Micronutrients is the name given to vitamins, minerals and trace elements required in the diet in very small amounts, unlike macronutrients, such as carbohydrates, protein and fat. Micronutrients are essential for the diet and are needed for the maintenance of health. The micronutrients needed in the human diet are listed below
||Thiamin (vitamin B1)
||Riboflavin (vitamin B2)
Below is a short non-exhaustive list of the function of some of the vitamins and minerals listed in Table 1 above.
Vitamin A is needed for the normal function of the visual system, and maintenance of cell function for growth, epithelial integrity, red blood cell production, immunity and reproduction.
Vitamin C is the major water-soluble antioxidant and acts as the first defence against free radicals in whole blood and plasma.
Vitamin C and vitamin E inhibit oxidation synergistically and act against oxidative stress as potent radical scavenging antioxidants.1,2
Vitamin D is involved in bone health by maintaining calcium and phosphorus homeostasis and promoting bone mineralisation.4 Vitamin D is also implicated in a variety of non-skeletal activities including muscle function, immunity, inflammation and prevention of various diseases, such as certain cancers, autoimmune diseases, cardiovascular diseases and diabetes.5-7Vitamin D deficiency is largely induced by factors such as high latitude (above 35°), seasonality (winter time) and an indoors lifestyle.
Zinc is an essential trace element that is a catalytic component of over 300 enzymes, and also has a role in the structural integrity of proteins and membranes.8 Zinc is required for DNA synthesis, immunity, and sensory functions.
Zinc (Zn) and selenium (Se) are trace minerals with antioxidant properties. They are co-factors of many enzymatic systems, such as the selenium-dependent glutathione peroxidase and the copper (Cu)-Zn superoxide dismutase pathways essential in antioxidative defence.9,10
Calcium is one of the main mineral components of bone tissue and is therefore essential for adequate bone formation. Calcium participates in bone mineralisation, including formation and maintenance of the structure and rigidity of the skeleton.11
During acute and chronic illness, metabolic changes can occur which are caused by pro-inflammatory cytokines that canead to fever, loss of appetite, weight loss, and alterations in fat and trace element metabolism.12 An adequate supply of micronutrients is needed to prevent unwanted clinical conditions due to deficiency or excess. Below is a non-exhaustive list of examples.
Vitamin A deficiency: generates ocular lesions that can lead to blindness.13
Vitamin D deficiency: Vitamin D deficiency is largely induced by factors such as high latitude (above 35°), seasonality (winter time) and an indoor lifestyle.
Iron deficiency: leads to anaemia.14
Iodine deficiency: gives rise to goitre and cretinism which is responsible for developmental delays and other health problems. Iodine deficiency is mainly observed in inland areas where lower quantities of marine foods are available.15
Role of micronutrients during illness
Infection and trauma cause inflammatory stress in patients which may result in tissue damage, enhanced inflammatory mediator production and suppressed lymphocyte function.
In critically ill patients, it has been shown that plasma micronutrient concentrations are low, as a result of increased losses, increased metabolic rate, low intakes and redistribution from plasma to tissue.16
The antioxidant vitamins are important not only for limiting tissue damage, but also in preventing increased cytokine production.17 Supplementation with antioxidants in the acutely ill and chronically ill patient should help improve the antioxidant defence and limit the extent of the inflammatory response.
Micronutrient in Enteral Nutrition
Antioxidant vitamins and trace minerals may improve patient outcome, especially in burns, trauma, and critical illness requiring mechanical ventilation.18,19
Vitamin C and E supplementation of enteral feeds has recently been shown to reduce oxidative stress, thereby reducing the incidence of organ failure and shortening the length of hospital stay.21
Supplementation with zinc, selenium and copper has been shown to improve zinc and selenium status, improve leukocyte count and shorten hospital stay.22 Supplementation of enteral feeds is justified due to the important roles they play in the defence against oxidative stress, and during catabolic stress.