Vitamins - how much do we need? |
Our understanding of vitamins has come a long way in the
two centuries since an English naval doctor showed that adding citrus fruit to
sailor's diets could prevent scurvy. |
What are vitamins? |
The word vitamin is derived from the term 'vital amine',
given to vitamins by the scientists who discovered them and who believed they
were chemicals called amines.
We now define vitamins as any group of substances necessary in very small
amounts for healthy growth and development. We know that because they cannot be
synthesised in the body they are essential constituents of our diet. They fall
into two groups: those that are water-soluble (including the vitamin B complex
and vitamin C), and those that are fat-soluble (including vitamins A, D, E and
K). |
Vitamin requirements. |
What vitamins do, and where they are to be found, is
well-documented in both consumer and professional publications14. But beliefs about how much of each vitamin we need to
remain healthy have changed in recent years. Out are the recommended daily
allowances (RDA) and in is official recognition that we are all different and
may, therefore, have different vitamin requirements. In 1991, a report by the
Committee on Medical Aspects of Food Policy, from the Panel on Dietary Reference
Values, introduced four new measures of vitamin requirements 5.
- Estimated average requirement (EAR) - the average
requirement or need for food energy or a nutrient. Some people will need more,
others less.
- Reference nutrient intake (RNI) - an amount of a nutrient that will be
sufficient for almost everyone, even someone with a high need for that nutrient.
RNI is equivalent to the old RDA.
- Lower reference nutrient intake - an amount of a nutrient that is enough
only for those with low needs, so it is likely to be insufficient for most
people. Anyone having less than the LRNI will almost certainly be deficient.
- Safe intake - this indicates the intake of a nutrient for which there is not
enough information on which to base an estimate of our requirements. A safe
intake is one that is judged to be 'adequate' for almost everyone's needs but
not large enough to cause undesirable effects.
The UK now has to comply with European Union legislation and all vitamin
supplements must have European recommended daily allowances (ROA) on their
labels. Many believe that these ROA have little scientific value and debate
continues in Europe. The Department of Health has steered clear of making many
recommendations regarding vitamins, with the exception of folic acid (see Box 1)
and vitamins A and D supplements for babies of more than six months for whom
breast-milk is the main source of nutrition 6. The
official view is that most people get enough vitamins from their diet and it is
a matter for their doctor if they do not. (See Box 2 for a list of people who
may require a higher vitamin uptake). |
Box 1. Folic acid update. |
Folic acid is known to help prevent neural tube defects
such as spina bifida, and the Department of Health recommends that women
planning a pregnancy take folic acid tablets as a supplement and continue taking
them until the 12th week of pregnancy9. The DoH also
encourages women to eat foods rich in folic acid. However, research published in
March 1995 suggests that, compared with supplements and fortified food,
consumption of extra folate as natural food folate is relatively ineffective in
increasing folate status. The researchers believe that 'advice to womm, to
consume folate-rich foods as a means to optimise folate status is misleading'
10.
For more information on spina bifida contact: Association for Spina Bifida
and Hydrocephalus, ASBAH House, 42 Park Road, Peterborough, PE1
2UQ. |
Box 2. Extra needs. |
The following groups may need extra
vitamins: - Those on restricted diets, for instance people with diabetes,
vegans, people with coeliac disease, people with allergies.
- People with poor
appetites; for example, frail older patients, those who are ill; people who do
not eat a wide range of foods; for example, faddy children.
- Those
convalescing from illness.
- People with a weakened immune system.
- People
with digestive disorders.
- Menstruating women.
- Pregnant and breast-feeding
women.
- Slimmers whose reduced calorie intake has led to poorer nutrient
levels.
- Smokers and drinkers.
- Athletes and very active
people.
| |
Yet in the UK we spend more than 100m a year on vitamin and
mineral supplements 7. Fears about the quality of our
food and a belief that taking supplements is a good preventative measure are
both factors that influence our decision to take such supplements. The
Consumer's Association takes the view that most people do not need them but
those who wish to take extra vitamins should take a good multivitamin supplement
7.
According to Walji, a multivitamin tablet or capsule should contain: Vitamin
A, beta carotene, vitamins C,D,E and the minerals phosphorus, calcium,
magnesium, potassium, iron, zinc, manganese, copper, iodine, molybdenum,
chromium, selenium, vanadium choline, inositol, methionine, PABA, bioflavinoid,
lysine, lecithin, rutin, betaine, hesperdine and cysteine 2. Possible benefits of taking a multivitamin supplement
include 1: - Maintaining good general
health
- Ensuring adequate vitamin intake when on a restricted
diet
- Improving resistance to minor illness.
|
Choosing a supplement. |
Simply swallowing a multivitamin does not mean you will
benefit from all the nutrients in the tablet. Poorly made supplements may pass
through the body without even dissolving.
