Ever since vitamins were discovered to be important to maintain health and well-being the controversial question that has been asked is how much vitamins does my body need? Even different countries and international authorities cannot agree on standardised daily amounts of vitamins and minerals one needs.
Then there are other groups and researchers who recommend intakes that are so high that they could never be achieved by diet alone. This movement of advocating mega doses of vitamins was originally started by Linus Pauling, the Nobel prize-winning chemist, who recommended doses of vitamin C up to 100 times the estimated daily dose to treat infections like the common cold. And he has legions of supporters who swear that this approach helps to prevent and treat colds, although countless well-controlled studies have failed to show any such benefit from supplementation with large doses of vitamin C.
Is there any justification for taking amounts that exceed the requirements of the body?
The answer should technically be no, but there are several complicating factors.
There can be many different measures of a physiological requirement. For instance, it is well proven that you only need 10mg per day of vitamin C to prevent the development of scurvy. (Scurvy is the fatal vitamin C deficiency disease that killed off hundreds of thousands of sailors throughout the centuries before it was demonstrated conclusively in 1794 that the provision of fresh lemon or lime juice on long sea journeys could totally prevent this dreaded disease, although no one knew why until over 100 years later)
However, 10mg of vitamin C a day is not enough to promote effective wound healing. This only occurs at a minimum of 20mg per day. And if you were to use the optimum activity of immune function as the physiological yardstick then much higher daily amounts are required. A 100mg dose will usually lead to the total saturation of body tissues and so anything more than this amount will simply be excreted in the urine. The estimated adult male daily requirement for vitamin C has been set at 90mg/day in South Africa, 60mg/day in America and 40mg/day in Britain.
The Vitamin C Requirement for Each Person Is Different
There are other complicating factors that could raise the requirements further for certain individuals. This is because people have differing daily requirements, based on factors such as weight, activity levels and genetic make-up, and what would be adequate for one person might be totally deficient for another.
Rapid growing periods such as adolescence and pregnancy also raise intake requirements, as does old age due to declining levels of absorption. In addition various stresses, such as psychological stress or physical stress in the form of an illness or trauma (such as burns or surgery) can raise the requirements of vitamin C, for example, quite substantially, in which case even 100mg/day may not be sufficient.
Why Take Vitamin C Supplements?
The proponents of mega doses of vitamin C point out that humans, apes and guinea pigs are the only mammals that cannot make their own vitamin C. A rabbit for instance makes approximately 100mg vitamin C each day for every kilogram it weighs. If this were extrapolated to humans a 70kg person would require an incredible 7 grams a day.
From an evolutionary point of view, it doesn’t make sense for humans, apes and guinea pigs to be in the situation in which they cannot make vitamin C but are dependent on amounts that cannot be physically supplied through diet alone. Vitamin C was after all only first manufactured in commercial quantities in 1935 and humans, apes and guinea pigs have certainly managed to survive and reproduce (one could say too effectively) up until the advent of vitamin C tablets.
How Much Vitamins and Minerals Do I Need?
It has been said that ‘there is no such thing as a poison merely a poisonous dose’ and this adage could well apply to vitamins. Because something is essential in small amounts, as is the case with vitamins, it should never be assumed that it would be even better in larger amounts.
This is particularly relevant regarding the fat-soluble vitamins, like Vitamin A and vitamin D, as these are stored by the body and can therefore quickly build up to toxic levels. For instance, while vitamin A is essential for normal foetal development it can cause foetal abnormalities if the pregnant mother consumes it in excess (over 3300 micrograms/day).
Water-soluble vitamins are considered harmless as excess requirements appear to be simply excreted in the urine. Accumulating research indicates that this may not always be the case and safe upper limits have therefore been set for water-soluble vitamins (vitamins B and C).
Controversial research suggests that no more than 500mg/day of vitamin C should be consumed as above this amount there is a measurable increase in markers of genetic damage. This is being hotly disputed, but it does suggest that mega doses of vitamins may not be sensible and could be associated with undesirable side effects. Several studies involving high-dose beta-carotene supplements and smokers were abandoned when it became clear that the group taking the supplements showed an increased risk of developing cancer, particularly lung cancer.
For every essential nutrient there is a range of intakes between that which is inadequate leading to clinical deficiency disease and that which is in excess of the body’s metabolic capacity that there may be signs of toxicity. All the essential nutrients have many inter-dependent functions and taking large doses of one nutrient may skew or interfere with the functions of the other nutrients.
It is therefore recommended that people take balanced multi-vitamin supplements that are no more than 2-3 times the recommended daily amount (RDA) values and avoid large doses of single nutrients. This is especially important regarding minerals as they can become toxic at low levels.
For instance, the RDA for selenium is 55 micrograms/day. Research shows that supplements containing 200micrograms/day are safe and therapeutic but that signs of toxicity can result from as little as 800micrograms/day.
Equally zinc supplement have a beneficial effect on immune function at dosages up to 30milligrams/day but above 50mg/day start to harm immune function.
The best advice is therefore to take balanced lower-dose supplements to ensure that your health is not compromised by deficiencies or excesses.
Linda McCourt (MSc Nutritional Medicine)
This article was sponsored by McNab’s Vitamin Company as part of its educational campaign to promote responsible nutrition. Tel 011 646 9572
The table below provides the South African Recommended Daily Allowances (RDAs) of the main essential nutrients for women between 19-50 years. The values for men between 19-50 years are supplied in brackets. RDA values vary with age and sex. The safe Upper Limit (UL) indicates the maximum amount that should be taken- this value has not been determined for all nutrients. Amounts are in milligrams (mg) or micrograms (mcg).
|Vitamin||RDA||Safe UL||Mineral||RDA||Safe UL|
|Vitamin B1 (Thiamine)||1.1(1.2)mg||Magnesium||320(420)mg|
|Vitamin B2 (Riboflavin)||1.1(1.3)mg||Iron||18(8)mg||45mg|
|Vitamin B3 (Nicotinic acid)||14(16)mg||35mg||Zinc||8(11)mg||40mg|
|Vitamin B6 (Pyridoxine)||1.3(1.3)mg||100mg||Iodine||150(150)mcg||1100mcg|
|Vitamin B12 (Cobalamin)||2.4(2.4)mcg||Selenium||55(55)mcg||400mcg|