Drug Interactions

What is it?

From the occasional glass of wine to powerful medications used to fight cancer, drugs have the ability to affect nutritional status and health in a variety of ways. There are more than 100 000 medications available in America and almost two billion prescription drugs are dispensed every year. Many of these drugs affect the way the body uses vitamins and minerals from food. In most cases, medications deplete nutrients gradually and deficiencies may not be noticed until stores are exhausted. Alcohol also affects nutrient status and while light drinking may have some beneficial effects, heavy use carries a high risk of malnutrition. It is important to understand how drugs affect the body in order to minimize adverse effects, enhance recovery and maintain optimal health.

Drug-induced nutrient deficiencies

In most cases, unless drugs are used on a long-term basis, the effects on individual nutrients are not long lasting. Vitamin and mineral deficiencies are more likely to occur in people who take medications for long periods, particularly if their diets are usually low in essential nutrients. This type of medication use typically occurs in those with gastrointestinal disorders, diabetes, cancer, epilepsy, cardiovascular disease and autoimmune diseases. Alcohol, tobacco and oral contraceptives also fall into this category.

Elderly people tend to take more prescription and non prescription medications than any other group and usually also have increased needs, reduced appetite and absorption. This combination means that they are at high risk of drug-induced deficiencies. Children, pregnant women, those on reduced calorie diets and alcoholics are also susceptible.

Prescription and nonprescription drugs can interact with nutrients in a number of ways.

Alterations in appetite

Many medications can increase or decrease appetite, which can lead to a change in the amounts and types of food a person eats. Some drugs, such as some antihistamines and antidepressants can increase appetite. In some cases this may be desirable, but in others there may be an increased risk of obesity and the complications this causes. Many medications reduce appetite. Some are intended to do so, such as amphetamines for weight loss, and others do so as a side effect. If weight loss occurs in those who are already underweight, malnutrition may occur.

Some drugs affect the gastrointestinal system, causing nausea, vomiting, constipation or diarrhea. Others alter the production of saliva and the ability to taste, reducing a person's ability to enjoy food. Some drugs affect mood and alter the desire to eat. Drugs with these effects contribute to reduced intake and can lead to vitamin and mineral deficiencies.

Alterations in absorption

Some medications alter the absorption of vitamins and minerals so that even if dietary intake is sufficient, the body may not absorb enough for optimum health. Other medications bind vitamins and minerals in the intestine and reduce the ability of the body to absorb them; for example mineral oil laxatives reduce absorption of the fat soluble vitamins A, D, E and K.

Other drugs reduce the amount of time food spends in the intestine which means that the body may not have time to absorb all it needs. Others may block absorption sites or alter them so vitamins and minerals cannot pass through. Some drugs may affect absorption by changing the acidity of the stomach and intestines. In some cases the production of digestive juices essential for breakdown and absorption may be reduced.

Alterations in metabolism

Certain drugs alter the availability, storage and use of nutrients. Some of these chemically resemble vitamins and minerals and can bind to the same active sites on an enzyme. However, these drugs may not have the same beneficial effects as a vitamin and this can lead to deficiency symptoms. Other drugs may alter storage.

Some medications increase excretion of certain nutrients. This means that a particular vitamin or mineral is not retained in the body long enough to have beneficial effects; for example, some diuretic drugs increase potassium excretion.

Alcohol

Heavy alcohol use can lead to nutrient deficiencies. Many of the nutritional problems of heavy drinkers occur because of the direct effects of alcohol, but deficiencies are also partly due to the tendency of alcoholics to replace food with alcohol. Heavy alcohol use reduces vitamin and mineral absorption, damages the intestinal lining and can also interfere with the conversion of some nutrients to their active forms. Alcohol-induced disorders such as inflammation of the pancreas and small intestine and liver cirrhosis can also lead to malnutrition.

Vitamin A

Alcohol irritates the digestive tract and inhibits the absorption of vitamin A. It also depletes the body's tissue stores. Deficiency is common in alcoholics and contributes to some of the disorders of alcoholism such as night blindness, skin problems, cirrhosis of the liver and susceptibility to infections. Vitamin A supplements should not be taken with large amounts of alcohol as liver damage may occur.

