Micronutrients

What are micronutrients?

     
Micronutrients are elements or small molecules essential for life but are only required in very small quantities. Examples include dietary minerals and vitamins. This article discusses the main micronutrients, outlining the biological uses of micronutrients and good food sources. Always aim to get micronutrients into the body by eating a wide variety of foods. Supplements should only be used in cases of high requirements (e.g. excessive sweating) or clinical deficiency.

Other small molecules present in plants (phytonutrients) have purported health benefits e.g. the flavonoids may play a role in cancer prevention. However, research is still in its infancy in this area and phytonutrients will therefore not be discussed in detail here.

Electrolytes

  
Sodium, potassium and chloride ions are essential to the regulation of water balance within the body.

Deficiency

Deficiency of sodium, chloride and water, as seen with gastrointestinal diseases (vomiting, diarrhoea), renal (kidney) failure or other renal losses, excessive sweating or loss via burns or dialysis can lead to characteristic symptoms of dehydration – physical exhaustion, reduced blood pressure, cold extremities.

Treatment of mild cases is best achieved by administration of sodium chloride and other salts orally with water being retained in parallel. If the required sodium levels cannot be tolerated orally, then intravenous administration of saline solution may be necessary.

For bodybuilders, excessive loss of ions in sweat does not usually result in clinical issues. However, replacement of electrolytes by use of one of the many proprietary sports drinks is usually sufficient. Sodium may be manipulated during the final days of preparation for a competition. By depleting levels of sodium, a drier look can be achieved that may give your physique the edge.

Deficiency of potassium is again seen in gastrointestinal and renal disease, uncontrolled diabetes, use of diuretic drugs and chronic metabolic acidosis or alkalosis. Symptoms include lethargy, constipation and muscle weakness along with increased thirst and urinary losses. Treatment is generally via potassium supplements.

Excess

 
Symptoms of excess include oedema from water retention, which causes swelling around the ankles and face, and breathlessness when the oedema occurs around the lungs. Retention of sodium and chloride ions in the body is usually due to a failure of part of the circulatory system, leading to the kidney attempting to conserve salt. A reduced sodium diet along with use of diuretics can rectify the symptoms of excess.

Excessive intakes of sodium chloride are common in the Western world, as salt is a frequent addition to processed foods to add flavour. Therefore, people’s palates have changed to favour saltier tasting foods. The result of diets high in salt, even when these do not elevate levels high enough to impact salt content within the body, is often high blood pressure, which can put strain on the heart and lead to heart attacks and strokes.

Bone minerals

 
Calcium
There is 1kg of calcium in the adult skeleton but this is not a static, inactive store. This calcium is in constant flux between the skeleton, kidney and intestine via the blood. This balance is maintained by many hormones, although external factors such as growth, pregnancy or ageing will also affect calcium balance. Calcium is also required for muscle contraction and healthy teeth. It is primarily found in dairy products but is also present at significant levels in dark green vegetables, oily fish with edible bones (e.g. canned sardines and salmon) and pulses.

Vitamin D
Vitamin D is primarily synthesised in the skin on exposure to UV light, although it can be found in relatively low levels in oily fish, eggs and fortified margarine. It has a hormone like action, controlling the absorption of calcium from the intestine and the flux of calcium between the bones and the circulatory system. Vitamin D also plays a role in the immune system.

Phosphorus
85% of the phosphorus in the body is housed within the skeleton, although it plays a vital role in the formation of DNA, ATP and the phospholipids that make up cell membranes. The skeletal form of phosphorus is calcium phosphate and provides stiffness and structure to the bone.

Magnesium
The skeleton contains up to 60% of total body magnesium. Magnesium is also essential for muscle contraction, formation of DNA and is a catalyst for many reactions such as the release of energy from ATP. Deficiency of magnesium has been linked to muscle spasms, cardiovascular disease, high blood pressure and diabetes. Magnesium can be found in dark green vegetables, nuts, seeds and some whole grains.

Deficiency of any one or more of these micronutrients either due to dietary insufficiency or renal disease can lead to bone wasting diseases such as osteoporosis, where the bone composition remains the same but the volume decreases, rendering the sufferer more prone to fractures. However, the causes of osteoporosis are multifaceted and not due to diet alone.

Iron
Iron has vital functions in the body, as a carrier for oxygen (as part of haemoglobin in blood cells and myoglobin in muscle tissue) from the lungs, as a transporter in the ATP generation pathway and as an integral part of many enzyme controlled pathways.

