What are the side effects of multivitamins?

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People use multivitamins for several different reasons. Some people have naturally occurring deficiencies from various diseases or a poor diet. A multivitamin can return needed nutrients to the body.

In other cases, people take multivitamins because they want extra doses of certain vitamins that are reported to help the immune system, memory or overall health. Multivitamins also provide people with vitamins that are difficult to find naturally in food. A multivitamin allows you to ingest everything at once without having to search the grocery store for a bunch of missing pieces. Yet even though multivitamins have many potential health benefits, certain side effects can occur through improper use, allergy or intolerance.

Serious Side Effects

Many of the most serious side effects of taking multivitamins result from vitamin overdose due to ingestion of too much of a given mineral. Calcium, iron and zinc are all necessary for the human body to function properly, but too much of any of these minerals in the bloodstream can lead to serious complications such as heart palpitations, stomach bleeding, confusion, tooth stains and increased urination. Even more serious is an overdose on Vitamins A, D, E or K. A serious overdose of these vitamins can even be life threatening. Early warning signs of vitamin overdose include weight loss, splitting headache, menstrual changes, intense back pain or easy bruising. While it's possible for someone to overdose on a relatively small amount, the chances of overdose increase with the amount of multivitamins taken. Just because one a day is good for you, don't assume three a day must be better. It's not.

Mild Side Effects

Multivitamins taken on an empty stomach can lead to gastrointestinal disruptions including queasiness, constipation and diarrhoea. Other common, but less serious, side effects include slight headache and a lingering foul taste in your mouth. The foul taste is more likely if you take your vitamins without food or don't swallow them fully. Multivitamins also can cause sleep problems, especially if taken right before bed. To reduce the risk of unpleasant side effects, take your vitamin in the morning with breakfast or in the afternoon with lunch.

Allergic Reaction Side Effects

Since multivitamins contain so many vitamins and minerals, allergic reactions are certainly possible. Mild allergic reactions can include itchiness and a few hives. If you experience these side effects, stop use and contact your doctor. Should you experience more advanced signs of an allergic reaction or anaphylactic shock, such as trouble breathing, chest pain, widespread hives or a swollen facial region, visit the closest emergency room immediately.

Vitamin Interactions

Additional side effects are possible if you take other medications. Some of the medications known to react negatively with multivitamins include diuretics, blood pressure medication, tretinoin, trimethoprim and ibuprofen. This doesn't necessarily mean you can't take a multivitamin with these medications. Just check in with your doctor. A shift in dosage may be necessary. In addition, dairy and other calcium products can interfere with the body's absorption of various vitamins and minerals. Again, consult your doctor if you take calcium supplements, antacids with calcium or have a diet high in dairy.

Multivitamins and pregnancy

Multivitamins can be an excellent source of nutrition for pregnant women and their babies, but certain minerals found in multivitamins should be avoided in high doses. Pregnant women, women attempting to get pregnant, and nursing women should not take any multivitamins that contain more than 100 per cent of the recommended daily value of these vitamins and minerals. If you are pregnant, discuss your prenatal vitamins with your doctor.

Other Risk Factors

People with pre-existing medical conditions may not respond well to some of the vitamins in certain multivitamins. Again, discuss this with your doctor before you go forward with any particular course of vitamins. If a multivitamin contains both iron and calcium, the iron may prevent full absorption of the calcium. Therefore, it's advised to take a separate calcium supplement either earlier or later in the day than the multivitamin. Similarly, too much vitamin C in a multivitamin (more than 500 mg) will prevent the proper absorption of vitamin B12.