Posted on: November 14, 2016 at 1:00 pm
Last updated: September 26, 2017 at 8:09 pm

This amazing guest post was written by Dr. Sarah Brewer, a licensed Medical Doctor, a Registered Nutritionist, a Registered Nutritional Therapist! Check out her website here!

While vitamins and minerals are often mentioned in the same sentence, the two are very different. Vitamins are complex molecules synthesized within the cells of the plants and animals from which our food derives. In contrast, the minerals that are essential for human health are found in the Period Table you once studied during chemistry lessons.

Essential minerals are metallic and non-metallic elements that play a vital role in body metabolism. Most of your mineral stores (around 3 kg) are in your skeleton but, despite that great reserve, mineral deficiencies are generally more widespread than vitamin deficiencies.

This is because the vitamin content of food tends to be similar wherever it is produced, as vitamins are synthesized by the plant and animal cells themselves.

In contrast, the mineral content of foods depends on the soil in which it was grown or reared. Selenium, for example, was leached out of the soil throughout much of Europe during the last Ice Age. Exposure to acid rain and food processing also significantly reduce the mineral content of foods.

Why Do You Need Minerals?

Minerals have many different functions and may:

  • Act as antioxidants (eg selenium, manganese, zinc)
  • Have structural roles (eg calcium, magnesium, phosphate)
  • Allow cells to maintain electrical potentials (eg sodium, potassium, chloride)
  • Promote muscle contraction (eg calcium)
  • Speed the action of enzymes (eg copper, iron, magnesium, manganese, molybdenum, selenium, zinc)
  • Bind oxygen for transportation (eg iron)
  • Promote hormone function (eg chromium, iodine)

Some trace elements such as nickel, tin, and vanadium are also recognized as essential for normal growth in only tiny amounts, but their exact role is not entirely understood.

Which Minerals Are Toxic?

While deficiencies are common, all minerals are toxic in excess – often in amounts that are not that much greater than the intakes needed for optimum health.


It’s therefore, important not to exceed manufacturer’s recommended doses, not to mix and match supplements that contain minerals, and to keep your supplements out of the sight and reach of children – particularly since many are colorful and resemble sweets.

Excess sodium is one of the best-known minerals for causing toxicity, including raised blood pressure, vomiting, kidney damage, acid imbalances, and can prove lethal. Most of us already get too much sodium from dietary salt, and multivitamin and mineral supplements are formulated only to provide minimal amounts.

4 Minerals That May Lead To Problems

The following minerals are the ones most likely to lead to problems if you regularly take a multivitamin and mineral supplement above the recommended dose.

NB All figures given are for adults.

1. Iron

Iron is a metallic mineral needed for the production of the red blood pigment, hemoglobin, and the red muscle pigment, myoglobin, which carry oxygen. Iron is also required by liver detoxification enzymes and for white blood cells to fight infection.   

What’s the problem with too much?

Iron is highly reactive, which is why it starts to rust on exposure to moisture and oxygen. Similar oxidation reactions can occur in the body, although this effect is minimized by antioxidants which ‘bubble wrap’ iron to help protect your cells.

While the absorption of dietary iron is complex and usually carefully regulated, high intakes can cause intestinal distress, with nausea and vomiting. Diarrhea or constipation can also occur. Toxicity is especially problematic for young children and can prove fatal as their ability to limit iron absorption has not fully developed.

People with hemochromatosis are also at risk. Haemochromatosis is a condition in which iron is absorbed in an unregulated way. It occurs when sometimes inherits two copies of a ‘faulty’ gene so iron is absorbed whether you need it or not.

There is no particular mechanism for the body to excrete excess iron, so excess quickly builds up in the liver and other organs and can lead to cirrhosis, hair loss, diabetes and heart failure. In the skin, excess iron can cause a noticeable bronzing which is how the condition is sometimes diagnosed.

Haemochromatosis affects around 1 in 250 people. As many as one in 1 in 7 of also have one copy of the faulty gene or other genetic variants that result in mildly increased iron stores. Although this rarely leads to significant iron loading, it may increase the risk of heart disease associated with raised iron levels.

