Published on 23rd September 2016


With the UK’s nutritional supplement market valued at £431m and one leading high street retailer of nutritional supplements and health foods forecasting a growth in sales to £1bn per annum by 2020,1,2 Lisa Patient looks at when — or whether — we really need to top up our diet

In a perfect, stress-free world we would all be optimally nourished from our diet and have an abundance of energy and joie de vivre. We would rarely suffer from disease, and medication or supplementation would be completely unnecessary. Yet many of us turn to popping pills and swigging solutions in order to make up for nutritional shortfalls, often in the hope that it will make us feel good and — even better — help us live well and for longer. But how do we know whether we need supplements, or even if they really do what they claim?


The regulation of vitamin and mineral supplements in the UK is currently governed by an EU Directive that classifies them as food supplements. These are defined as: “any food the purpose of which is to supplement the normal diet and which a) is a concentrated source of a vitamin or mineral or other substance with a nutritional or physiological effect, alone or in combination; and b) is sold in dose form”.3

If a product is claimed to treat or prevent disease, or can be taken with a view to restoring, correcting or modifying a physiological function, then it becomes classified as a medicinal product, and is subject to a different set of legislation and strict safety tests. To get round this, a supplement label is likely to say, for example: ‘a combination of nutrients to support liver function’ rather than ‘improves liver function’. Products containing herbs are also regulated under a separate EU directive (Directive 2004/24/EC ).

Supplements can be in liquid, capsule or powder form, and because they are classified as food supplements they are subject to food legislation, including labelling and use-by dates.4

Chemical combinations
The EU directive includes a list of the chemical formulas of nutrients that can be included in a food supplement. For example, there are no fewer than 20 formulations of the mineral calcium on the list, including calcium carbonate, calcium citrate and calcium citrate malate. This information is important because each formula has a different level of bioavailability, which is the amount that is actually absorbed into the blood stream, affecting both efficacy and price.(A nutritional therapist should advise on factors such as bioavailability if recommending supplements.)

Many experts argue that if we eat a varied diet then we should not need to take supplements. But in some instances, we may not be getting all the nutrients we need — particularly if following a restricted diet; for example a vegan diet does not contain vitamin B12, except in fortified foods. In such cases, a nutritional therapy approach would be to use supplements in a targeted way, but alongside making appropriate changes to diet.

Common deficiencies
Some vitamin and mineral deficiencies are acknowledged by the medical profession to be factors in ill health, and so blood tests to check for deficiencies can be arranged with a GP, through a nutritional therapist or privately, with GPs following the testing and prescribing guidance set by the National Institute for Health and Care Excellence (NICE).

The most commonly-run tests are for deficiencies in iron, folate, calcium, vitamin B12, sodium and potassium. Fatigue and low energy could point to iron, folic acid and/or vitamin B12 anaemia.

Iron is used to make the red blood cells that carry oxygen around the blood, so if iron is low, energy production will be low. In the case of iron deficiency anaemia, a GP will typically prescribe a daily dose of 100 to 200 mg, usually in the form of dried ferrous sulphate. This can have side effects such as nausea, diarrhoea or constipation; so iron is commercially available as drops which minimise the impact on the digestive system. However, too much iron can be toxic, so levels should be monitored.

Vitamin B9 is also used for energy production. It is found naturally in plant foods as folate, and in supplements as folic acid. It is vital for healthy development of embryos, and prevention of neural tube defects. Women planning pregnancy are advised to take 400 micrograms (µg) daily before pregnancy and throughout the first 12 weeks, even if they are already eating foods fortified with folic acid or rich in folate. A recent development is supplementation in the form of folic acid called methylfolate, (a biologically active form) which may be beneficial to people who do not have the genes to utilise inactive folic acid.

The NHS protocol for vitamin B12 anaemia is to administer injections (usually 1 mg three times a week for two weeks, then 1 mg every three months), as the anaemia may be due to the patient not sufficiently absorbing B12 from food. This is a very high dose compared to that available in supplements, and long term use of high amounts of vitamin B12 can cause side effects such as headaches and dizziness. As this vitamin is found in very few non-animal sources, it is a nutrient that vegans and vegetarians may need to supplement. It is often combined with an enzyme called intrinsic factor to help absorption, or as a liquid that is absorbed into the bloodstream under the tongue.

GPs have become increasingly aware of vitamin D deficiency and, more recently, would test patients in an ‘at risk’ group (infants and children aged under five; pregnant and breastfeeding women; people aged over 65; people who have low or no exposure to the sun and people with darker skin). However, in July this year, Public Health England advised that everyone should take supplements during the autumn and winter months because of the lack of sunlight, which our body uses to make vitamin D. Although this was announced in England and Wales, the advice would naturally be relevant to the entire British Isles and other northern countries which have low levels of sunlight.