B vitamins

Alcoholics are classically deficient in B vitamins, and supplements are sometimes used to treat alcoholics and those recovering from the disease. Deficiency is due to low dietary intake, impaired absorption and storage, and reduced conversion to the active form of the vitamin. Alcoholics and binge drinkers are especially prone to thiamin deficiency, which is associated with some of the symptoms of alcoholism such as mental confusion, visual disturbances and staggering gait. If thiamin deficiency is not corrected, permanent brain damage may result. This condition is known as Wernicke Korsakoff syndrome and is usually seen in people who have been addicted to alcohol for many years. Some experts recommend 100 mg of thiamin per day for those who drink alcohol.

Alcohol may increase niacin needs and nicotinamide has been shown to protect against the damage to liver cells caused by drinking a large quantity of alcohol.¹ Alcohol increases breakdown of the biologically active form of vitamin B6 and long-term use may cause liver damage which interferes with the conversion of vitamin B6 to the active form.

Antioxidants

Studies show that alcoholics have lower tissue levels of the antioxidants, beta carotene, vitamin E, vitamin C and selenium.² Increased oxidative damage to tissues also occurs as a result of heavy alcohol consumption. The higher needs and reduced intake put alcoholics at increased risk of diseases such as cancer and cardiovascular disease. Studies have also demonstrated that when those at risk cut their alcohol consumption, levels of antioxidants start to normalize.

Beta carotene

Drinking large amounts of alcohol may lower blood levels of carotenes.³ There have been several studies of the effects of beta carotene supplements on cancer and cardiovascular disease prevention. Some of these studies, including the Finnish Alpha Tocopherol Beta Carotene Cancer (ATBC) Prevention Study, the US Carotene and Retinol Efficacy Trial (CARET), have involved men who smoked and drank alcohol. The results of these studies suggest that beta carotene supplements increase the risk of cancer and cardiovascular disease in those who smoke and drink alcohol. This may be because beta carotene is susceptible to oxidative damage from alcohol and the gases in cigarette smoke, which may lead to the formation of harmful compounds. This suggests that heavy drinkers should not take beta carotene supplements. (See page 54 for more information.)

Vitamin C

Alcohol appears to increase vitamin C excretion and may lead to deficiency.⁴ Vitamin C is very important for alcoholics as it protects against oxidative damage and plays a role in the detoxification of alcohol.

Selenium

Alcoholics may have low levels of selenium, increasing the risk of liver damage. Selenium is part of the enzyme, glutathione peroxidase, which is important in protecting against the free radical damage which alcohol causes in the liver. A 1983 English study of selenium status in 391 healthy people showed that a combination of alcohol and smoking was most likely to lead to selenium deficiency.⁵

Vitamin D

Alcohol interferes with the conversion of vitamin D to its biologically active form. This can lead to abnormalities in vitamin D levels which disturb calcium and phosphate metabolism. This contributes to the high frequency of bone fractures and osteomalacia in alcoholics.

Magnesium

Alcoholics are at particular risk of magnesium deficiency. Alcohol causes an increase in the urinary excretion of magnesium and depletes body stores. Magnesium deficiency may exacerbate the symptoms of alcoholism such as high blood pressure, other cardiovascular diseases and osteoporosis.⁶ Supplements have been shown to have therapeutic effects in the prevention and treatment of these symptoms. Magnesium sulfate injections may help to diminish the severity of withdrawal symptoms in patients who have recently abstained from alcohol.⁷

Zinc

The enzymes needed for detoxification of alcohol contain zinc, and alcohol may also decrease dietary absorption and increase excretion of zinc. This leads to increased zinc requirements in those who drink a lot of alcohol. Zinc deficiency in alcoholism is likely to be linked to altered vitamin A metabolism, suppressed immune function, neurological problems, eye problems and sex organ abnormalities. Zinc deficiency may also play a role in fetal alcohol syndrome, birth defects associated with alcohol use by pregnant women.

Other minerals

Alcohol abuse also leads to calcium and potassium deficiencies with resulting harmful effects on the cardiovascular system, bones and other body tissues. Alcohol may exacerbate the liver damage caused by the iron overload disease, hemochromatosis, and sufferers should avoid drinking alcohol.

Tobacco

Smoking adversely affects a person's nutritional status in many ways. Cigarette smoke increases the damage caused by free radicals, which may explain the link between smoking and diseases such as cancer. Lung cancer causes more deaths than any other cancer and is strongly linked to smoking.

