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Here Are Some Tips on Safe Use of Dietary Supplements

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Many people take dietary supplements unaware of their hidden side effects, some of which are unpleasant or dangerous. Which are the risky or even hazardous supplements? 

Some people need to take supplements if, for instance, their body is deficient in, or cannot produce or process, what is needed in the usual ways.

Worldwide, people spend vast amounts of money on dietary supplements, around $160bn per year. Why? Presumably, because they believe the supplements will bring them benefits. Do they? Do supplements help or harm? Let’s explore some.

The human body can store some vitamins and not others. Fat-soluble vitamins (A, D, E and K) dissolve in fat and can be bodily stored. The water-soluble C and B complex vitamins cannot be stored and must be regularly topped up for good health.

Omega-3 fatty acids and folic acid seem to have a beneficial effect on heart health. Omega-3 can be found in fatty cold-water fish, nuts, and dairy products…

People without heart risk factors seemed not to benefit from taking Omega-3 supplements in a recent study. What would explain that?

Omega-3 and most other essential nutrients can be obtained from so many sources in a healthy diet that there is no need for supplements or dietary additions.

What the science says

Most of the evidence indicates that deductions from the diet are more effective than supplements to our eating habits.

Reducing the consumption of harmful sources is hugely beneficial for us. Refraining from smoking, drinking alcohol, overeating, eating fatty foods and avoiding immobility can bring us more benefits than all the supplements combined.

Some people take supplements thinking that they will somehow undo the consequences of their previous harmful consumption. There is no evidence that such compensatory use of supplements has any effect that could not be obtained from a healthy diet.

Regarding the scientific evaluation of supplements, few have been properly tested. Yet most manufacturers make claims that have no evidence base or make claims that amplify the most tenuous of evidence.

Some of the wording on supplement packaging and marketing is carefully crafted to avoid litigation: “may help with…” “is thought to be good for…”

In other words, litigation is avoided by indicating that any benefits of the product are based on the speculation of an untested hypothesis.

Alas, many members of the public do not have enough knowledge of science, or misleading word-craft, to know that they are being sold on speculation, not on fact.

If a healthy person has a diet which naturally contains their needed spread of nutrition, there is no need for any supplements. There is no added benefit when we go beyond 100% of our daily needs for vitamins and minerals.

The opposite may be the case: in many instances going beyond 100% of our daily needs can harm us. Vitamin D, made in the body after exposure to sunlight, helps the body absorb and regulate calcium and seems involved in regulating phosphorous levels, too.

Too much vitamin D causes excess calcium (hypercalcemia) to settle in the arteries (harmful) and not in the bones. Too much calcium has also been linked to an increased risk of cancer.

As with many aspects of life, too much Vitamin D can be as harmful as too little. Too much causes nausea, weakness and fatigue, and in extremis, kidney damage. Too little can trigger similar symptoms for different reasons.

Some people will take supplements to ensure against any shortfall in vitamins and minerals in their diet. Alas, there is no conclusive evidence that doing so helps. What would be wiser is to ensure that our diet is healthy and there are no daily shortfalls.

Other people go beyond attempting to insure and use multivitamins and multi-minerals as compensation for a poor diet. Recent evidence that multi-processed foods are involved in ill health may have implications. Many multivitamins and multi-minerals are heavily processed and may be causing the very illnesses they are claimed to prevent because they are so processed.

Dangerous and unknown interactions

When potentially therapeutic drugs are safety evaluated, they are not tested on all the possible permutations of excess levels of vitamins and minerals in the body; there are too many combinations to test.

What does that mean? That it can be dangerous to take supplements when on medication. For example, vitamin D, we know from adverse reactions, interacts with some weight loss medications, some statins, corticosteroids, diuretics…

Where adverse reactions have uncovered those dangerous interactions, your physician should alert you to the risks. Your physician cannot alert you if interactions are unknown or have not yet been detected.

Do you want to take supplements when you know that many (most?) have not been tested for interactions with many (most?) medications?

St John’s wort is a plant claimed to be beneficial for all sorts of ailments. Some of those claims seem to be accurate. However, and it is a big however, St John’s wort is known to have dangerous interactions with several medications.

Indeed, a study found that about 28% of the times it was prescribed, it was in dangerous combinations with other medications.

St John’s wort is known to interact with warfarin, chemotherapy, birth control pills, HIV medication, and antidepressants.

Several other vitamins and minerals, essential for good health, can cause ill health when too much is ingested.

Things you should know when using dietary supplements

  • Too much vitamin A can cause nausea and/or vomiting, dizziness, and blurred eyesight.
  • Excess vitamins in the B cluster {B1 (thiamine), B2 (riboflavin), B3 (niacin), B5 (pantothenic acid), B6, B7 (biotin), B12…} are known to cause tingling and numbness in bodily extremities, digestive problems, skin rashes, insomnia, severe mood swings, and blood pressure problems.
  • A vitamin C overload can lead to nausea, abdominal cramps, diarrhoea, vomiting, heartburn, and headaches. One early indicator of vitamin C overdose is orange urine.
  • Superfluous vitamin E can result in risks such as bleeding, including bleeding in the brain (hemorrhagic stroke), and similar known symptoms for vitamin C overdose.
  • Calcium excess can interfere with our kidneys, increase the pH of our blood, and lead to nausea and vomiting, confusion, itching, and an irregular heartbeat
  • Too much potassium (hyperkalemia) can cause fatigue and weakness, paralysis, cardiac arrhythmias…
  • A surfeit of sodium leads to thirst, fatigue, dry mouth, restlessness, increased heart rate, muscle spasms, seizures, coma, brain damage, or death (in extreme cases).
  • Masticating too much magnesium has seen symptoms such as nausea, diarrhoea, low blood pressure, muscle weakness, fatigue, and death.
  • Ingesting iron in immoderation can lead to nausea, vomiting, stomach pain, organ failure, internal bleeding, coma, seizure, and death.
  • A superfluity of selenium can cause nausea, vomiting, nail discolouration, brittleness/loss, hair loss, fatigue, irritability and halitosis.

Many others, taken in excess, can cause illness, such as zinc, iodine, chromium, copper, fluoride, molybdenum, manganese…

Many cases of vitamin or mineral overdose come from people taking supplements. Each year there are large numbers of hospitalisations due to supplement overdose.

Let’s not pretend that anyone understands the complex interaction of all the chemicals in the body. We understand the effects of the extremes of the major vitamins and minerals. How they interact is, at best, partially understood.


For most of us, our bodies find a natural, healthy balance, which remains, unless we do something to disturb that balance. Taking too much of any one vitamin or mineral can disturb our internal balance and cause many problems.

What happens if we take too much of (vitamin or mineral) one, four and nine and too little of two, three, six, seven, and eight?

We don’t know how each profile of overdose interacts with each person’s unique body any more than we know why in some people, our immune system starts attacking the myelin sheaths on our nerve fibres to cause the disease we call MS, multiple sclerosis. We know very little about body chemistry.

If you are healthy and eat a healthy diet, it seems to me that the unknown risks of taking untested supplements outweigh any unproven and uncertain benefits they may or may not provide.

For most people with no medical reason to take supplements, it seems that eating a healthy diet is cheaper and safer.

Professor Nigel MacLennan runs the performance coaching practice PsyPerform.


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