the vitamin tested for and do not give a true picture of the subject’s vitamin levels. A true vitamin deficiency arises when the vitamin stock is depleted and, for some vitamins, serum concentrations are not an accurate reflection of the amount remaining in the body. Ideally, a tissue assay should be done. A vitamin deficiency is only truly proven when the symptoms resolve after presumptive supplementation with the vitamin in question.
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