Vitamins

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Vitamin A

Vitamin A is provided in two forms as retinol – animal-derived, pre-formed vitamin A, and as beta-carotene – vegetable-derived vitamin A which needs to be converted into retinol.  By standard convention in the UK 6 parts of beta-carotene are needed to produce one part of retinol.  The food content of retinol is then expressed as Retinol Equivalents, REs, made up of the total of retinol plus one sixth of the dietary content of beta-carotene.
However in the United States the calculation of retinol from beta-carotene is one sixth that from supplements but only one twelfth that from food sources and their terminology is Retinol Activity Equivalents, RAEs, rather than REs.  In the US the retinol content of liver and cheese is considerably lower than that in the UK and the data is included for comparison.  The contents of retinol for full-fat milk and cream in the UK and US are however very similar.

In the UK as well as many countries around the world margarine is, by law, fortified with retinol to the level found in butter during the summer months.  The average UK diet provides approximately two thirds of vitamin A as retinol and one third as beta-carotene. Additionally there appears to be considerable individual variation in the efficiency of conversion of beta-carotene to retinol, with males being more efficient than women.

Adult Requirements and Intakes

Average Percentage of Intake Provided by Nutritional Supplements

Pre-formed Retinol

Beta-Carotene

Content of Individual Foods - Retinol

* Fortified food
^ United States Department of Agriculture National Nutrient Database, Standard Release 20.
www.ars.usda.gov/Aboutus/docs.htm?docid=6300

RAE, Retinol Activity Equivalents, the US measure of retinol activity

Content of Individual Foods – Beta-Carotene

Vitamin D

The two main forms of vitamin D are ergocalciferol (vitamin D2), which is derived from plant sources and cholecalciferol (vitamin D3), which is derived from animal sources by the action of sunlight on the skin.  Dietary vitamin D, which is mainly of animal origin, only provides 10% of our requirement with the remainder coming from sunlight exposure.  As the rate of production declines in the elderly and is less in those of non-European origins with darkened skin and in anyone with poor sun exposure the dietary intakes become particularly important.  It is, however, difficult for the whole requirement to be fulfilled adequately by diet alone.

Adult Requirements and Intakes

*None – if adequate sunlight exposure

10 ug/day for those:

• aged 65 years or more
• inadequate sun exposure
• pregnant or lactating women

Average Percentage of (Dietary) Intake Provided by Nutritional Supplements

Content of Individual Foods

*Fortified food
**The skin of rainbow trout contains 24ug vitamin D per 100g

Vitamin E

This vitamin is present in foods as two series of compounds, four tocopherols and four tocotrienols, each having a different level of vitamin E activity.  The main food sources are nuts and seeds and oils derived from them.  Though the content of vitamin E is quite stable at room temperature, when heated in air the vitamin E soon oxidises and its chemical activity is lost.
Vitamin E activity is expressed as α-tocopherol equivalents, which is the sum of α-tocopherol, 40% of the β-tocopherol, 10% of the γ-tocopherol, 1% of the δ-tocopherol, 30% of α-tocotrienol, 5% of the β-tocotrienol, 1% of the γ-tocotrienol and 1% of δ-tocotrienol.

Adult Requirements and Intakes

Average Percentage of Intake Provided by Nutritional Supplements

Vitamin K

Vitamin K is derived from two sources, phylloquinone, which is derived from plant sources and menaquinones, which are synthesised by bacteria resident in the bowel.  Adults can become deficient as a result of a poor diet or Persistent use of antibiotics.

Adult Requirements and Intakes

Requirements are considered to normally be in the range of 0.5 and 1.0 ug/kg body weight/day.

Average Percentage of Intake Provided by Nutritional Supplements
Not assessed

Content of Individual Foods

Vitamin B1 (Thiamin)

The requirement for vitamin B1, thiamin, is dependent upon total energy intake due to its importance in the metabolism of carbohydrates, fats and alcohol.  Thiamin is very water soluble and is easily lost in the preparing and cooking of food.  Processed foods contain much less than their initial ingredients and some such as white flour, white bread, and some breakfast cereals are fortified with this vitamin as well as other nutrients. 

Adult Requirements and Intakes

Based upon an energy EAR of 1900 kcl/day for women and 2,550 kcl/day for men.

