Vitamin Poisoning

Are you taking too many vitamins? Do you know the harmful effects of consuming excessive vitamin and mineral supplements?

Vitamin deficiency syndromes are uncommon in Western countries. Overeating is more prevalent than starvation.

Then why 30 per cent of the population consumes over-the-counter vitamin and mineral supplements?

The answer is simple. They hope to improve their health and prevent disease. For healthy individuals, experts recommend the following vitamin supplements:

1. folic acid (400 ug/day) – reduces the risk of heart disease, colon and breast cancer and birth defects during pregnancy,
2. vitamin B6 (2 mg/day) – keeps homocystein levels down and reduces the risk of heart disease,
3. vitamin B12 (6 ug/day), – same as B6 plus reduces the risk of cancer,
4. vitamin D (400 IU/day) – minimizes risk of osteoporosis and fractures,
5. omega-3 fatty acids (1000 mg/day or eat fish two to three times a week) – reduces the risk of sudden heart attack by 50 to 80 per cent, and
6. a multivitamin will ensure an adequate intake of other vitamins for which the evidence of benefit is indirect.

Regular use of vitamin E and C remains controversial.

Recently, the UK Food Standards Agency reviewed 36 vitamins and minerals and discussed the potential harms that can come from consuming such supplements. This information is summarized in the Canadian Medical Association Journal by Dr. Eric Wooltorton.

If a person consumes high doses of some vitamins, especially taking them on a regular basis, may suffer from side effects. The side effects generally involve the liver, stomach and bowel. Such as: nausea, vomiting, diarrhea, liver damage, visual problems, nerve damage etc.

The CMAJ article says that minerals taken as supplements can also be toxic. For example:
-magnesium can cause diarrhea at doses above 400 mg/d;
-phosphorus can cause diarrhea at doses above 750 mg/d, and mild nausea and vomiting at lower doses;
-iron can cause constipation, nausea and vomiting, reduced zinc uptake, and iron overload;
-zinc can cause nausea and vomiting, immunosuppression and impaired copper uptake; and
-selenium at doses above 0.91 mg/d can cause brittle hair and nails, peripheral neuropathies and gastrointestinal upset.

Is it possible to prevent vitamin and mineral toxicity?

Yes, regular screening enquiries about the use and dose of vitamin and mineral supplements may help to optimize a patient’s nutrient intake and avoid potential harm from inappropriate use of supplements (e.g., intake of beta carotene by smokers may increase the risk of lung cancer), says CMAJ article.

The article says that the European Union recently moved to adopt strict labeling standards for vitamin and mineral supplements, including having manufacturers list the percentage of a person’s daily intake that is represented by one dose of the product, as well as toxicity warnings when they are appropriate.

Will Canada adopt similar standards? asks Dr. Wooltorton. Only time will tell. In the mean time, do not over dose yourself with vitamins and minerals. Eat a healthy diet, eat lots of fruits and vegetables, exercise regularly and take vitamins as described above.

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Vitamin B12

Dear Dr. B: Thank you for your columns on Vitamin C and other vitamins. What about vitamin B12? Many people are on B12 injections on regular basis. Why is B12 important? Yours, Ms. B12.

Dear Ms. B12: Vitamin B12 deficiency is a common problem that affects the general population and the elderly in particular. Persons with the deficiency may have no symptoms or may have symptoms related to blood disorder or disorders of the nervous system including psychiatric problems.

Vitamin B12, also known as cobalamin, was first isolated in 1948 and was immediately shown to be effective in the treatment of pernicious anaemia. Recently, interest in the vitamin has been renewed because of the recognition that B12 deficiency occurs in 3% to 40% of the general population.

Vitamin B12 is essential for good health. It is obtained primarily from animal proteins (i.e., red meat, poultry, fish, eggs, and dairy). But the vegetarians can get enough of it from legumes. The cause of B12 deficiency is not usually poor diet but problems with absorption in the gastro-intestinal tract.