An undesirable addition to vitamin supplements is sugar, yet many supplement
labels reveal that sugar, in some form or other, has been added. Checking the
label before purchasing a vitamin supplement is important for people with
particular medical conditions, such as diabetes, or those following a particular
diet, such as an anti-candida diet. |
Box 3. Recent
research. |
Vitamin E.
A study of 2002 patients with
coronary atherosclerosis showed that taking a daily high-dose vitamin E
supplement reduced the risk of heart attack by 75% 11.
Vitamin C.
A survey (unpublished), funded by the National Asthma
Campaign, of more than 2000 people aged between 18 and 70 suggests that the more
vitamin C that people eat, the better their lung
function. | |
Another source of controversy is high-potency vitamins.
Generally speaking, there is rarely any benefit in taking more than the RNI,
since the excess will either be excreted, if the vitamin is water-soluble, or
stored, if fat-soluble. Research on high-potency vitamins has shown they have
therapeutic value in some cases (see Box 3). Large doses of vitamins A and D can
produce toxic effects, including birth defects 8, and
can interfere with absorption of other nutrients 2.
Time-release supplements are also available. These allow the ingredients of a
vitamin tablet to trickle out of a binding matrix over a prolonged period. This
has some benefit when taking water-soluble vitamins, since they cannot be stored
in the body.
Some vitamin products are advertised as being 'natural' or 'organic', but
there is little that is naturao about the extraction and purification process
associated with vitamin manufacture, and such products are usually more
expensive. |
Recent
developments. |
Research continues into the particular health benefits of
vitamins for different diseases and conditions. In the past year, for example,
there has been research into vitamin E and coronary heart disease, and the
protective value of vitamin C for people with respiratory conditions such as
asthma (see Box 3).
This year may see more European debate relating to nutritional supplements,
as the European Union gears up to publish a discussion document aimed at finding
a way of harmonising this market (see Box 4).
© Joanna Trevelyan (1996) Nursing Standard 92, 22, 48-50.
References.
• 1 Dowden A, Lacey G The Consumer Guide to
Vitamins: How to Choose Vitamins, Minerals and Other Food Supplements.
London; Pan Books, 1996.
• 2 Walji H Vitamins, Minerals and Dietary
Supplements: A Definitive Guide to Healthy Eating. London; Headway,
1995.
• 3 Trimmer E The Good Health Food Guide: How
to Choose Health Foods and Supplements to Boost Your Health. London;
Piatkus, 1994.
• 4 Department of Health Eat Well: Action Plan
from the Nutrition Task Force to Achieve the Health of the Nation
Targets for Diet and Nutrition. London; DoH, 1994.
• 5 Department of Health Dietary Reference
Values for Food Energy and Nutrients for the United Kingdom. (Report of the
Panel on Dietary Reference Values of the Committee on Medical Aspects of Food
Policy.) London; HMSO, 1991.
• 6 Department of Health Weaning and the
Weaning Diet. (Report of the Working Group on the Weaning Diet of the Committee
on Medical Aspects of Food Policy.) London; HMSO, 1994.
• 7 Consumer's Association. Vitamins and Minerals.
Which? 1995; 8; 1; 1.
• 8 Rothman KJ, Moore LL, Singer MR et
al. Teratogenicity of high Vitamin A intake. New England Journal of
Medicine. 1995; 33; 21; 1369-1373.
• 9 Department of Health Folic Acid and the
Prevention of Neural Tube Defects. London; DoH, 1992
• 10 Cuskelly GJ, McNulty H, Scott JM. Effect of
increasing dietary foliate on redcell folate: implications for prevention of
neural tube defects. Lancet. 1995; 347; 657-659.
• 11 Stephens NG, Parsons A, Schofield PM et
al. Randomised controlled trial of vitamin E in patients with coronary
disease: Cambridge Heart Antioxidant Study (CHAOS). Lancet. 1996; 347;
781-786. |
Box 4. European
view. |
Last year fears receded in the UK that vitamins,
minerals and other nutritional supplements would need a full product licence in
order to comply with a European Union directive. It was decided that they fell
outside the remit of the directive because production techniques of the
supplements were different to those of medicines. More recently, member
states have become concerned that differences in the controls on dietary
supplements within the EU are causing increasing trade problems. According to a
spokesperson for the Ministry of Agriculture, Fisheries and Foods, the European
Commission has concluded that these problems have become sufficiently important
for it to consider how they might be dealt with. A discussion paper is being
prepared by the EC for consideration by member states but is unlikely to be
issued before the summer. MAFF will 'consult fully' before deciding the UK's
response. A ministry spokesperson said: 'In previous
discussions the UK made it clear that any strategy for dealing with the trade
problems associated with dietary supplements should not automatically lead to
regulation. The UK would wish to ensure that any EC proposals are proportionate
to the need. We would want to ensure that consumers are given as much choice as
possible in the area of dietary supplements, providing that public health is not
compromised.' | |
|