Antioxidants

Several studies have shown that levels of antioxidants are lower in smokers. Vitamin C needs, in particular, are increased. The RDA for smokers has been increased to 100 mg but needs may in fact be much higher. Despite this, smokers often eat diets which contain lower levels of vitamin C than those necessary to provide protection.

Vitamin C supplementation may help to protect against smoking-related damage. It may help to decrease the smoking-related build-up of atherosclerotic plaque by limiting the amount of white blood cells which stick to artery walls.⁸ In a German study done in 1996, supplements were effective in restoring reduced plasma vitamin C concentractions.⁹ Like those with high cholesterol levels and coronary heart disease, the arteries of smokers have a reduced ability to dilate. Vitamin C supplements may counteract this impairment.¹⁰

There have been several large trials examining the effects of antioxidant supplements in smokers. These include the CARET and ATBC studies, which recently reported that large doses of beta carotene may actually increase the risk of lung cancer in smokers. In the ATBC study, the adverse effects appeared stronger in men who drank alcohol and in those who smoked 20 cigarettes a day than in those who smoked less. This is confirmed by the CARET results which showed greater risk in current smokers than former smokers and also in those who drank alcohol. (See page 54 for more information.)

Tobacco smoke may damage beta carotene in ways which cause it to become harmful to body cells. Laboratory research shows that vitamin C may protect against these harmful effects suggesting that, in smokers, vitamin C supplementation should accompany beta carotene supplementation.¹¹ Vitamin E may also provide protection against the oxidative damage caused by cigarette smoke.

B vitamins

Cigarette smoke may cause a folic acid deficiency in the cells lining the lungs, making them susceptible to damage, which may lead to cancer. Folic acid may also help to prevent the pre-cancerous changes in lung tissue caused by smoking.¹² Heavy smoking may also inactivate vitamin B12.

Antacids

Antacids are commonly used to neutralize stomach acid in cases where excess causes pain. They are also used to treat a condition known as reflux esophagitis where the stomach acid comes up into the esophagus and causes painful inflammation of the membrane lining. This causes heartburn, indigestion or dyspepsia. Cigarettes, coffee, chocolate and fatty foods aggravate the condition. Most indigestion is related to dietary or alcoholic excess, and antacid use is fairly common.

Antacids contain a metal ion, aluminum, magnesium, calcium or sodium, linked to an alkali. Most antacids are a mixture of different ions which minimizes side effects. Long-term use of antacids that contain aluminum hydroxide may inhibit calcium absorption and increase the risk of calcium deficiency and bone disorders. Sodium-containing antacids interfere with calcium absorption and can increase the risk of high blood pressure. Regular use of calcium-containing antacids can be a good source of calcium in the diet but may lead to magnesium and chromium deficiency with long-term use.

As antacids reduce the acidity of the stomach environment, the activity of digestive enzymes is inhibited and absorption of nutrients which require an acid environment for absorption is reduced. These include iron, calcium, zinc, chromium, niacin, folic acid, vitamin A, thiamin and vitamin B12. This reduction in absorption of vitamins and minerals can be lessened if the antacid is taken on an empty stomach rather than with food.

Antibiotics

Antibiotics are widely used in the treatment of infections. Antibiotic-induced vitamin and mineral deficiencies are unlikely to be a problem if the diet is good and use is short-term.

Vitamins

Patients on long-term therapy with some antibiotics can develop deficiencies in some B vitamins, as intestinal bacteria that produce vital nutrients are killed along with the harmful bacteria. These deficiencies could have potentially serious effects, especially for elderly people, and supplements are helpful in preventing them. Long-term use of antibiotics may produce vitamin K deficiency and blood clotting disorders. Antibiotics can kill not only harmful bacteria but also the beneficial bacteria that produce vitamin K. Antibiotics may reduce vitamin C stores.

The antibiotic, isoniazid, which is often used to treat tuberculosis, can cause nerve damage due to its inhibition of vitamin B6 action. Patients with diabetes, malnutrition, or alcoholism may be at higher risk and supplements may be useful to protect against these problems. Several other antibiotics may adversely affect vitamin functions: neomycin interferes with the absorption of vitamin B12 and vitamin D; some antibiotics may cause niacin flushes to become more severe; trimethoprim can raise folic acid requirements; and chloramphenicol may interfere with the red blood cell functions of vitamin B12. There have been reports of benign intracranial hypertension during concurrent use of vitamin A and tetracycline.

