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The Complete Guide to Vitamins

In this chapter of “The Complete Guide” we will look at the different vitamins and why we need them. You may be interested in all of them, or you may just have a special interest in some of them. Either way, this article is intended to give you a brief, easy to understand guide as to which vitamins perform which functions in our body.

Vitamin A

When we refer to vitamin A, we generally use the term to include carotenoids, which are the precursors to retinol. These are found in many fruits and vegetables,¹ especially the orange, yellow and red varieties. Pre-formed vitamin A is actually mainly available in animal products such as red meat, liver, eggs and some fish.² Unlike some nutrients which are deteriorated by cooking, carotenoids become more bio-available when food is cut up and/or cooked.¹

This nutrient is incredibly important to our visual health. As retinaldehyde it is essential for maintaining vision as it forms a component of Rhodopsin, the light sensitive part of the retina. A deficiency in vitamin A can lead to photoreceptor degeneration, causing night blindness, which is reversible in the initial stages, but can progress to complete blindness if the deficiency is not addressed.² Further, it is also involved in the formation of cells in the structure of the eye, such as the cornea and conjunctiva. Deficiency of vitamin A can also lead to dry eyes, as the cells around the cornea lose their ability to produce sufficient mucous.²

Other functions of Vitamin A include helping to support healthy foetal growth, though we need just the right amount, as too much could be associated with a risk of birth defects. Vitamin A also helps maintain the health of our skin and organ lining² (you may have heard of some acne treatments which are, essentially, very high dose vitamin A).² Some evidence suggests an immune supportive role for vitamin A,³ by way of maintaining healthy function of immune cells such as T-cells, natural killer cells and monocytes.²

How much do we need? The recommended dietary intake (RDI) for men is 900mcg retinol equivalents per day and for women the RDI is 700mcg retinol equivalents per day. This increases to 800mcg retinol equivalents in pregnancy for women over the age of 18.¹ The maximum limit in pregnancy is 3000mcg retinol equivalents.

Vitamin B1 (Thiamin)

This nutrient was first isolated from rice bran in 1911 by Casimir Funk. He called it a “vitamine” because it was an amine and he felt that it was vital to our health.⁴ Since then the “e” has been dropped off the end, creating the modern term “vitamin”. The best source of Vitamin B1 is brewer’s yeast, lean meat and legumes, with some amounts also being found in grains and soy milk.⁵

Like most of the other B-vitamins, vitamin B1 (also called Thiamin or Thiamine) is involved in the metabolism of carbohydrates, proteins and fats as a cofactor. As such, it helps to turn our food into energy. Vitamin B1 is also required for the production of neurotransmitters, as well as nerve transmission and deficiency of this nutrient impacts the brain’s ability to use glucose for energy.⁵ A thiamin deficiency, if severe, can cause extreme health problems. We only need between 1.1mg (women) and 1.2mg (men) per day,⁶ but unfortunately it can be common for the elderly or those with very low dietary intake to become deficient in this nutrient.⁵

Vitamin B2 (Riboflavin)

Vitamin B2 was discovered in 1917 and is a water-soluble vitamin (as are all the B’s), which is found in milk and milk products, as well as eggs, legumes, organ meats, almonds, wild rice and mushrooms. It’s heat resistant, meaning that cooking does not significantly affect a food’s riboflavin content, though it is more easily absorbable from fresh foods.⁷ The recommended daily intake for Vitamin B2/Riboflavin for ages 19 – 70yrs old is 1.1mg per day for women and 1.3mg per day for men and for people over 70yrs old 1.6mg per day for men and 1.3mg per day for women.⁸

Riboflavin has a variety of functions, including turning our food into energy. It is also required to activate vitamins B6 and folate, and it is necessary for facilitating immune function, tissue repair and hair, skin and nail growth.⁷ It has been used to help prevent migraines, with high dose Riboflavin having been shown to be beneficial in reducing the frequency of migraine headaches.⁹ In a study involving 55 patients, 59% of the treatment group had at least a 50% improvement in migraine frequency when compared to the placebo group. Another clinical trial involving 23 patients confirmed this result with a reduction of migraines per month from 4 days to 2 days.⁹

This nutrient may also help to prevent free radical damage and work synergistically with Vitamin E, by preventing the oxidation of this nutrient.⁹

Vitamin B3 (Niacin/Nicotinic Acid)

Vitamin B3 is often used in the forms of nicotinic acid and nicotinamide, which are very closely related to niacin and act very similarly. The best sources of this nutrient are beef, pork, wholegrains, eggs and cow’s milk, with the niacin in meat products being more bio-available than, for instance, the niacin from grains.¹⁰

Vitamin B3 is a cofactor in both energy production and DNA repair. It may also help to lower blood fats and bad cholesterol and it is thought that it may do this by reducing the release of free fatty acids from fatty tissue, which consequently reduces production of VLDL cholesterol. Another theory is that B3 directly reduces low density lipoprotein (bad cholesterol) production in the liver.¹¹

Recommended daily intake for this vitamin is 14mg for women and 16mg for men,¹⁰ with a balanced, healthy diet generally supplying adequate amounts.

