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Nutrition News Number 89/90

Updated 24/7/99


The Pros & Cons of 


"As a general rule, we should obtain our essential nutrients naturally, from foods. This should be a guiding principle"

Nothing beats a balanced, varied diet. Heavy and/or unbalanced supplementation can pose serious (even life-threatening) dangers. Supplements taken in large quantities fall into the category of a drug. Like all drugs, they may have side effects. In fact, they may have a completely opposite effect to the one Vitaminsintended. Recent research suggests that heavy supplementation may increase the risk of cancer. Vitamins A, C and E are strong antioxidants, but when used in excess, in unnatural quantities, they do a complete 'about-face' and turn into pro-oxidants. In this form, they are damaging to our health. By contrast, a balanced, varied diet provides the quantities our bodies need - naturally. Nevertheless, I believe it's a good idea for everyone to have a single mineral-vitamin capsule daily. If your diet is less than perfect (like most Western diets), it replaces missing nutrients - but in a harm-free manner, because (importantly) it usually contains only small doses of each constituent. Variations exist, however. Seek professional advice on the appropriate choice.

Who Needs Supplements ?

Certain groups and individuals may require supplementation.

Children: Anaemia due to iron deficiency is common in children. Unfortunately, once a child (or adult) becomes anaemic, high-iron foods (e.g. meat and liver) are insufficient to correct the complaint, and iron supplementation will be necessary.
Other supplements for children may include Vitamin K, mostly given to newborn babies to prevent bleeding tendencies. Vitamin B12 is given to babies of vegan mothers, because plant foods have no Vitamin B12, and the foetus may thus be at risk of pernicious anaemia.

Young women: At this time of life it is important to have sufficient calcium in the diet to build strong bones for the future, and hopefully to prevent osteoporosis in later life. After the age of 31 (approx.) calcium ceases to be laid down in the bones. Although found in diverse foods such as nuts, green leafy vegetables and small-boned fish, calcium is mainly sourced in dairy products. When the diet is deficient, a calcium supplement should be taken.

Menstruating and Child-bearing Women: This group is often iron-deficient due to frequent and/or heavy periods, and requires iron supplementation.
Folate (folic acid) supplements should be taken if pregnancy is a possibility - even before conception. This will reduce by 50% to 75% the risk of neural tube defects (e.g. spina bifida) in the baby. Folate deficiency can also cause anaemia - a different type from iron deficiency anaemia - in the mother.
Iron and folate tablets are often given routinely to pregnant women.

Lactating Women: A calcium supplement may be necessary to replace the calcium the mother is losing in her breast milk.

The Elderly (over 65): Elderly people who are institutionalised may need a Vitamin D supplement if they do not receive sufficient exposure to the sun.
The diets of the elderly are often zinc-deficient. Zinc supplements (e.g. 50 mg daily) are then indicated, to help sustain immunity. This may prevent pneumonia and may also reduce macular degeneration, a common and incurable cause of blindness.
Elderly people often have difficulty absorbing certain nutrients in their diet - due, for example, to lack of stomach acid. In this case a B12 supplement, in a simple daily multi-vitamin capsule (as mentioned before) is a good idea.

Osteoporosis sufferers may benefit from calcium supplementation and possibly also from Vitamin D and fluoride.

Some Effects of Vitamin Overdose

Vitamin A: A dose in excess of 3000 mg daily may be associated with birth defects, liver toxicity, bone and nerve damage, and hair loss.

Vitamin E: Trials have shown that supplementation may lower the risk of coronary heart disease, but may slightly increase the risk of haemorrhagic stroke. The suggested dose is 400 I.U. per day. Unfortunately, scientists are as yet uncertain if this is the correct dosage. Vitamin E may also improve athletic performance and give protection against cataract formation, and help diabetes sufferers. But excessive dosage - over 1000 mg per day - may cause iron overload in men, gastroenteritis, pernicious anaemia (by interfering with B12 absorption), and unhealthy levels of copper. It may also lead to kidney stones and can cause nausea, diarrhoea, and harm to a foetus if taken by the mother during pregnancy.
Vitamins A and E, taken together, may be harmful to the immune system.

Beta carotene, an antioxidant and precursor of Vitamin A, has been shown to increase lung cancer in smokers when given in megadoses.

Vitamin B3 (niacin) is sometimes used in large doses to to reduce high blood cholesterol and blood fats (triglycerides). But in doses exceeding 500 mg daily, it may cause liver toxicity and gastrointestinal reactions, and may also cause flushing, and excess blood uric acid (the cause of gout).

Vitamin B6 may sometimes benefit women with morning sickness, pre-menstrual tension or mammary dysplasia. However, more than 200 mg per day may lead to sensory neuropathy.