Minerals

Tetracycline antibiotics reduce calcium, zinc, iron and magnesium absorption, and calcium salts and magnesium salts that are present in foods and dairy products can form chelates with tetracyclines and cause impaired absorption. The antibacterial efficacy of tetracyclines may be reduced by concurrent use of zinc salts such as zinc sulfate.

Neomycin affects calcium, iron and potassium absorption. Iron may decrease absorption of tetracyclines, penicillamine, ciprofloxacin or norfloxacin. Antibiotics can deplete potassium if taken long-term.

Anticancer medications

Malnutrition is a major cause of deterioration and death in cancer patients, and the effects of anticancer drugs may contribute to this. Good nutrition during chemotherapy can help people cope better with the side effects from the powerful drugs, fight infection more easily and speed recovery of healthy tissue. It is important that the diet includes enough calories to maintain weight and protein to build and repair tissues. A diet high in vitamins and minerals is also very important. In some cases, vitamin and mineral supplements may be useful. However, they should never be taken without a doctor's approval.

Several types of drugs may be used in combination with other types of therapy such as radiation or surgery. The type of therapy depends on the type of cancer, the location and extent and the patient's general health. Anticancer drugs may be given intravenously, intramuscularly, via catheters, topically or orally. It is important that a doctor is aware of any medications taken before chemotherapy is started or during treatment. This includes vitamin and mineral supplements.

Side effects vary from person to person and from drug to drug. Anti-cancer drugs are designed to kill fast-growing cancer cells and therefore also affect other body cells which are fast-growing, such as cells in the bone marrow, digestive tract, reproductive system and hair follicles. The most common side effects are hair loss, nausea and vomiting, fatigue, susceptibility to infection, and anemia. Recovery time depends on the type of treatment and general health.

Cancer chemotherapy has many side effects, including some nutritional ones. These powerful drugs often affect the digestive system and reduce the desire to eat. Common side effects include sore or dry mouth, altered taste sensation, nausea and vomiting. Diarrhea, constipation and reduced absorption are also common. Nausea and vomiting can be limited by avoiding big meals, eating and drinking slowly, avoiding fatty and sweet foods, and resting after eating.

Keeping mouth, gums and throat healthy can be helped by brushing gently with a soft, clean toothbrush. Mouth sores which prevent eating can be treated with medication. Eating soft, soothing foods, cold or at room temperature; and avoiding irritating, spicy, salty, acidic foods or rough dry foods can also help ease discomfort. Drinking plenty of water, using artificial saliva and sucking candy can help relieve a dry mouth.

If chemotherapy leads to diarrhea, potassium-rich foods are important. Low fiber foods, drinking plenty of water and avoiding fatty, spiced foods, tea, coffee and alcohol can be beneficial. Constipation can be relieved by drinking plenty of fluids, eating high fiber foods and exercising.

Chemotherapy can affect the bone marrow's ability to make red blood cells, leading to anemia. Getting plenty of rest and eating a diet rich in essential nutrients such as iron, folic acid and vitamin B12 can help lessen these effects.

The anticancer drug, methotrexate, alters folic acid metabolism. It acts by suppressing the multiplication of rapidly dividing cancer cells as these cells rely more heavily on folic acid. However, healthy cells also need folic acid and are affected by methotrexate. Folic acid supplements may be taken when on this drug but this should only be under medical supervision. Recent research suggests that long-term treatment with methotrexate also causes loss of bone mineral density.¹³ High doses of riboflavin can reduce the effectiveness of methotrexate.

Vitamin C

Some controversy surrounds the use of vitamin C in the treatment of cancer. The Nobel Prize winner, Linus Pauling and his colleagues have used vitamin C to improve survival times in cancer patients, but these results have not been repeated in other studies. Vitamin C may also benefit cancer patients who are undergoing radiation treatment by enabling them to withstand greater doses of radiation with fewer side effects.¹⁴

Zinc

Zinc supplements have been used to improve taste perception in people taking medications which reduce taste sensation and in cancer patients undergoing radiation therapy.¹⁵ This can be valuable in helping to maintain normal weight and nutrient intake during treatment.

