What Vitamins Should Not Be Taken Together?

Reviewed on 12/3/2021

Some vitamins that should not be taken together, or have dosage limitations, include vitamin C with vitamin B-12, vitamin A supplement with vitamin A-rich foods, folic acid (vitamin B9) and vitamin B12, and vitamin E with vitamin K.
Some vitamins that should not be taken together, or have dosage limitations, include vitamin C with vitamin B-12, vitamin A supplement with vitamin A-rich foods, folic acid (vitamin B9) and vitamin B12, and vitamin E with vitamin K.

Many people take supplements to improve their health or prevent disease. In the United States, supplements are not regulated by the Food and Drug Administration. This means they do not come with strict instructions to follow or warnings about interactions like prescription medications.

So, you have to pay attention to which supplements you are taking, when you take them, and how much you take.

Vitamin combinations to avoid

Vitamin C with vitamin B-12

Vitamin C is an essential antioxidant for immune system health. Vitamin B-12 helps maintain your nervous system and form red blood cells. Studies show that taking these two supplements at the same time may reduce the amount of vitamin B-12 that you receive. So, experts recommend taking these supplements at least two hours apart.

Vitamin A supplement with vitamin A-rich foods

Since vitamin A is a fat-soluble vitamin, any excess is stored in the body. So, you don't need to take vitamin A every single day. Too much vitamin A can lead to weaker bones and more bone fractures as you age. It can also be harmful to unborn babies.

If you are pregnant or take a vitamin A supplement, avoid eating liver or liver paté. These foods are so high in vitamin A that even if you do not take a vitamin A supplement, you should only eat them once a week to avoid consuming too much.

Folic acid (vitamin B9) and vitamin B12

While both of these B vitamins are important, taking too much folic acid or folate can actually hide the symptoms of a vitamin B12 deficiency. So, speak to your doctor to verify your vitamin levels before adding these supplements to your regimen.

Vitamin E and vitamin K

It is well documented that vitamin E supplementation can lead to increased bleeding in some people. Some doctors prescribe a vitamin K supplement to help with blood clotting. Taking vitamin E at the same time can counteract the effects of vitamin K.

Other supplement combinations to avoid

Copper and zinc

Both copper and zinc are important minerals. Most people get enough of these nutrients through their diet. Copper helps with brain development, nervous system health, and in making important tissues in the body. Zinc is an important mineral for healing.

Different minerals can compete for absorption in your digestive system when taken at the same time. So, if you take copper and zinc together, one usually has poor absorption. In the case of these two supplements, zinc wins. People who take a lot of zinc supplements may develop a copper deficiency.

One source of zinc supplementation is denture cream. If you use denture cream and experience neurological problems, you may have a copper deficiency.

Green tea and iron

On their own, both of these supplements offer a lot of benefits. Green tea has anti-inflammatory compounds that may help people with conditions like inflammatory bowel disease. Iron is important for making hemoglobin, a protein in your blood.

However, when taken together, the antioxidants from green tea bind to iron. This lessens the positive effects of consuming green tea.

Calcium with other minerals

Calcium is an important mineral for bone health. Taking a calcium supplement can affect how your body absorbs other minerals including zinc, magnesium, or iron. If you take any combination of these supplements, talk to your doctor about the best timing for maximum absorption of each mineral.

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Vitamin, supplement, and medication interactions

In addition to having interactions with other supplements, some prescriptions interact with supplements. If you regularly take any prescription medications, always talk to your doctor before adding any new supplements to your routine.

Blood thinners

Vitamin A and vitamin K can have negative interactions with blood thinners, so you should avoid taking both.

Some herbal remedies can also interact with the blood thinner warfarin (Coumadin) including:

Drugs to treat heart disease

High doses of vitamin D can interact poorly with drugs to lower cholesterol and blood pressure, as well as some other drugs used to treat heart disease.

St. John's wort is an herbal supplement that has been used for hundreds of years to treat mental health issues. It has a potential interaction with several drugs that treat cardiovascular disease symptoms like high blood pressure or high cholesterol. If you take Digoxin, Verapimil, or any statin, check with your doctor to manage this combination.

Additionally, black cohosh, an herbal remedy for gynecological issues, can reduce how well statins work.

Psychiatric medications

You may have side effects when combining certain supplements with antidepressants and anti-anxiety medications.

  • Taking gingko with trazodone can lead to behavioral or emotional changes.
  • The combination of ginseng and monoamine oxidase inhibitors can cause manic symptoms.
  • St. John's wort may cause drowsiness when combined with SSRIs.
  • St. John's wort can also interfere with the absorption of benzodiazepines.
  • Milk thistle may affect how well you absorb diazepam (Valium).

Overall drug interactions

Two herbal supplements, St. John's wort and Goldenseal, have such a high risk of interactions, that many experts recommend avoiding them entirely if you take any prescriptions.

General supplement safety

Only some supplements have been researched and proven effective. For other supplements, more research is needed to find out if they work. Whether or not they are effective, they are usually safe to take. Follow these tips to stay safe with supplements.

  • Do not use supplements to replace a balanced diet.
  • Ask your doctor how much of a supplement to take if you're not sure. You may experience negative side effects after taking too large of a dose of certain supplements.
  • Always tell your doctor about all supplements you take before any surgery or procedure.
  • Use government or non-profit organization websites to research supplement claims.
  • Report any adverse supplement reactions to the FDA.

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References
American Family Physician: "Common Herbal Dietary Supplement–Drug Interactions," "Herbal and Dietary Supplement–Drug Interactions in Patients with Chronic Illnesses."

Harvard Health Publishing: "Nutrition's dynamic duos."

Mayo Clinic: "Can you tell me what I should eat while I am taking warfarin (Coumadin, Jantoven)? What foods should I avoid?" "When should I take calcium supplements? Does the timing matter?" "Vitamin A," "Vitamin B-12," "Vitamin D," "Zinc."

National Center for Complimentary and Integrative Health; "St. John's Wort and Depression: In Depth."

NHS: "Vitamin A."

National Institutes of Health: "Copper," "Iron," "Vitamin C."

Nutrition Reviews: "Vitamin E and K interactions – a 50-year-old problem."

Penn Medicine: "The Truth About Supplements: 5 Things You Should Know."

Penn State: "Green tea and iron, bad combination."

Proceedings of the Nutrition Society: "Folate and vitamin B12: friendly or enemy nutrients for the elderly."

U.S. Food & Drug Administration: "What You Need to Know about Dietary Supplements."

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