Vitamins are chemical substances that are vital for good health. They are important for many daily bodily functions, such as growth and cell reproduction. Because the body cannot store some of the 13 vitamins it needs, a regular intake is important.
Most people easily meet their daily vitamin needs by eating a varied diet based on foods from the 5 food groups, including breads and cereals, fruit, vegetables, meat, fish, eggs or plant foods such as legumes, nuts and seeds, milk, yoghurt and cheese.
While an adequate intake of vitamins is essential for health, taking more than needed does not usually confer any extra health benefit and can, sometimes, be dangerous. The Nutrient Reference Values for Australia and New Zealand give recommended Dietary Intakes for vitamins.
Most vitamins are provided by food and are divided into 2 groups.
1. Fat soluble vitamins
- Vitamin A: is available as 'ready-made' retinol or in the form of beta-carotene. Retinol occurs in liver, oily fish (such as sardines, gemfish and herring) and dairy fat. Carotenes, especially beta-carotene in red, orange and yellow coloured fruit and vegetables and leafy green vegetables, are converted to retinol.
- Vitamin D: present in mushrooms that have been subjected to light and in small quantities in butter and margarine and eggs. Our bodies manufacture vitamin D starting with the action of sun on our skin.
- Vitamin E: found in 8 different forms in foods, especially sunflower, safflower and olive oils, almonds, hazelnuts, peanuts and seeds (pepitas, sunflower and sesame), tahini and salmon.
- Vitamin K: from vegetables, especially spinach, broccoli, red, green or Asian cabbage, lettuce, parsley and coriander.
Fat soluble vitamins, as the name implies, can be stored in fats and hence we tend to maintain adequate levels in the body for longer - up to 2 years - after our intake drops.
People who have a low fat intake or whose fat metabolism is affected by drugs or disease can become deficient in fat-soluble vitamins.
Conversely, an excess of fat soluble vitamins over time can lead them to building up in the body, potentially leading to toxic levels.
Fat soluble vitamins are not affected by cooking.
2. Water soluble vitamins
- Vitamin B group: B1 (thiamin), B2 (riboflavin), B3 (niacin), B5 (pantothenic acid), B6 (pyridoxine), B7 (biotin) - are widely distributed in foods including meat, poultry, seafood, wholegrains, bread, wholegrain and fortified breakfast cereals, pulses (dried beans and lentils), nuts, dairy products, eggs, vegetables, fruit and yeast extract.
- Vitamin B12 is found only in animal products, meat, poultry, seafood, eggs, milk, yoghurt and cheese. Some plants contain a similar compound, but it cannot substitute for vitamin B12.
- Folate (variously called B9 or B10): is found in green vegetables (its name derives from foliage), cauliflower, beetroot, sweetcorn, liver, yeast extract, pulses, wholegrain cereals, nuts, oranges and berries. A synthetic form called folic acid is added to some breakfast cereals and breads.
- Vitamin C: found in fresh and frozen fruit and vegetables, particularly citrus fruits.
Water soluble vitamins that are surplus to requirements are simply excreted in the urine, so generally don't build up to toxic levels in the body.
The effects of a low intake of water-soluble vitamins are generally seen sooner, although it may take weeks or months of poor diet for symptoms to appear. Historically, the clearest example of this was scurvy, the result of vitamin C deficiency that occurred when sailors had been at sea for some months without fresh fruit or vegetables.
Some water soluble vitamins are lost from vegetables during cooking. Boiling or overcooking leads to large losses. The cooking methods that keep the most water-soluble vitamins are microwaving or steaming.