The recent attack by UK health authorities on vitamin and mineral supplements was astonishing largely because of the flimsiness of the evidence of so-called dangers. But there may be a hidden agenda. One little known fact (except by pharmaceutical-industry leaders) is that taking nutritional supplements can affect drugs, often strongly, by cutting effectiveness in half, magnifying side-effects or radically altering its action. Vitamins can even reduce drug uptake.

Virtually every drug interacts with some vitamin supplement. Although GPs know that certain drugs interact with certain foods - for example, MAO inhibitors with cheese - it’s nearly impossible to keep track of which drugs are affected by which vitamins. A sample of some common ones from just A to C provides some idea of the scale of the problem.

* Acetaminophen (paracetamol) with vitamin C (J Pharm Sci, 1976; 65: 121-2) and N-acetylcysteine (NAC) (Lancet, 1995; 364: 547-52)

* Angiotensin-converting enzyme (ACE) inhibitors with potassium (JAMA, 1995; 274: 538) and zinc (J Am Coll Nutr, 1998; 17: 75-80)

* Alendronic acid with calcium, if taken at the same time, and possibly magnesium (Threlkeld DS, ed, Facts and Comparisons: Drug Information, St Louis, MO: Facts and Comparisions, 1998: 134)

* Aluminium hydroxide (antacids) with calcium, phosphorus and citrates (for example, calcium citrate) (Nutr Healing, 1997; 4: 4, 11)

* Amoxycillin with bromelain (Drugs Exp Clin Res, 1978; 4: 39-44)

* Antibiotics deplete the normal intestinal bacteria that produce vitamin K, which is important for proper blood-clotting

* Anticonvulsants with biotin (Neurology, 1997; 49: 1444-7), carnitine (J Korean Med Soc, 1997; 12: 553-8), vitamin D (Rec Prog Med, 1998; 89: 529-33), vitamin K (Am J Obstet Gynaecol, 1993; 168: 923-8) and folate (Acta Neurol Scand, 1984; 69: 226-31)

* Aspirin with vitamin C [BMJ, 1975; I: 208), vitamin E (Ann Med, 1998; 30: 542-6), folic acid (Blood, 1971; 38: 405-16) and zinc (Scand J Rheumatol, 1982; 11: 63-4)

* Atorvastatin with vitamin A (Metabolism, 1995; 44: 398-403), niacin (Am J Cardiol, 1994; 73: 339-45) and coenzyme Q10 (Mol Aspects Med, 1997; 18 [Suppl]: S137-44)

* Benzodiazepines with melatonin (Sleep, 1993; 16: 744-7)

* Cimetidine with vitamin B12 (Scand J Gastroenterol, 1982; 17: 129-31), vitamin D (Nutr Rev, 1985; 43: 184-5), iron (Med Toxicol Adv Drug Exp, 1988; 3: 430-48) and magnesium (Scand J Gastroenterol, 1994; 206: 14-9)

* Colchicine with vitamin B12 (N Engl J Med, 1987; 317: 1290-1)

* Corticosteroids and glucocorticoids with vitamin A (Ann Surg, 1969; 170: 633-40), vitamin B6 (Ann Allergy, 1993; 70: 147-52), calcium and vitamin D (Lancet, 1978; ii: 1123-5), magnesium (Holt GA, Food and Drug Interactions, Chicago: Precept Press, 1998: 83), N-acetylcysteine (NAC) (Am J Respir Crit Care Med, 1997; 156: 1897-901), potassium and sodium (Thelkeld DS, ed, op cit, 1991: 128b), dehydroepiandrosterone (DHEA) (Aust NZ J Med, 1994; 24: 396-401) and melatonin [J Pineal Res, 1987; 5: 317-22)

* Cycloserine with calcium and magnesium (Holt GA, op cit, p 86), folic acid, vit-amin B6, vitamin B12 (Roe D, Campbell T, eds, Drugs and Nutrients: The Interactive Effect, NY: Marcel Dekker, 1984: 288-9, 505-23) and vitamin K (Holt GA, op cit, p 85)

* Cyclosporin with vitamin E (Pharmacotherapy, 1996; 16: 59-65), magnesium (Lancet, 1984; ii: 1116) and omega-3 fish oil (J Am Coll Cardiol, 1997; 29: 1324-31).

>From this perspective, it is clear why the drug companies are persuading the authorities to get rid of effective, high-dose supplements in favour of lower, largely ineffectual doses.

Harald Gaier
Harald Gaier has moved to The Diagnostic Clinic (tel: 020 7009 4650).