Absorption of vitamin B12 from foods is complex; a defect in any step can lead to deficiency. In the stomach, gastric acid and pepsin is required for digestion of B12. In the upper small intestine, pancreatic enzymes and an alkaline pH is necessary. B12 is absorbed from the terminal ileum (last part of the small intestine where it joins the colon).

The liver contains most of the body’s B12 (about 1.5 mg), followed by the kidneys, heart, spleen, and brain. Normal body stores of vitamin B12 range from 2 to 10 mg; daily losses are 2 to 5 micrograms. The stored B12 can last us two years in conditions where our body is deprived of B12.The latest Recommended Dietary Allowance (RDA) for vitamin B12 is 2.4 micrograms/day for persons aged 14 to 70 years; the average diet contains about 5 micrograms daily.

The diagnoses of B12 deficiency is made by checking the blood levels in patients who have symptoms or who are prone to B12 deficiency. Treatment is by B12 injections on regular basis for the rest of person’s life.


A reader wants to know the following:

What is the difference between micrograms (ugm.), milligrams (mg.) and International Units (IU)?

1000 micrograms is 1 milligram.

International unit (IU):
Is a unit used to measure the activity (that is, the effect) of many vitamins and drugs. For each substance to which this unit applies, there is an international agreement specifying the biological effect expected with a dose of 1 IU. Other quantities of the substance are then expressed as multiples of this standard. Examples: 1 IU represents 45.5 micrograms of a standard preparation of insulin or 0.6 microgram of a standard preparation of penicillin. Consumers most often see IU’s on the labels of vitamin packages: in standard preparations the equivalent of 1 IU is 0.3 microgram (0.0003 mg) for vitamin A, 50 micrograms (0.05 mg) for vitamin C, 25 nanograms (0.000 025 mg) for vitamin D, and 2/3 milligram for vitamin E. Please note: for many substances there is no definite conversion between international units and mass units (such as milligrams). This is because preparations of those substances vary in activity, so that the effect per milligram of one preparation is different from that of another.

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Essential Vitamins

More people consume vitamin supplements now than ever before. Do we know what is the right vitamin to take and how much of it do we need?

This issue is discussed in a Clinical Practice article in the New England Journal of Medicine (NEJM) titled, “What vitamins should I be taking, doctor?”

Medical teaching says that a healthy individual, who eats a good diet, does not require vitamin supplements. He should be able to meet his vitamin needs from his healthy diet. But the public interest in vitamin supplements is enormous – sometimes due to misguided reasons. Almost 30 percent of our population takes vitamin supplements. And there is no control over it.

Because the food we eat contains too many nutrients, it would be almost impossible to conduct double blind trials to see if vitamins do have improved clinical outcomes. Also the users of vitamin supplements may have healthier lifestyles or behaviours than nonusers. This would distort any clinical trial results.

The good thing about vitamin supplements is that there is greater likelihood of good than harm and cost of supplements is not that high so the authors of the article in the NEJM recommend the following vitamin supplements for healthy individuals. There is substantial evidence that higher intake of:

1. folic acid (400 ug/day),
2. vitamin B6 (2 mg/day),
3. vitamin B12 (6 ug/day), and
4. vitamin D (400 IU/day) will benefit many people, and a
5. a multivitamin will ensure an adequate intake of other vitamins for which the evidence of benefit is indirect.

The authors say a multivitamin is especially important:

-for women who might become pregnant
-for persons who regularly consume one or two alcoholic drinks per day
-for the elderly, who tend to absorb vitamin B12 poorly and are often deficient in vitamin D
-for vegetarians, who require supplemental vitamin B12 and
-for poor urban residents, who may be unable to afford adequate intakes of fruits and vegetables.

Physicians who encourage their patients to take vitamin supplements should also educate their patients regarding healthy life style and about healthy nutritious diet. Foods contain many additional important components, such as fiber and essential fatty acids and vitamin pills cannot be a substitute. Vitamin pills do not compensate for the massive risks associated with smoking, obesity, or inactivity, say the authors of the NEJM.