Anticoagulants

Anticoagulant drugs such as warfarin decrease the clotting ability of the blood and are often used to treat heart problems. They act by interfering with the vitamin K-dependent clotting factors. Large doses of vitamin K may interfere with the action of these drugs and are not usually given to people who are taking them. Those taking anticoagulants should keep their intake of vitamin K foods relatively constant. Large doses of vitamin C may also affect the action of anticoagulants.

Vitamin E can enhance the action of anticoagulant drugs on blood clotting and should not be taken in very large doses. However, the results of a 1996 study in which 21 people taking chronic warfarin therapy received either vitamin E or placebo suggest that vitamin E can safely be given to patients who require chronic warfarin therapy.¹⁶

Anticonvulsants

Anticonvulsant drugs such as phenytoin, phenobarbital, primidone and carbamazepine are used in the treatment of epilepsy. These drugs can affect the metabolism of several vitamins and minerals.

Vitamin D

Long-term use of anticonvulsants may lead to a loss of calcium from bone due to the adverse effect of the medication on the manufacture of vitamin D. It is often recommended that anyone on long-term anticonvulsant therapy take a vitamin D supplement.

Folic acid

Phenytoin, phenobarbital and primidone interfere with the action of folic acid. This may lead to deficiency which can cause anemia and birth defects. Supplementation may be necessary, particularly in pregnant women, but large doses should be used with caution as they can interfere with the effectiveness of the drug and lead to seizure breakthrough. The increase in red blood cell production stimulated by folic acid may also increase the need for vitamin B12.

Vitamin K

Vitamin K levels may also drop on long-term anticonvulsant therapy and supplements are often recommended, particularly for pregnant women as a deficiency can result in an increased risk of hemorrhage in a newborn baby.

Others

Anticonvulsants may lower plasma vitamin E levels by altering absorption, distribution and metabolism. Copper and zinc levels may also be lowered by long-term anticonvulsant therapy.

Antidepressants

The long-term use of antidepressants can affect nutrient intake as these drugs often reduce appetite via effects on mood and the gastrointestinal system. They may also increase excretion of many nutrients. B vitamins (which are often low in those with depression), vitamin C, calcium and magnesium may be particularly affected and supplements may be beneficial in many people. The activation of riboflavin in the liver may be inhibited by major tranquilizers and some antidepressants. Supplements may be beneficial in those taking these drugs on a long-term basis.

Low folate levels have been linked to poorer response to the antidepressant drug, Prozac. In a study published in 1997, researchers examined the relationships between levels of folate, vitamin B12, and homocysteine in 213 depressed patients taking Prozac. The results showed that people with low folate levels were more likely to have melancholic depression and were significantly less likely to respond to the drug.¹⁷

Lithium

Lithium therapy can cause low sodium levels by reducing re-absorption by the kidney. Lithium should be used with caution in patients following low salt diets. Lithium may also affect calcium and magnesium metabolism and decrease bone mineral content.

Anti-inflammatory medications

The antigout drug, colchicine, reduces the absorption of vitamin B12, increases tissue loss of calcium and potassium and reduces the absorption of folic acid, iron and vitamin A. Nonsteroidal anti-inflammatory drugs (NSAIDS) may cause kidney damage, leading to high potassium levels.

Sulfasalazine can inhibit the absorption and lower the plasma concentrations of folic acid. Thiamin and riboflavin requirements may also increase. Indomethacin may impair vitamin C and thiamin metabolism.

Beta blockers

Beta blockers, which are used to treat high blood pressure and some other types of cardiovascular disease, have been shown to interfere with the production and function of coenzyme Q10, and to adversely affect heart function. This may explain why, in some cases, long-term therapy with beta blockers can lead to congestive heart failure. Coenzyme Q10 therapy in combination with beta blockers may be beneficial.

Corticosteroids

Corticosteroid drugs are widely used in medical treatment for autoimmune diseases such as arthritis, chronic obstructive lung disease, asthma and allergic conditions. Treatment with high doses of corticosteroids causes osteoporosis, particularly in the type of bone found in the lumbar spine.