Vitamin B5 (Pantothenic Acid)

Unlike some of the other vitamins, Vitamin B5 is very sensitive to heat, freezing and processing. Good sources of this nutrient are meats, legumes, egg yolk and potatoes. Grains, broccoli, avocado, mushrooms and apricots also contain some B5. Unfortunately, the cooking process can diminish Pantothenic acid levels in food by up to 50%.¹²

Pantothenic acid is necessary for our bodies to be able to metabolise carbohydrates, proteins and fats and turn them into energy. It is also essential in stress management as it is needed for healthy adrenal function and cortisol production. We also need vitamin B5 for our bodies to be able to produce other necessary compounds such as bile acids, vitamin D, steroid hormones and ubiquinone (CoQ10).¹² It may also support wound healing, with some animal studies indicating increased wound closure and stronger scar tissue after oral and topical Pantothenic Acid treatment.¹²

A daily intake of 4mg for women and 6mg for men is suggested daily.¹²

Vitamin B6

You will sometimes find this nutrient in supplements in the form of Pyridoxal-5-phosphate (PLP), which is the form most common in our body.¹³ Vitamin B6 is generally quite well absorbed, with a bioavailability of about 75% from a balanced diet. It’s found in quite a variety of foods, including meats such as chicken, beef and fish, wholegrains, legumes, vegetables and fruits.¹⁴ Cooking and processing diminishes vitamin B6 content in foods by about 40%, though it may be up to 70% according to some literature.¹⁴

We need this nutrient for the metabolism of amino acids¹⁴ (the building blocks that make up protein). B6 is also necessary for serotonin, dopamine and GABA production, immune system function and hormone modulation amongst other functions.¹⁴ It is commonly used in the management of PMS symptoms, a use which is supported by clinical trials at doses of up to 100mg daily.¹⁴ Another benefit of vitamin B6 is the relief of morning sickness in pregnancy. A review of clinical trials has found that B6 is mostly effective in reducing nausea in early pregnancy. The supplement seems to take effect between 3 days and 3 weeks of treatment.¹⁴

Daily requirements of this nutrient is between 1.3mg and 1.5mg for women and between 1.3mg and 1.7mg for men, with deficiency being rare.¹³ In pregnancy the recommended daily dose is 1.9mg per day.


Vitamin B12

The active form of Vitamin B12 is called methyl cobalamin¹⁵ and we need it for the formation of red blood cells in bone marrow. It is also involved in the growth and replication of all cells.¹⁶ This vitamin is also essential for keeping homocysteine levels down by supporting its conversion to methionine.¹⁶ Dysfunction of this pathway can lead to further health problems.

Another function of vitamin B12 is the formation of protein structures that make up the myelin sheath and nerve cells,¹⁶ hence we need it for proper nervous system and brain function. It is also required for healthy immune system function.¹⁶

Clinically, vitamin B12 may be used to help with energy, along with the other B-vitamins and it may also help to protect and support the cardiovascular system due to its role in homocysteine metabolism. There is also some literature to support its use in assisting brain function. Another interesting use of vitamin B12 is the addition of this nutrient to a cream to use topically to help manage dermatitis. A study has shown it to be beneficial in reducing the severity of this condition when applied twice daily.¹⁶

The best sources of B12 are meat and dairy products¹⁵, i.e. animal products. Bioavailability varies between sources and absorption also tends to decrease with increasing intake.¹⁶ in other words, your body tends to absorb what it needs to saturate the absorption sites. So how much vitamin B12 should we be getting every day? We only need about 2.4mcg daily¹⁵, but even so, deficiency can be fairly common amongst the elderly.¹⁶ Those who are on vegan or vegetarian diets may also be at risk of deficiency.