Folic acid (folate) may lower the level of serum homocysteine, a chemical in the blood which, when present at high levels, may account for 10% of heart attacks. Folate supplementation is also recommended before and during pregnancy (as described earlier). The suggested safe level of supplementation is 0.4 mg per day. More than 5 mg per day may mask anaemia caused by Vitamin B12 deficiency, and interfere with zinc bioavailability. Thus it is often wise to accompany folate supplementation with B12 supplementation.

Vitamin C (ascorbic acid) may shorten the duration of colds and may help prevent stomach cancer by stopping the synthesis of nitrosamines (which are carcinogenic). But an excess of Vitamin C can cause diarrhoea, kidney stones, reflux, dental erosions and gastrointestinal obstruction.

Vitamin D in excess can cause hypercalcaemia and birth defects.

Some Effects of Mineral Overdose

Iron: Excessive intake can lead to iron overload in susceptible subjects. Iron may be deposited in the heart, pancreas and liver, leading to disease in these organs. Iron excess can also interfere with zinc absorption.

Zinc: In excess, zinc may decrease immunity and inhibit the absorption of copper, an essential mineral.

Selenium: This is a component of a powerful antioxidant found in the body. But an excess can turn it into a harmful pro-oxidant, which decreases immune function. A trial using 200 micrograms daily (incorporated in yeast) showed a decrease in lung cancer mortality and in colorectal and prostate cancers. On the other hand, more than 600 micrograms per day may cause nail, skin, teeth and nerve toxicity.

Magnesium: Chocaholics are said to benefit from a magnesium supplement. The reasoning is that, because chocolate is rich in magnesium, taking the supplement may quell the craving! A recent trial suggests that daily magnesium supplements may help lower blood pressure. Butů
Calcium and Magnesium supplements, in large doses, can interfere with the absorption (and therefore the efficacy) of tetracycline antibiotics. They should be taken at least three hours apart. Calcium supplements are recommended for anyone, in any age group, whose diet is deficient in dairy products. They are also advised for many osteoporosis sufferers.

Chromium: Improves HDL ("good" cholesterol) and lowers LDL ("bad" cholesterol) in those suffering from non-insulin dependent diabetes. It has no effect on total cholesterol. Chromium supplementation may also benefit the elderly, whose diets are often lacking.

Effects of Herbal Supplements on Prescription Drugs

Herbal medicines and supplements are highly popular. The problem is that most of them remain scientifically untested, many imported varieties are contaminated (with heavy metals, pesticides, antibiotics, for example), and composition may vary wildly from one source to the next. These supplements may also interact with prescribed medications, sometimes with fatal results. For example:

*Echinacea may interact with hepatoxic drugs to cause liver damage if used for more than eight weeks. With immunosuppressants, it becomes an immunostimulant.

Evening Primrose Oil or Borage taken with anticonvulsants may lower the sufferer's seizure threshold.

Feverfew and NSAIDS taken together may offset the herb's effect for migraine. Feverfew taken with Warfarin may alter bleeding time.

Ginseng taken with oestrogen or corticosteroids my have possible additive effects; with phenelzine may cause headache, manic episodes or tremulousness; with warfarin may alter bleeding time; with digoxin interferes with the drug and/or monitoring. Ginseng and karela should be avoided by diabetes sufferers as they may affect blood glucose levels.

Kava taken with alprazolam has led to coma.

Kelp is a herbal source of iodine and may interfere with thyroid replacement therapies.
Licorice used with spironolactone or digoxin offsets the drug's effect and interferes with the drug and/or monitoring.

St. John's Wort taken with MAO inhibitors or SSRIs (anti-depressants) is ill-advised, as the herbal mechanism of action is unknown.

Valerian taken with barbiturates may result in excessive sedation

In addition to the above, hawthorn, kyushin, licorice, plantain and uzara root all interfere with the function of digoxin and digoxin monitoring.*

*Source, Dr L. Millar, Archives of Internal Medicine (1998: 158, 2200-211)

In summary, vitamin and mineral supplements can prove valuable in certain instances. But great care must be taken with regard to dosage. Overdosing may lead to a negative effect. Supplements may also clash with existing medication - even with each other. Conversely, certain drugs may cause mineral and vitamin deficiencies, and interfere with he absorption of nutrients and / or other drugs. In this case, supplementation may be required. Be sure to seek your doctor's advice. We all have different needs, and your doctor will be able to advise you of the best course in your own particular case. If you are healthy, and your diet is balanced, heavy supplementation may be not only a waste of money but a distinct risk to your well-being.

For more about Supplements, read Dr Clive Barnett's new book, "Doctor in the Kitchen : a Feast of Protective Foods" - packed with invaluable advice on nutrition, and featuring over 50 fabulous recipes. Available at

Copyright © 1998 Clive Barnett



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