There are two types of iron in the diet – haem and non haem, each with a different mode of absorption from the intestine. Haem iron is present in meat and meat products, whereas non-haem iron is found in plant based products such as dark green vegetables, dried fruit, etc. Haem iron is relatively easily absorbed whereas non-haem iron is influenced by the iron status of the individual. In addition, its absorption is facilitated by vitamin C and meat products and inhibited by calcium, fibre, soy protein and phytates e.g. in grains, fruit, vegetables, seeds and nuts.

Deficiency of iron, where insufficient amounts are mobilised from iron stores, can lead to anaemia. This may be due to dietary inadequacy, parasitic infection (usually in tropical countries) or, in rare cases, tumours causing loss of blood. Symptoms include reduced endurance in relation to physical activity, as oxidative metabolism (and ultimately ATP generation) is impaired. Memory and learning may be affected, along with compromises to the immune system. Pregnancy is also a common time in which iron deficiency anaemia may occur due to the increased demands on the body. Treatment is usually via supplements followed by education on better food choices.

Zinc
Zinc is an essential mineral, required for normal growth of animals and humans. It is a constituent of certain enzymes and acts to stabilise cell membranes. In this way, it plays a role in DNA synthesis, protein digestion and synthesis, carbohydrate metabolism, oxygen transport and protection against free radical damage. Zinc deficiency is difficult to characterise but seems to cause reduced growth rates and reduced immune capacity. It may also play a role in pregnancy complications.

Good sources of zinc are dark red meats with a low fat content and unrefined (whole) grains. However, its absorption is hindered by phytates in wholegrain cereals and other vegetables. Animal protein enhances zinc absorption.

Chromium
Chromium is thought to enhance insulin sensitivity, potentially by increasing the number of insulin receptors or facilitating their interaction with insulin. It has therefore been marketed as a tool for diabetics to increase insulin sensitivity and also as a weight loss aid. However, studies have produced inconsistent results, questioning the essentiality of chromium and its role in the body has yet to be fully elucidated.


Fat soluble vitamins

  
A diet containing some fat is required for the absorption of these vitamins. They are less likely to be lost on cooking than water soluble vitamins but are more likely to build up to toxic levels as they are not excreted from the body in the urine, like water soluble vitamins.

Vitamin A
Vitamin A has two major forms of biological significance – the animal based retinol, found in liver, dairy products and oily fish; and the plant derived ß-carotene, found in orange and dark green vegetables and palm oil (the latter have a lower potency than animal derived vitamin A). Vitamin A is absorbed in the small intestine and mainly stored in the liver.

The best known role of vitamin A is in vision, particularly night vision, as a vitamin A derivative 11-cis retinal, in the sensory areas of the retina. It also plays a role in colour vision. Other major functions are in cell differentiation (i.e. control of gene expression in different cell types, be they a liver or brain cell) and the immune system’s responses to infection.

Deficiency is characterised by night blindness, particularly in the developing world. Dietary inadequacy also increases the risk of infections, especially in children. Treatment is via immediate oral dose of a vitamin A derivative in oil. Prevention is better than treatment and many countries administer large doses of vitamin A as a precaution.

Vitamin A excess is seen acutely, after large doses around 200 times the RNI. Symptoms include nausea, vomiting, headaches, muscular in coordination, blurred vision and vertigo. Drowsiness, lack of appetite, itching, peeling skin and vomiting may then follow. All these symptoms disappear within a week of an acute dose.

The more common chronic toxicity brought on by recurrent ingestion over weeks or years of over 10 times the recommended amount may result in headaches, cracking skin around the lips, dry itchy skin, liver toxicity and bone pain. Most patients fully recover from toxicity, following reduction of vitamin A intake. These symptoms are particularly seen with the acne drug Roaccutane, which also brings about transient increases in serum triglycerides and cholesterol. Excessive intakes of vitamin A also cause severe birth defects, so use of Roaccutane and excessive intakes of dietary vitamin A are contraindicated in pregnancy.

Vitamin D
Vitamin D and its role in bone health has been discussed above. Deficiency is seen in higher latitudes that receive less UV light and also in the elderly and in some Asian populations. The result of deficiency in children is rickets, where the growth and mineralization of the bone is poor, leading to skeletal deformity. In adults, the related condition osteomalacia may ensue, characterised by bone pain, which is easily treated with

 

 

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