Most nutrition experts agree it’s usually unnecessary to take vitamin supplements if you’re eating a balanced diet that’s packed with a range of nutrients. But it’s not always easy to know just how much of each vitamin you need – or what the best food sources are.

That’s where Weight Loss Resources comes to the rescue with its definitive guide to vital vitamins. For each vitamin, we’ll tell you how much you need, what the best sources are and give you ideas on how you can meet your requirements each day.

Back to basics

Vitamins are often called micronutrients because they’re needed in such small quantities. Recommended amounts are given in milligrams (mg), equivalent to one thousandth of a gram, or micrograms (mcg), equivalent to one millionth of a gram. But even though we need such tiny amounts, vitamins are essential for good health and because the body can’t make them (with the exception of vitamin D and vitamin K, they need to be provided in the food we eat.

Most vitamins are known by a letter of the alphabet, although they also have a chemical name, for example, the chemical name for vitamin C is ascorbic acid. Vitamins can also be broadly classified into two groups – water-soluble vitamins (B group and C) and fat-soluble vitamins (A, D, E and K). Water-soluble vitamins are easily destroyed by high temperatures, light and processing, so it’s important that foods rich in these vitamins are eaten each day. In contrast, fat-soluble vitamins, which are generally found in foods with a high fat content, are more stable to heat and processing and can be stored in the body for long periods of time.

Recommended intakes

Our age, gender, body size, activity levels and lifestyle can all affect our nutritional needs for vitamins and so recommended intakes usually differ for men, women and children of different ages. For example, men tend to have higher requirements for most vitamins than women because they are bigger.

In the UK, recommended vitamin intakes for men, women and children of different ages are set by the Department of Health. The gold standard for each is called the Reference Nutrient Intake (or RNI) – formerly known as the recommended daily amount (RDA) or recommended daily intake (RDI). The RNI is considered to be enough to meet the requirements of most people and is generally more than most of us need. If you’re meeting the RNI, the risk of being deficient in a certain nutrient is very small.

Furthermore, the Department of Health also sets a Lower Reference Nutrient Intake (LRNI) for each vitamin. The LRNI is thought to be the amount that’s sufficient for just a few people with low requirements and most of us need more than this for good health. If you’re only meeting the LRNI – or are having less than this – there’s a good chance you may be deficient in that nutrient.

Finally, for some vitamins a ‘safe intake’ is set. This is used when there’s insufficient information to estimate a RNI or LRNI. It’s thought to be enough to meet the needs for almost everyone, without being so large that it causes unpleasant side effects.

So now you know the basics, here’s the low-down on each individual vitamin: how much you need each day, why you need it, good food sources, health problems associated with deficiency and overdose, and how to make sure you're getting enough in your diet.