Corticosteroid cause osteoporosis by several mechanisms; they decrease levels of sex hormones and also directly affect the cells which build and break down bone. They also decrease the absorption of calcium from the intestine. Corticosteroids may also raise folic acid, vitamin B6 and vitamin C requirements.

Vitamin D and calcium supplements may be useful in preventing bone loss in patients taking corticosteroids. In a 1996 study, researchers showed that calcium and vitamin D supplements can help prevent this loss. In the two-year study, 96 patients with rheumatoid arthritis, 65 of whom were taking corticosteroid drugs, were given 1000 mg calcium and 500 IU vitamin D per day or placebo. The researchers analyzed the bone mineral density of the lumbar spine and femur for one a year. In those patients taking corticosteroid drugs and placebo, losses of bone mineral density were seen. In those taking the supplements, gains were seen; and in those not taking corticosteroids, the supplements did not appear to affect bone mineral density.¹⁸

Arthritis medications

D penicillamine is used in severe and disabling rheumatoid arthritis. It may affect nutrient intake by causing loss of appetite and gastrointestinal disturbances. It can also reduce absorption of iron and zinc and should not be taken with foods containing these minerals. Experts suggest that at least a two-hour period should elapse between the administration of iron salts and oral penicillamine doses. Vitamin B6 needs may also be increased with long-term use of D penicillamine. Supplements in doses of 25 mg per day may be useful.

Aspirin

Aspirin is used as a painkilling and temperature-reducing drug. Frequent use of aspirin may cause bleeding in the stomach and intestines. This may lead to iron deficiency if aspirin is taken for long periods. Patients with vitamin K deficiency should use aspirin cautiously as increased bleeding may result. Vitamin A may protect against stomach ulcers and bleeding in those taking aspirin.

Aspirin may also lead to deficiencies of folic acid, thiamin, vitamin C, potassium and vitamin B12 if used for a long time. Calcium decreases the absorption of aspirin if taken at the same time. The nicotinamide form of niacin causes flushing when taken in large doses. This is caused by blood vessel dilatation, and pretreatment with aspirin may inhibit this effect, which some people find unpleasant.

Asthma medications

Long-term therapy with theophylline, a drug often given to asthmatic patients, lowers vitamin B6 levels. Vitamin B6 supplements may be useful in preventing the side effects of the drug which include headaches, nausea, sleep disorders and convulsions.¹⁹

Caffeine

Caffeine may increase calcium and potassium losses and reduce zinc absorption. This may contribute to disorders such as high blood pressure and osteoporosis. Caffeine may also raise thiamin requirements. Most studies suggest that the harmful effects of caffeine occur in those who drink more than two cups of coffee per day.

Cardiovascular disease medications

The effect of the heart stimulant drug, digoxin, can be toxic when magnesium and potassium concentrations are too low and when calcium is too high. However, digoxin may not be effective in patients with low calcium levels and small amounts of supplements may be necessary. It is recommended that serum potassium and calcium be monitored regularly in patients receiving digoxin. Digoxin may also lead to thiamin deficiency.

Cholesterol-lowering drugs

In recent years, the 'statin' drugs, lovastatin, pravastatin, and simvastatin have become widely used to treat high blood cholesterol. These medications work by inhibiting an enzyme known as HMG-CoA reductase, and they are very effective in lowering cholesterol levels. However, this enzyme is also responsible for production of coenzyme Q10. Because of this, the cholesterol-lowering effect of these drugs is accompanied by an equivalent lowering of coenzyme Q10 levels. In patients with existing heart failure, lovastatin has been shown to cause increased heart disease with life-threatening results in some patients. Coenzyme Q10 supplements may help to prevent some of the adverse effects of these widely used drugs.

The cholesterol-lowering drug, cholestyramine, reduces the absorption of fat soluble vitamins A, D, E and K, and may lead to deficiencies. Water soluble supplements of these vitamins may be useful. Folic acid, vitamin B12 and iron levels may also be adversely affected, leading to anemia. Cholestyramine may also increase calcium excretion. Colestipol may also lead to folic acid and fat soluble vitamin deficiencies. Niacin may increase the effectiveness of colestipol.

Diabetes medications

The antidiabetic drug, metformin, can inhibit the absorption of vitamin B12, leading to anemia. Other B vitamin deficiencies are also common in patients taking this drug. Niacin may affect the control of blood sugar in diabetics and should be used with caution in patients taking metformin.