What’s a safe intake for iron?

The US Daily Value (DV) for iron is 18mg, while the EU Nutrient Reference Value (NRV) is 14 mg for adults. The safe upper level for long-term use from supplements is suggested as 17mg per day (except under medical supervision to treat a confirmed iron deficiency). Diet should always come first, and good sources of iron are covered at this link.

Despite the prevalence of iron overload genes, iron deficiency is the most common nutritional disease, worldwide, with most cases going unrecognized. If you are advised to take an iron supplement by your doctor, you will usually have your blood count monitored so the iron can be stopped when necessary.

2. Magnesium

Magnesium is a metallic mineral needed for most body enzymes to work properly and is vital for maintaining the electrical charge across all cell membranes.

What’s the problem with too much?

Magnesium intakes that are only marginally above recommended intakes have a laxative effect. This is not always a bad thing, of course, and magnesium in the form of Epsom salts remains a popular remedy for constipation. Very high doses of magnesium salts are even used medically to clear the bowel before procedures such as colonoscopy and surgery.

Some people are more sensitive to the laxative effects of magnesium than others. A good way around this if you need magnesium supplements (eg to boost energy levels, reduce migraine attacks, or overcome restless legs) is to absorb it across the skin via a magnesium oil or bath salts.   


What is a safe intake for magnesium?

The US DV for magnesium is 400 mg, while the EU NRV is 375 mg per day. The upper safe limit for long-term use from supplements is suggested as 400mg per day. If taking magnesium supplements, it is important to ensure a proper intake of calcium to avoid imbalances.

3. Selenium

Selenium is a metallic trace element that is so essential for health that its incorporation into proteins (as selenocysteine, the 21st amino acid) is directly controlled by your genes. Selenium is present in at least 30 enzymes that are essential for cell growth, antioxidant protection, antibody synthesis and to protect against viral infections and cancer.

What’s the problem with too much?

Toxicity can occur with selenium intakes above 400 mcg, and intakes that are regularly above 800mcg daily can prove lethal. Symptoms associated with selenium toxicity include a garlic odor on the breath, salivation and a metallic taste in the mouth, dizziness, nausea, vomiting, fragile or black fingernails and hair loss.

What is a safe intake of selenium?

The US DV for selenium is 70 mcg per day, while the EU NRV is 55mcg. The tolerable upper intake level is suggested as 300 mcg per day from all sources, including food and supplements. If you eat a lot of Brazil nuts, you may approach potentially harmful intake levels very quickly.

A single Brazil nut can provide between 50mcg and 300mcg selenium depending on its size and the selenium content of the soil in which it grew! Some people recommend limiting your intake to no more than 4 Brazil nuts per day.

4. Zinc


Zinc is a metallic element needed by enzymes that regulate hormone responses, growth, sexual maturity, immunity, and wound healing. 

What’s the problem with too much?

Excess zinc causes abdominal pain, nausea, vomiting, lethargy, dizziness and can lead to anemia. Zinc affects iron and copper uptake and higher dose supplements usually provide zinc and copper in a ratio of 10:1 (eg 10mg zinc and 1mg copper).

What is a safe intake for Zinc?

The US DV for zinc is 15mg, while the EU NRV is 10mg. The suggested upper safe level for long-term use from supplements is 25mg. As always, the diet should come first, and high-dose zinc supplements are not usually needed.

Do You Need A MultiVitamin and Mineral Supplement?

I hope that hasn’t scared you off from taking a multivitamin and mineral as a nutritional safety net when you know your diet is not as good as it should be – for example, if you are cutting back to lose weight, or avoiding certain foods due to intolerances. 

Click here to download my free eGuide to help you decide if you need a multivitamin and mineral supplement, and where to obtain micronutrients from your food.

Click here to read my Expert Health Review of the best multivitamin brands.

Dr. Sarah Brewer
Dr. Sarah Brewer, MSc (Nutr Med), MA (Cantab), MB, BChir, RNutr, MBANT, CNHC, FRSM, is a medical nutritionist, nutritional therapist and the author of over 60 popular health books.

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