Prof. James Renner and Prof. Roger Andrianasolo
Nutrition has been implicated in several diseases including infections. Clinical and epidemiological data indicate that undernutrition predisposes to infection. The converse that infection could lead to malnutrition is also true. Protection against infections is enhanced by good nutrition. What then is the link between these?
Nutrition, health and disease
The role of nutrition in disease prevention and health maintenance is no longer in doubt. It plays very significant role in health from conception to old age1. Poor nutrition has been linked to chronic diseases such as metabolic syndromes, bronchial asthma, allergy, neoplastic diseases and coronary heart disease to mention a few.2 Nutrients which consist of macro and micronutrients should be consumed in the right quantity and quality to be useful. There are several reasons why it may not always be possible to consume quality nutrients particularly in the deprived economies and more so in children in those communities. Significantly, poverty and ignorance top the reasons for this; food and nutrition security play leading roles in this with resultant malnutrition.
Most times when the subject of nutritional deprivation is discussed, the emphasis is unfortunately hinged on macronutrients (Carbohydrate, Lipid and Protein). While these are useful it should be borne in mind that micronutrients which are vitamins (water and fat soluble) and trace elements (such as zinc, selenium, iron, iodine) enhance the functions of the macronutrients because of synergistic interactions. For instance the metabolism of carbohydrate is enhanced by thiamine, the absence of which leads to Beriberi. There are many other examples that could be provided but time and space allowed do not permit for further elaboration. To prevent malnutrition therefore attention should be paid to the consumption of both macro and micronutrients
Malnutrition, Infection and immunology
Host defence against infection is dependent on specific immunological status and non-specific factors of resistance. The immunological arm consists of Humoral the B- (Bone marrow derived) cells and Cellular T- cell (Thymus derived) cells arms. The B-cells are responsible for the production of immunoglobulins with identified functions and antibody production. The T-cell on the other hand is responsible for cell-mediated immunity such as delayed hypersensitivity, graft rejection and cytotoxicity. The T and B cells and their products along side with macrophages, complement system are involved in protecting against infection. The mechanism of action of these systems involves enzymes which are proteins. These would involve receptors, trace elements such as zinc, iron and minerals such as magnesium and calcium to mention a few. Also required will be energy from carbohydrate and fat. These have to be provided from nutrients in adequate quantity and quality to ensure that the defence system is optimal otherwise vulnerability to infection is high.
Infection, conversely, no matter how mild, can precipitate malnutrition. Infection leads to poor or loss of appetite, increased metabolic rate. There also is loss of nutrient in stool as in gastroenteritis. Severe viral illness such as measles in children commonly results in malnutrition. It is now possible to attenuate the severity of and possibly prevent these consequences with prophylaxis of vitamin A and Zinc supplementation. This has been found quite useful in acute respiratory infection and acute diarrheal diseases.
From the foregoing, without doubt, either of infection or malnutrition can predispose to the other 3. This is a vicious cycle which can be broken. The link obviously is immunological4,5,6. The problem is predominantly one of the challenges of under- five- children in the developing countries. Enhancing the nutritional status of the children and implementing the immunization programmes will be a great step in tackling the challenges. Other aspects of infection control cannot be ignored.
Water and sanitation, including availability of potable water, proper disposal of refuse and human waste, appropriate housing and food and nutrition security will go a long way to be part of the solution3.
Exclusive breast feeding for the first six months of life and provision of appropriate complementary food while still breast feeding are an indispensible activity that has been shown to help protecting against infection and reducing morbidity and mortality7.
Nutrition depletion leading to malnutrition impairs body resistance to infection. Conversely, infections no matter how mild have significant effect on nutritional status. The mechanism of this vicious cycle has been elucidated to a large extent. The various arms of the defence system against infection require adequate nutrition for optimal function. In nutritional depletion this protection is impaired. The way out is obvious- enhanced nutrition and improved immunological status.
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