Estrogen therapy

Estrogen-containing drugs include oral contraceptives and the hormones used in hormone replacement therapy (HRT). They are often used for long periods and can affect the absorption and use of several nutrients. Some of these effects are beneficial and others may be harmful.

Antioxidants

It has been suggested that estrogen can increase the risk of certain cancers, including those of the breast and cervix. These links have not been confirmed but some studies suggest that estrogen may increase free radical formation. If this is the case, antioxidant vitamin supplements may be useful in protecting against oxidative damage. Oral contraceptive use may also decrease vitamin C and beta carotene levels.²⁰ Large doses of vitamin C may cause higher blood levels of estrogen when taken at the same time as the contraceptive pill. It is best to take vitamin C supplements separately.

Calcium

HRT is used to increase bone mineral metabolism in postmenopausal women who are at risk of osteoporosis. Estrogen increases calcium absorption, decreases calcium excretion and increases vitamin D levels, thus improving the deposition of calcium into bone.

Folate

Some research suggests that there is a higher risk of abnormalities in cervical tissue in women using oral contraceptives. Supplements are beneficial in preventing cervical dysplasia in these women.²¹ (See page 585 for more information.)

Vitamin B6

As estrogen may affect vitamin B6 metabolism and increase needs,²² supplements may be beneficial for pregnant women, those on the contraceptive pill or those on hormone replacement therapy (HRT) who suffer from mood swings and depression. Vitamin B6 is sometimes known as the women's vitamin.

Other nutrients

Blood levels of vitamin B12, thiamin, riboflavin, magnesium and zinc may be lowered by the contraceptive pill. Copper and vitamin A levels may be raised. The contraceptive pill may reduce menstrual bleeding which decreases iron loss.

High blood pressure medications

There are various types of high blood pressure medications and these vary in their effects on vitamins and minerals. ACE inhibitors such as enalapril raise potassium levels. They should not be used with potassium supplements as heart problems can occur with excessive levels. People taking potassium sparing diuretics such as spironolactone should also avoid potassium supplements as body levels may become too high. Spironolactone may also reduce the availability of vitamin A. Loop diuretics such as bumetanide may cause excessive potassium loss and supplements may be necessary.

Low potassium levels is one of the most common adverse effects associated with thiazide diuretic therapy and can lead to cardiac arrhythmias. This effect is especially important to consider in patients receiving cardiac glycoside therapy (such as digoxin) because potassium depletion increases the risk of toxicity of this drug. Potassium supplements may be necessary in such cases, although they should be used cautiously in patients receiving digoxin. Thiazide diuretics may also decrease calcium excretion and increase magnesium excretion. Magnesium supplements may be useful in patients on long-term diuretic therapy. Zinc absorption may also be reduced. Hydralazine may increase the demand for vitamin B6 as it enhances excretion. Long-term use of frusemide may lead to thiamin deficiency.

Laxatives

Long-term use or overdosage can cause abdominal pain, nausea/vomiting, loss of weight, muscle weakness, laxative dependence, and low potassium and calcium levels. Mineral oil laxatives bind fat soluble vitamins and reduce absorption.

Osteoporosis medications

Taking oral etidronate with vitamin and mineral supplements that contain calcium salts, iron salts such as ferrous sulfate or magnesium salts may be inadvisable. These salts can interfere with the absorption of etidronate, and should not be taken within two hours of the drug. Even though calcium salts should not be taken at the same time as etidronate, patients need to maintain an adequate intake of calcium and vitamin D to avoid low calcium levels.

Psoriasis medications

The vitamin D-derivative drug, calcipotriene, should not be used with high doses of vitamin D and calcium.

Thyroid medications

Excess intake of iodine/iodide can decrease the efficacy of propylthiouracil.

Sedatives and tranquilizers

Barbiturate drugs may enhance excretion and metabolism of vitamin C, and reduce the conversion of vitamin D to its active form.

Vitamin A-derivative drugs

Vitamin A supplements should not be used with the vitamin A-derivative drugs tretinoin, isotretinoin and etretinate. These drugs are used to treat skin disorders such as acne and can be toxic if taken with high levels of dietary vitamin A.

Top