For a severe deficiency, a GP may prescribe a high-dose vitamin D supplement. For moderate deficiency, an over-the-counter supplement should be sufficient. A combination of vitamin D and calcium may typically be prescribed to post-menopausal women to protect their bones and as a precautionary measure in the prevention of osteoporosis. (See The Vitamin D Debate, page 18.) In the case of the two major electrolytes, sodium and potassium, these may be tested to check kidney function. These two minerals maintain the important balance of fluids inside and outside of the cells. Sodium may become depleted when you do strenuous exercise or sweat profusely, and potassium can be depleted if you have a diet low in plant foods or have a heart condition. 
It is not recommended that these nutrients be supplemented without medical advice, because high levels of either can disturb the body’s fine electrolyte balance and cause serious health complications.

Private testing

A number of private laboratories offer combinations of blood or urine tests to assess vitamin and mineral deficiencies, however most are only accessible to the public via a health professional such as a nutritional therapist.

Minerals such as chromium, copper, magnesium, iodine, molybdenum, selenium and zinc are tested using a combination of blood and urine. Hair analysis is also used by some complementary health practitioners to obtain a snapshot of mineral levels at a certain time from the amount excreted in the hair.

Those vitamins that dissolve into fat, including vitamins A, D and E, can be measured in blood samples, but others such as B vitamins are typically measured by looking at the concentration of certain enzymes in the blood. The B vitamins activate these enzymes, and if there is insufficient quantity of enzymes there is likely to be a greater need for the B vitamin.

Reference ranges

One difference between NHS and private testing is in the quoted optimal reference ranges. These are the values that are used to determine whether or not supplementation is necessary. Most UK laboratories use the same ranges as the NHS, which are regularly reviewed by the National Diet and Nutrition Survey.5 However if you use an overseas laboratory, the values may be different due to the quality of diet in that country. In the case of vitamin D, most private laboratories now believe that there is sufficient evidence for higher optimal values of vitamin D than set by the NHS.

NRVs and dosage

For many years we lived with RDAs (recommended daily allowances) as a guide to how much of a nutrient we require per day to stay healthy. In December 2014, following an EU directive to make labelling more simple, this was replaced by Nutrient Reference Values, or NRVs.6

NRVs are designed to guide you on how much of a nutrient you need as a daily minimum to maintain good health, but not the dose you would need from a supplement to correct a deficiency or to use therapeutically. In fact, most of us who eat a balanced diet would easily achieve the NRVs from our food alone.

“When buying supplements it’s tempting to choose the strongest dose, but bigger is not always better”

What to buy
When buying supplements it’s tempting to choose the strongest dose, but bigger is not always better. In fact, extreme caution should be taken when using high doses of vitamins and minerals, because many can be toxic or have unpleasant side effects. The European Food Safety Authority has published a ‘tolerable upper intake level’ for vitamins and minerals, above which there is a likelihood of adverse side effects.

And it is possible to experience problems if you are supplementing on top of a nutrient-rich diet.7 Recent studies have found that long-term intake of the mineral chromium, a popular ingredient in weight-loss supplements, may cause production of carcinogenic chemicals within our cells, and that excess iodine can interfere with thyroid function.8,9 A study in 2014 found that supplementation of vitamin E and selenium were linked to an increased risk of prostate cancer.10 Product packaging will tell you that vitamin C is a laxative in high doses, and long term intake of 10 mg or more of vitamin B6 can lead to tingling and numbness.

It is because of such potential side effects that it is recommended to consult a GP or qualified nutritional therapist who can assess your needs and advise a programme from a reputable supplier and at the right dose. But eating a balanced, healthy diet should always be the place to start.

Finally, when it comes to buying products online, buyer beware! There are plenty of unregulated products that make promises, but they should be avoided. Aside from the potential risk to your health, you may be buying nothing but so-called snake oil and throwing your money away.



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  8. Wu LE et al (2015). Carcinogenic chromium (VI) compounds formed by intracellular oxidation of chromium (III) dietary supplements by adipocytes. Angewandte Chemie Int. Ed., 2015; DOI: 10.1002/anie.201509065.
  9. Leung AM & Braverman LE (2013). Consequences of excess iodine. Nat Rev Endocrinol. 2014 Mar; 10(3): 136–142.
  10. Kristal AR et al (2014). Baseline selenium status and effects of selenium and vitamin E supplementation on prostate cancer risk. J Nat Cancer Inst., Feb 2014 DOI: 10.1093/jnci/djt456.