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Drug and vitamin interactions

MagazineAugust 2003 (Vol. 14 Issue 5)Drug and vitamin interactions

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

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).

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