Updated 22 October 2013

Are you overdosing on supplements?

If you are taking supplements to counteract the harmful effects of drinking, smoking, stress and lack of sleep on your body, you could actually be harming your health, warns registered dietitian Karen Protheroe.

Most people generally love popping pills either regularly or when a scratchy throat warns of an impending cold.

These days our lives seem to be so full of stresses that one feels the need for extra supplementation to counteract all the abuse we put our bodies through from alcohol, smoking, lack of sleep and pollution.

Also we are either too lazy or too busy to consistently prepare healthy meals, rich in nutrients. Or we don’t trust that the food we buy is still high enough in nutrients (due to modern farming practices, leached soils and so on) so again one tends to pop pills that promise better fitness, energy levels as well as health.

But are we jumping from the frying pan (should be grilling not frying) into the fire?

Marketing strategy

Firstly, it is my belief, that it is the supplement companies who make the claims about our soils being leached and our food being nutritionally poor as it is an effective marketing strategy for selling supplements.

These days we know so much more about healthy farming practices than in the past, which have not only become much more scientific, but also controlled as far using pesticides and fertilisers as well as improving the soil by adding organic material, crop rotation etc.

Secondly, nutritional supplements in South Africa are not regulated or tested like our medicines and foods are tested by the Food and Drug Administration (FDA). So that means that supplement companies can put what they like in the supplements and say what they like in the marketing of such supplements.

A recent study of sports supplements found that approximately 30% of the randomly tested supplements had banned substances in them.


The Nutrition Information Centre of the University of Stellenbosch (Nicus) a while back released a public statement claiming that "Supplementation of antioxidants could increase the risk of death". A recent meta-analysis of data from 68 well conducted trials with 232 606 participants in Europe, the Americas, Asia and Australia including lower- and higher-income countries, indicate that antioxidant supplements, singly or in combination with other nutrients, given at different doses and duration increase all-cause mortality.

In other words, taking supposedly health promoting vitamins and minerals could cause you to die sooner from diseases, than if you were not taking anything. The guilty supplements were beta carotene, vitamin A and vitamin E. Vitamin C supplement was not found to be bad, but was shown to be ineffective in prolonging life.

Iron supplementation can not only cause constipation but can also lower your immune system and therefore make you at risk for developing infections.

High doses of zinc can cause the same effect as well as reducing ones good cholesterol and causing headaches.

High doses of omega-3 fatty acids or fish oils (very trendy at the moment) can cause low blood pressure as well as increasing your bleeding time – not ideal if planning to have an operation or accident in the near future.

I could continue to list known negative effects of taking high doses of various supplements but there are also many negative side effects we are only just discovering!

So should one take nutrient supplements?

The following recommendations were made by Nicus. If you think you need supplements, it would be more beneficial to consider the following:

  • Make sure you are consuming an adequate diet which includes a variety of foods  
  • Consult an expert on the adequacy of your diet  
  • Avoid supplements with glamorous multi-claims which cannot be substantiated when scrutinized  
  • Avoid single nutrient supplements  
  • Check the composition of the supplement you plan to take or you are taking  
  • Choose a multi-vitamin, multi-mineral supplement that has up to two times the recommended amount only
  • Reassess your need to take such supplements regularly and for prolonged periods  
  • Report to your doctor any adverse effects you think may be linked to the supplements

Just to add to this, some supplements can also interfere with the action of your prescription medication so always mention to your doctor what supplements you take.

Also look for supplements that are free from artificial preservatives, colourants and flavourants.

Supplements commonly taken by runners or those doing other intense training

Iron supplementation

Runners do generally have higher needs for iron so it is important to optimise and preserve ones iron stores.

To do this, you need to eat a diet high in animal protein especially darker meats such as red meat, organ meat and brown fish.

Iron from vegetable sources is poorly absorbed, which is why vegetarian runners will struggle to preserve their iron stores without supplementation (especially women who menstruate).

When eating a food that is rich in iron, eat or drink something that is high in vitamin C as vitamin C will increase and improve the absorption of iron from that food.

Good sources of vitamin C include: citrus, tomatoes, peppers, berries, potatoes (with skin), broccoli and cabbage.

Vegetarians, growing teenagers and pregnant women will most likely need to take iron supplements.

Before taking a supplement, it is better to ask your doctor to test your iron stores (ferritin levels). It is necessary to have a blood test for this rather than a finger prick hemoglobin test. 

Take your iron supplement in two separate doses separate to your meals in order to increase your absorption as fibre, tannin in tea and caffeine all reduce the absorption of iron.

If taking your supplement makes your feel nauseous then take it just before going to sleep at night. The average female needs 18mg of iron per day (from food or supplements) (pregnant woman need 30mg/day) and males need 8mg but runners may need an extra 30 – 70%. The upper limit of safety after which iron will become toxic is 45mg/day. 

Calcium and magnesium supplementation

A lot of runners take calcium and magnesium to help reduce or prevent cramping which is very common. Supplementation companies have effectively marketed many cal/mag supplements for this purpose.

However, scientific studies have not shown any benefit in taking these supplements and the main cause of cramping is not a deficiency of either of these minerals but is due to fatigue.

Taking ultra-high doses of magnesium could cause diarrhoea. Those runners avoiding dairy will need to take a calcium supplement unless they eat the soft bones found in pilchards and sardines as well as fortified milk alternatives and juices on a regular basis. Most people need approximately 1000mg of calcium per day. High doses of calcium could decrease the absorption of iron, magnesium and zinc.

So what should intense exercisers be taking?

Firstly and most importantly we should be "taking a healthy diet". Eat regular, varied meals that are cooked from scratch using a variety of fresh ingredients. Small changes to your food preparation can preserve the nutrient quality of those foods and prevent losing valuable nutrients.

All relevant studies have shown that diets rich in fruit and vegetables will preserve and optimise health.

Some vitamins are destroyed by heat and light so try to eat your veg and fruit in raw form as much as possible. Avoid soaking and cooking in water where possible, rather steam or grill or bake. When buying your veg and fruit make sure your get it home as quickly as possible and store it appropriately.

You should eat 2-3 (preferably different) fruits per day and 3-5 vegetable servings per day.

Secondly, intense exercisers could cover their bases by taking a general multivitamin. Those who may be at risk for developing a deficiency or who are experiencing symptoms of being deficient (such as fatigue, muscle weakness, shortness of breath and frequent infections) should see a sports doctor or dietitian rather than just swallowing a handful of pills.

Written by registered dietician, Karen Protheroe, of The Lean Aubergine Dietetic Services. To sign up for the monthly Lean Aubergine newsletter send an e-mail to or

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