Vitamins!

Small concentrations of vitamins can be found in foods. Each vitamin has a particular and unique role to play within the body. Vitamins are essential within the diet as the human body is not able to synethesise most vitamins (except vitamins D and K. Some foods contain precursors or provitamins of specific vitamins – that is, they need to be converted by the body into the active vitamin before they can exhibit the characteristic functions.

Vitamins are divided into two categories:

Fat Soluble and
Water Soluble.

Vitamin D, Vitamin A, Vitamin E and Vitamin K are fat soluble – that is, they are carried on fats in the body, and stored in adipose tissue (fat cells) and the liver. If a person has a condition restricting fat absorption, then it will also reduce absorption of fat soluble vitamins. As these vitamins can be stored in the body, deficiencies can be slow to develop. On the other hand, risk of toxicity from these vitamins is also greater.

The B group vitamins along with Vitamin C, are water soluble. They can be flushed through the body, and are unable to be stored. The potency of the vitamins can be lost when foods with these vitamins are boiled or soaked.

The human body doesn’t gain energy directly from Vitamins. Vitamins assist the mechanisms of the body to produce energy. Most Western diets contain enough vitamins, so supplementation is rarely required. If vitamins are lost through poor food storage and preparation then supplements may be required to replace those deficiencies. Also, if there is a low level or poor absorption of vitamins in food, or higher rate of utilisation of the vitamins, then vitamin intake may not be optimal.

Vitamin A

Vitamin A is a fat soluble vitamin, meaning the body can store it within the fat cells. The functions of Vitamin A are to assist in bone growth, vision and the formation of cells on the surface of the skin and the lining of the gut. There are two dietary forms of Vitamin A:

one form, known as retinol and
second form, B-carotene (pro-Vitamin A).

Retinol is found in animal sources including full cream dairy products, eggs, margarine, butter and liver.

B-carotene is converted into vitamin A within the intestine. You will find B-carotene in deep yellow, orange and green fruit and vegetables. This form also has great antioxidant properties.

Vitamin A has a recommended daily intake (RDI) of 750ug retinol equivalents/day for men and women. Each 1ug of B-carotene is equivalent to the biological activity of 1/6ug retinol, however the absorption of B-carotene may further lower this amount. (The RDI for vitamin A is measured in retinol equivalents because this then takes into account sources from both forms of vitamin A.)

Vitamin A deficiencies can lead to blindness, stunted growth, reduced appetite, and decreased immunity. Most Western diets contain adequate levels of Vitamin A and therefore deficiencies are rare. Excessive quantities of the retinol form of vitamin A can be stored in the liver and have toxic side effects. These side effects include nausea, vomiting, lethargy, dry skin and loss of appetite. An over-consumption of B-carotene can cause orange pigmentation of the skin. If overdose of the retinol form are consumed during pregnancy, congenital abnormalities can result in the foetus.

Food Sources of Vitamin A

Food Source	Retinol (ug/100g)	Carotene (ug/100g)	Notes	RDI
High
Cod Liver Oil	28,400	1050	Maximum of 30-40% loss in cooking. Both retinol and carotene are sensitive to light and oxygen	Adults over 11 yrs – 750ug
Palm Oil	0	7000
Fried lambs Liver	20,600	10
Medium
Carrots	0	2000
Spinach	0	1000
Sweet Potato	0	670
Egg Yolk	660	100
Low
Bread	0	0
Potato	0	Trace
Chicken	Trace	Trace

Note: mg=1/1000 of a gram
ug=1/1000 of a mg

Vitamin D

There are several forms of Vitamin D – vitamin D3 (the main form) will be discussed here, and will be referred to as vitamin D. Vitamin D is produced in the liver and kidneys following the skin’s absorption of sunlight.

Its major function is to increase the absorption of calcium and phosphate from the intestine, thus enhancing bone formation. It also reduces excessive cell division and can regulate the immune system. Small amounts of vitamin D are present in eggs, butter, and fatty fish.

It has long been thought that people who receive adequate sunlight are not at risk of Vitamin D deficiency. However, it has recently been found that a significant proportion of the population may be deficient in Vitamin D. Particular at-risk groups include infants living in cold environments with minimal exposure of the skin to sunlight, institutionalised people (e.g. in nursing homes), or those required to cover up with clothing for religious or race-related reasons, hence they may need supplementation.

A deficiency of vitamin D may also occur when there is a problem of the liver or kidney, so vitamin D cannot be made.

Deficiency can result in rickets in children, and osteomalacia, or bone thinning in adults.

Food Source	Vitamin D (ug/100g)	Notes	RDI
High
Cod Liver Oil	210	Maximum of 40% loss in cooking. Stable to heat, aging and storage.	Infants and young children: 400 I.U (International Units). No normal recommended intake is given for adults as they seem to gain adequate from normal exposure to sunlight.
Medium
Fatty Fish	5 – 25
Margarine	8
Low
Egg yolk	5
Butter	1
Cheese	0.2
Milk	0.01

Source: Walqvist, Food and Nutrition.

Vitamin E

Like many of the other vitamins, Vitamin E, has several different forms known as tocopherols. The a-tocopherol form is the most important form.

Minor benefits of vitamin E are in nerves and muscle function. The main benefit of vitamin E is its antioxidant properties. It can help to prevent oxidative damage to the arteries near the heart (a major cause of atherosclerosis). Polyunsaturated fats can be converted by oxygen into free radicals, so the greater the intake of these fats, the more vitamin E is required.

Foods containing vitamin E include wheat germ, peanuts and olives, as well as polyunsaturated margarine. Grains, seeds, nuts, fish and dairy products also have good amounts of vitamin E. The RDI for adults is 7 – 10mg/day.

Symptoms of deficiency can include nerve cell and muscle fibre problems, as well as excess red blood cell breakdown. However, many of the polyunsaturated fat sources contain Vitamin E, so deficiencies are rare. Megadoses of vitamin E can lead to weakness, fatigue and dermatitis.

Food Source	Vitamin E (mg/100g)	Notes	RDI
High
Wheat germ oil	140	Maximum 55% loss in cooking, sensitive to heat and oxygen and decomposes in sunlight	8 yrs and over – 7-10mg/day
Polyunsaturated vegetable oil	20-80
Medium
Peanut oil	15-20
Olive oil	5
Nuts, seeds, whole grains	1-20
Low
Milk	0.02

Source: Walqvist, Food and Nutrition

Vitamin K

Vitamin K foods have great benefits. The most important role of vitamin K is blood clotting. This helps to prevent excessive bleeding.

Approximately half the body’s requirement for vitamin K is synthesised by bacteria in the intestine, however substances which destroy bacteria (e.g. antibiotics) can increase vitamin K requirements. The remainder can be obtained from sources including green leafy vegetables, carrots, soy beans and wheat bran.

There is no RDI for vitamin K, considering the amount synthesised in the intestine varies. Deficiencies are rare, and will result in haemorrhage. Newborns are usually given a dose of vitamin K due to low body stores and lack of bacteria in the intestine. They then receive vitamin K via breast milk, allowing time to increase their stores and synthesise bacteria.

Vitamin K is a fat soluble vitamin.

Food Source	Vitamin K (ug/100g	Notes	RDI
High
Spinach	240	Maximum of 5% cooking loss. Sensitive to light, oxygen and both acid and alkali conditions	U.S.A. 70-140ug/day for men and women
Soy beans	190
Cabbage	100
Medium
Bran (wheat)	80
Green beans	20
Pork liver	20
Low
Oranges and apples	Less than 5

Source: Walqvist, Food and Nutrition

Comments

comments