What about vitamin E?

The authors feel that vitamin E supplements are reasonable for most middle-aged and older individuals who are at increased risk for coronary artery disease. Although the final verdict on its benefit in prevention of heart disease is not in, the authors feel that it is reasonable to take 400 IU of vitamin E daily. But this should be reviewed annually as more information becomes available.

The authors do not recommend any additional vitamin supplements at present, as the evidence required to make such recommendation is far from complete.

The message here is pretty clear. First practice healthy lifestyle: regular exercise, healthy diet (high fibre, low fat diet with lots of fruits and vegetables), no smoking, weight control, and stress management (remember ELMOSS?). Then spend money on vitamin supplements.

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Vitamin C

In the 16th century, the Dutch sailors knew that eating citrus fruits prevented scurvy. But it wasn’t until 1920s when it was recognised that the active ingredient in citrus fruits was vitamin C (ascorbic acid).

The next big development for vitamin C came in 1974. A research paper was published with careful description of the responses of 50 consecutive patients with advanced, untreatable cancer to high-dose intravenous and oral vitamin C.

Most patients in this group of 50 did not respond to high doses of vitamin C. But extraordinary things happened to a significant minority of them. These included several cases of tumour regressions.

This report generated some controversy. In 1991, a panel set by the US National Cancer Institute, reviewed 25 of the 50 patients who had complete remission of the tumour. The panel found that in each and every case, “there were alternative explanations for the observed remissions”.

So, what do we know about vitamin C and its usefulness in cancer prevention and treatment?

Vitamin C is known to play an important role in the synthesis of collagen (fibrous protein of connective tissue), to promote wound healing and to influence many immunological and biochemical reactions in the body.

In laboratory animals, vitamin C has been shown to have a range of effects that could be beneficial to cancer patients, including tumour regression, the inhibition of tumour growth and increased survival on animals with implanted cancer.

There is some evidence that populations whose dietary intake of vitamin C is high have a decreased risk of some types of cancer, cardiovascular disease and cataracts. Vitamin C supplements are generally well tolerated. In adults, a dose of one gram per day is safe with minimal toxicity. Very minimal toxic effects have been reported even at much higher doses.

Vitamin C can interfere with absorption of many other medications: blood thinners, iron, vitamin B12, and vitamin E.

Humans cannot manufacture vitamin C. We have to obtain it from dietary sources. It is found in many fruits such as oranges, grapefruit, strawberries, raspberries and kiwi fruit, and in vegetables such as cabbage, tomatoes and bell peppers.

Canada’s Food Guide, prepared by Health Canada, sets guidelines for the recommended daily intake (RDI) of vitamins and minerals. Most people who eat a balanced diet that is made up of a variety of foods and that is rich in fresh fruits and vegetables will meet the RDI of vitamins and minerals.

Advocates of mega dose vitamins often recommend combining vitamins A, C, and E and claim that these vitamins improve general well being, strengthen the immune system and may delay the development and progression of serious disease.

Is this information good enough to make a strong case for vitamins in the management of cancer patients?

In 1998, the Canadian Medical Association Journal (CMAJ) ran a series on “Unconventional therapies for cancer”. The article on Vitamin A, C and E says: There is some laboratory evidence and some clinical evidence that vitamins A, C and E, given separately or on combination, may have value in the management of cancer. However, there is a lack of solid scientific evidence of the sort required to support a recommendation that cancer patients take vitamin supplements.

In the last few years, rational guidelines fro testing biological agents like vitamin C have been developed, says the CMAJ. And hopefully new information on the benefits of vitamin C should be forthcoming. The good thing about vitamin supplements is that they are readily available, can usually be self-administered and are relatively inexpensive and non-toxic for most adults. And hopefully, there will be more good news in the years to come.

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