Vitamins – What are they and why do we need them?

Friday, 16 November 2018

The early part of the 20th century was an exciting time for nutrition science. During this time, it was discovered that life and growth of animals required more than just carbohydrate, protein, fat, minerals and water. Vitamins are organic compounds that are involved in regulatory functions and are required in the diet as the human body is unable to make them.

There are 13 essential vitamins our bodies need to function optimally. Vitamins can be classified into two categories, water-soluble (B-complex and vitamin C) and fat-soluble (vitamins A, D, E and K). The body handles water-soluble vitamins differently from fat-soluble. Water-soluble vitamins are absorbed into the blood and cannot be retained for long periods by the body and are excreted in the urine whenever blood levels exceed kidney thresholds. The digestion and absorption of fat-soluble vitamins differs from that of the water-soluble vitamins. It requires the presence of bile salts and are better absorbed when consumed with dietary fats 2. Unlike the water-soluble vitamins, fat-soluble vitamins can also be stored in the liver and the body’s fat deposits until needed.

Apart from Vitamin C, all water-soluble vitamins form part of the B complex. Many of the B vitamins are involved in helping our bodies release the energy from the food we eat. An example of this is niacin. Niacin is an important vitamin and coenzyme that helps our body’s turn carbohydrate, fat and protein into energy. In general, if you are lacking in B vitamins, you may feel tired and lethargic.

For people living with diabetes, certain medications can affect the absorption of some B vitamins. One of the largest and longest (13 year follow up) studies of metformin treatment, the Diabetes Prevention Program Outcomes Study (DPPOS) 4 found that participants taking metformin had an increased risk of vitamin B12 deficiency. Vitamin B12 deficiency can lead to nerve problems (neuropathy) and anaemia (low red blood cell count) 4. Deficiency also increases the body’s concentration of homocysteine (a common amino acid) in your blood above recommended levels. When this occurs over a long time, it can increase your risk of developing heart disease.

To help maintain adequate vitamin B12 stores, ensure you are eating a varied and well balanced diet made up of lean red meat, chicken, seafood, whole eggs and, reduced fat dairy. An Accredited Practising Dietitian can help ensure your diet meets your vitamin B12 requirements. If you are taking metformin, it is recommended to get your vitamins B12 levels checked and monitored by your doctor and only supplement if advised.

There are four different fat soluble vitamins, vitamins A, D, E and K. As well as the water-soluble vitamins, all of the fat-soluble vitamins are required to allow the body to function optimally. A deficiency in one or more of these vitamins can lead to unpleasant symptoms. Consuming too much of these vitamins can also be toxic to the body and can harm your liver and other internal organs. It is unlikely that a person will overdose on a vitamin from the consumption of natural whole foods. The majority of cases of excessive vitamin intake reported were from taking a dietary supplement.

Vitamin D

Just under one in four (23% or 4 million) adults in Australia had vitamin D deficiency according to our latest national health survey 5. Vitamin D is essential for the body to absorb calcium effectively and vital for bone health and optimal muscle and nerve function. A deficiency can lead to osteopenia (bone loss) and eventually osteoporosis in adults and if severe, rickets in children.

Groups at increased risk of vitamin D deficiency include:

  • Elderly and those who spend most of their day indoors
  • Those with naturally dark skin
  • Those who avoid sun exposure for skin protection or due to medical advice for other medical conditions
  • Populations who cover their bodies for cultural or religious reasons
  • Populations that live > 35 degrees north or south of the equator (i.e. Tasmania, Melbourne)
  • Athletes who train long hours and compete primarily indoors (i.e. gymnasts)

Unfortunately food alone cannot provide enough vitamin D so the most reliant source is exposure to sunlight in particular, UVB light. Sun exposure times vary according to the season, location in Australia, skin type and, the how much skin is exposed. To find out more about how much sunlight you need for adequate vitamin D without skin damage, click here.

It is always advised that prior to taking any vitamin supplement, you seek expert advice from an Accredited Practising Dietitian (APD) or your doctor.


  1. Australian National Health and Medical Research Council & New Zealand Ministry of Health. (2018). Nutrient reference values for Australia and New Zealand. Retrieved from
  2. Gropper, S.S., Smith, J.L., & Grodd, J.L. (2009). Advanced Nutrition and Human Metabolism (5th). Wadsworth, Cengage Learning. Belmont, CA
  4. Aroda et al. (2016). Long-term Metformin Use and Vitamin B12 Deficiency in the Diabetes Prevention Program Outcomes Study. J Clin Endocrinol Metab, 101(4): 1754–1761
  5. (Vitamin D prevalence)


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