The terms folate and folic acid are often used interchangeably, though there is actually a slight difference. Folate is the nutrient which occurs naturally in foods, folic acid is the synthetic form used in supplements and to fortify foods.¹⁷ Folate is well known for its role in preventing Neural Tube Defects in infants due to its role in supporting closure of the neural tube. It is also required for DNA and RNA formation and repair.¹⁷ It helps to activate vitamin B12 and works together with it to maintain healthy homocysteine levels. Further, it plays a role in the metabolism of some amino acids, such as glycine and histidine.¹⁸

Good sources of folate include dark green leafy vegetables, such as spinach, kale, mustard greens and radicchio. It is also available in lentils, asparagus, broccoli and cauliflower.¹⁷ Cooking diminishes a large portion, if not most of the folate in foods, making raw foods favourable sources of this nutrient.¹⁸ The recommended daily intake is 400mcg daily for adults, and this requirement increases to 600mcg daily during pregnancy. Deficiency of this nutrient is fairly common and it doesn’t take long to develop – we can become deficient within 4 months.¹⁸ Therefore, regular intake of green leafy veg and other raw food sources of folate is important to maintaining our folate levels and our health.


Biotin is part of the B-group vitamins and as such also helps to facilitate the process of turning food into energy.¹⁹ It is often referred to in terms of hair, skin and nail health as it is involved in the maintenance of these and a biotin deficiency can lead to hair loss.²⁰ Some studies have found it to be helpful in strengthening fingernails of women with brittle nails.¹⁹ It is also helpful for liver function,²⁰ while some research suggested it may also have a role in the replication of DNA.¹⁹

Although possible, biotin deficiency is quite rare.²¹ The adequate dietary intake is around 25mcg per day for women and 30mcg per day for men and it can be obtained from bean sprouts, egg yolk, milk, wholegrains, soy and some organ meats like kidney and liver. Small amounts of biotin are also produced by the good bacteria in our gut.²⁰ 

Vitamin C (ascorbic acid)

Vitamin C is well known for its role in modulating immune function, but this nutrient has many other critical functions in the body as well. It is an essential component of collagen production²² making it helpful in maintaining healthy skin. It helps us to absorb iron and copper, and it is also involved in cholesterol metabolism, the synthesis of neurotransmitters and the formation of thyroid hormone.²²

Ascorbic acid is one of the antioxidant vitamins, and it helps to prevent free radical damage both directly, by scavenging free radicals itself, and indirectly, by regenerating vitamin E, another antioxidant vitamin.²² Vitamin C also helps to metabolise histamine and studies have shown that higher serum vitamin C levels are associated with lower serum histamine, ²² making this a helpful nutrient for hay fever sufferers.  

Another function for which ascorbic acid is often overlooked is the role it plays in bone formation and maintenance. Research has shown that a positive association exists between vitamin C in the diet and serum and bone mineral density, i.e. people with higher levels of vitamin C generally had better bone mineral density.²²

The recommended daily intake for this nutrient is 45mg per day, with the best sources being a variety of fruit and vegetables. These include blackcurrants, guava, citrus fruit, capsicum, kiwi fruit and broccoli, among others.²³

Vitamin D

Vitamin D is a fat soluble vitamin which is predominantly synthesised in our skin, and is then activated by exposure to sunlight, or, more specifically, the ultraviolet light from the sun. This activation is necessary for our bodies to be able to utilize the vitamin D. Some foods provide small amounts of this nutrient, such as cod liver oil, fatty fish and beef.²⁴ One of the functions of vitamin D (also referred to as colecalciferol) is the regulation of calcium homeostasis and bone formation. It plays a part in the synthesis of osteocalcin, a compound involved in bone modelling/remodelling.²⁴ Further, it is also involved in maintaining healthy muscle function, as well as helping with immune regulation. It supports macrophage activity, as well as modulating the response of various other immune factors and cells.²⁴

More recent research has revealed that we need vitamin D for healthy brain homeostasis as well, ²⁴ with two studies also finding that vitamin D may have beneficial effects on modulating mood.²⁵ In addition to this, two further studies have found that there is an association between cognitive decline and vitamin D levels, with those who are deficient in this nutrient being at a higher risk of reduced mental functioning.²⁶

The recommended daily amount is about 400IU²⁷ and deficiency is fairly common, with close to 25% of the population having insufficient vitamin D levels.²⁸ Rates tend to be highest during winter, especially in Victoria and the ACT, while the Elderly seem to be particularly at risk.²⁸

Vitamin E

This nutrient was first discovered in 1922 in the United States and its main action is as an antioxidant.²⁹ It helps to protect fatty acids from oxidation. Vitamin E is the collective term for a group of eight compounds, four of which are called tocopherols and four are tocotrienols. ³⁰ The highest amounts of tocopherols are in soy bean oil, olive oil, corn oil and sunflower oil, while tocotrienols are abundant in palm oil, coconut oil and cocoa butter. Some Vitamin E can also be obtained from other food sources, such as nuts and seeds, spinach, kale, sweet potatoes and egg yolks.²⁹