Average Percentage of Intake Provided by Nutritional Supplements

Content of Individual Foods

* Fortified food

Vitamin B2 (Riboflavin)

Riboflavin together with thiamin and vitamin B3 plays an important role in energy production.  It is less water-soluble than thiamin and thus less is lost in food preparation and cooking.  However, it is easily destroyed by bright sunlight.  Riboflavin has a bright yellow/green colour which is evident in the urine after high-dose supplements are taken.

Adult Requirements and Intakes

Average Percentage of Intake Provided by Nutritional Supplements

Content of Individual Foods

Vitamin B3 (Niacin)

Vitamin B3 exists in two forms as niacin (nicotinic acid) and as nicotinamide.  They can be obtained preformed from the diet but approximately half of our requirement is fulfilled from the conversion from the amino acid tryptophan by a vitamin B6 dependent enzyme.  The total intake is expressed as niacin equivalents, defined as total niacin intake plus one sixtieth of the tryptophan content of the diet.
The requirement for vitamin B3 is dependent upon energy intake.

Adult Requirements and Intakes

 Based upon an energy EAR of 1900 kcl/day for women and 2,550 kcl/day for men

Average Percentage of Intake Provided by Nutritional Supplements

Content of Individual Foods

*Fortified food

Vitamin B5 (Pantothenic acid)

Pantothenic acid is widely distributed in foods and thus intakes are almost always satisfactory.  It plays a central role in the release of energy from all sources.  Because deficiency is rare and difficult to induce it has been difficult to precisely identify requirements. 

Adult Requirements and Intakes

Average Percentage of Intake Provided by Nutritional Supplements

Content of Individual Foods

Vitamin B6

The term vitamin B6 includes pyridoxal, pyridoxamine and pyridoxine and their 5’-phosphate forms which are interconvertible.  Requirement is related to protein intake due to its relation to amino acid metabolism.  It is heat sensitive and deficiency has resulted in infants from the severe over-heating of formula milk.

Adult Requirements and Intakes

Based upon a protein intake of 55 g/day for men and 45 g/day for women.

Average Percentage of Intake Provided by Nutritional Supplements

Content of Individual Foods

Folate

Folate is the form of this vitamin found in foods, especially green leafy vegetables (foliage), and folic acid is the simpler chemical form that is used as a supplement or added to foods.  Folate is needed for rapidly dividing cells hence deficiency can affect the health of a pregnancy, the bone marrow and anaemia and the lining of the gastrointestinal tract.  At present consideration is being given to fortifying flour and perhaps other foods in the UK as has happened in the United States, in order to reduce the risk of pregnancies being affected by neural tube defects (spina bifida). 

Adult Requirements and Intakes

Average Percentage of Intake Provided by Nutritional Supplements

Content of Individual Foods

* Fortified food

Vitamin B12

This vitamin is only found in animal-based foods and the body normally has a store in the liver which can last up to four years.  Unlike the other B vitamins it is relatively stable during cooking.  Deficiency can result from consuming an inadequate vegan or poor quality vegetarian diet but is also not uncommon in the elderly due to absorption difficulties.  For this reason in the US those aged over 50 years are advised to eat foods fortified with vitamin B12 or to take a supplement.   

Adult Requirements and Intakes

Average Percentage of Intake Provided by Nutritional Supplements

Content of Individual Foods

* Fortified food

Biotin

This B vitamin is required for fat metabolism and deficiency is rare but can occur as a result of consuming raw eggs.  The whites contain a protein, avidin, which binds with biotin making it unavailable for absorption.  Paradoxically a good source is egg yolk, as is meat and offal. 

Adult Requirements and Intakes

Average Percentage of Intake Provided by Nutritional Supplements

Content of Individual Foods

Vitamin C (Ascorbic acid)

Vitamin C has played a central role in the understanding of essential micronutrients as deficiency causes scurvy, which has been known since historic times and developed in seafarers due to their reduced intake of fruit and vegetables.  Vitamin C is added to foods as a natural preservative as it helps to reduce food spoilage from oxidation due to exposure to the air.  The low content of vitamin C in some apples results in them browning quickly when cut.

Adult Requirements and Intakes

Average Percentage of Intake Provided by Nutritional Supplements

Content of Individual Foods

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