Why food supplements can exceed your daily recommendations

Since 2007 despite the recession we’ve been spending more and more on vitamins. Last year we spent almost €16 million and Euromonitor expects our spend to increase by another 3 per cent in the next five years.

So it’s worth asking whether or not taking high dose vitamins, way above the recommended daily allowance, is necessarily a good way to spend our hard-earned cash.

At the moment, certain vitamins that exceed prescription doses can be sold over the counter if marketed as food supplements even though high doses of some vitamins can cause adverse side effects, interfere with other medicines and even increase mortality.

There are no maximum safe limits for vitamins and minerals used in food supplements or fortified food although this has been promised at EU level since the early 2000s.


Following the introduction of the European Communities (Food Supplements) Regulations 2007, the Irish Medicines Board (IMB) sought advice on the status of vitamins and was told by the Department of Health and Children that vitamins exceeding prescription dosage levels may be marketed as food supplements once no medicinal claim is made.

Prescription control
Vitamin B6, sometimes taken by women suffering from pre-menstrual tension, is subject to prescription control at doses over 50mg per day but doses of up to 100mg can be bought over the counter in some health food shops where it's sold as a food supplement.

The "tolerable upper limit" or UL for this vitamin, after which adverse effects may occur, is 25mg. The RDA or recommended daily allowance for this vitamin is less than 2mg per day. High intakes can cause bone pain, muscle weakness, numbness or other symptoms of nerve disorder, according to the Food Safety Authority of Ireland (FSAI).

Vitamin B12, which is subject to prescription control at doses over 25mcg, is for sale at 2,000mcg with a suggested dosage of up to 4,000mcg daily.

Dr Mary Flynn, chief specialist, public health nutrition of the FSAI, says the fact that some vitamins, such as B12, don't have a UL is not because no risk has been found but because there is insufficient evidence to set a UL. As a result, consumers need to exercise caution, given the RDA for this vitamin is just 2.4mcg daily for an adult.

Flynn says that products over the prescription level are automatically referred to the IMB. In addition, a risk assessment for the 100mg vitamin B6 would be carried out by the FSAI. The IMB says that its policy is to take action where claims are made or where there is a safety concern.

RDAs of vitamins and minerals for each section of the population are regularly reviewed as are the UL for each, according to Flynn. Upper limits are mostly developed for synthetic forms of vitamins and minerals (used in supplements and fortified foods) and less commonly apply to the natural forms found in food.

The UL refers to the maximum level which can be taken before adverse effects may be seen and will vary according to pregnancy, age and gender in healthy people.

Overdosing risks
The UL for vitamin A, for instance, includes food sources because of the risks posed by overdosing. High intakes of vitamin A can lead to birth defects.

Richelle Flanagan, president of the Irish Nutrition and Dietetic Institute (INDI), says she recently advised a pregnant woman to stop taking a multi-vitamin product which had been bought outside the country and which had vitamin A well in excess of the RDA. High doses of folic acid can interfere with chemotherapy, she adds.

The INDI would advise consumers not to exceed the RDA. She points out that someone taking fortified foods plus supplements may end up taking more than the RDA and urged consumers to look at their diet first and consult their GP or see a dietician before considering supplements.

Flynn says that one of the trials of beta-carotene in protecting smokers from cancer and heart disease during the mid-1990s had to be stopped early when it was found that the beta-carotene supplement put them at greater risk of death than those assigned a placebo or no supplement.

She pointed out that the way the body utilises vitamins in food is quite different to the way it absorbs synthetic vitamin supplements. Consumers aren't in danger of overdosing on beta-carotene in carrots but "this could easily occur when using beta-carotene supplements because supplements are concentrated amounts of a highly active synthetic form of the nutrient". Flynn adds that manufacturers and retailers should have regard to the effect of products both cumulatively and on future generations.
Consumers can find more information about the adverse effects of high doses of vitamins and minerals on the FSAI's website at fsai.ie/faq/food_supplements.