In addition to its antioxidant function, Vitamin E also plays a role in maintaining the healthy function of our immune system. It can be beneficial in supporting cardiovascular health, largely due to its ability to neutralize free radicals and reduce oxidant damage. Studies have also shown Vitamin E to be helpful in supporting healthy blood pressure. One study showed a decrease in systolic blood pressure or 24% in patients with mild hypertension. This was after long term supplementation with vitamin E.²⁹

When it comes to nutritional requirements, there is not enough evidence available to set a recommended dietary intake. In fact, it would seem that the required amount of vitamin E varies from person to person and is dependent on the amount and type of fat consumed in the diet. An adequate intake is used as a guide instead, and for vitamin E this guide is around 7mg per day of alpha-tocopherol.²⁹

Vitamin K

There are two forms of this vitamin – Vitamin K1 (phylloquinone) and vitamin K2 (the term for substances called menaquinones).³¹ Green leafy vegetables, olive oil and soy bean oil are a good source of vitamin K1, while chicken, butter, egg yolks, cheese and fermented soybeans provide vitamin K2.³² This nutrient plays an important role in bone health, in that it is required for two of the proteins in bone – osteocalcin and matrix Gla Protein. The osteocalcin seems to help in the regulation of bone mineralization.³¹ There are studies to show vitamin K supplementation helps to reduce the incidence of fractures. This effect is potentially due to Vitamin K having a strengthening effect on the bone.³²

Vitamin K is also involved in our clotting ability. It is a precursor to the enzymes that convert inactive precursors into active clotting factors, which are then secreted into the blood by our liver cells. Interestingly, vitamin K supplements do not seem to affect blood clotting in the absence of deficiency. ³¹

The adequate intake of vitamin K is considered to be around 90mcg daily. ³¹

Before starting on any new vitamin supplements, please consult with your healthcare practitioner to see if they are suitable for you. Remember that vitamin and mineral supplements can only be of assistance if the dietary vitamin intake is inadequate.


3. Hendler, SS & Rorvik, DM, 2008, “PDR for Nutritional Supplements – 2nd Edition”, Chapter: Vitamin A, pp. 627 – 634, Thomson-Reuters, Montvale USA.

9. Hendler SS & Rorvik DM, 2008, “PDR for Nutritional Supplements – 2nd Edition”, Chapter: Riboflavin, pp. 547 – 553, Thomson-Reuters, Montvale USA.

12. Braun, L & Cohen, M. 2015, “Herbs and Natural Supplements, 4th Edition”, Chapter: Vitamin B5, pp. 1070 - 1078, Churchill Livingstone, Chatswood NSW, Australia

14. Braun, L & Cohen, M. 2015, “Herbs and Natural Supplements, 4th Edition”, Chapter: Vitamin B6, pp. 1078 - 1091, Churchill Livingstone, Chatswood NSW, Australia

16. Braun, L & Cohen, M. 2015, “Herbs and Natural Supplements, 4th Edition”, Chapter: Vitamin B12, pp.1091 - 1101, Churchill Livingstone, Chatswood NSW, Australia

19. Hendler SS & Rorvik DM, 2008, “PDR for Nutritional Supplements – 2nd Edition”, Chapter: Biotin, pp. 84 - 89, Thomson-Reuters, Montvale USA.

22. Braun, L & Cohen, M. 2015, “Herbs and Natural Supplements, 4th Edition”, Chapter: Vitamin C, pp. 1101 - 1124, Churchill Livingstone, Chatswood NSW, Australia

24. Braun, L & Cohen, M. 2015, “Herbs and Natural Supplements, 4th Edition”, Chapter: Vitamin D, pp. 1125 - 1149, Churchill Livingstone, Chatswood NSW, Australia

25. Hendler SS & Rorvik DM, 2008, “PDR for Nutritional Supplements – 2nd Edition”, Chapter: Vitamin D, pp. 669 - 681, Thomson-Reuters, Montvale USA.

26. Soni, M, Kos K, Lang IA et al. 2012, “Vitamin D and cognitive function”, Scandinavian Journal of Clinical and Laboratory Investigation, Vol. 72(sup243), pp. 79 – 82.

29. Braun, L & Cohen, M. 2015, “Herbs and Natural Supplements, 4th Edition”, Chapter: Vitamin E, pp. 1149 - 1176, Churchill Livingstone, Chatswood NSW, Australia

32. Dinicolantonio JJ, Bhutani J & O’Keefe JH, 2015, “The health benefits of vitamin K”, Open Heart, Vol 2, cited on 12/10/2018,