If you suffer from a vitamin deficiency, a diverse diet and supplements can help your body get back on track. However, before you begin any new regimen, it's important to realize that anything you put into your body can have adverse effects. The risk of a reaction is even higher if you take more than one supplement at a time, or if you pair your supplements with over-the-counter (OTC) or prescribed medications.
"As we know, there are plenty of supplements that are synergistic when combined versus those that actually can increase side effects, or increase or decrease absorption," Azza Halim, MD, a board-certified anesthesiologist who also specializes in anti-aging and regenerative medicine, tells Best Life. She adds that you may still be able to pair these supplements with your doctor's approval and oversight, but that you should take them at least a few hours apart to avoid interaction.
Your best bet for safety is to have your doctor or pharmacist review your proposed supplement regimen before you get started. However, the following supplement pairs generally raise red flags and are considered best avoided.
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1 | Calcium and iron
iStockOne of the most common reasons that supplements might make a poor pairing is if they cancel one another out. Trista Best, MPH, RD, a registered dietitian at Balance One Supplements, says that calcium and iron are a perfect example of how you can undermine the benefits of supplements by combining the wrong things.
"You'll want to avoid taking your iron supplement with a calcium supplement or food source," says Best. "These two vitamins compete for absorption, and calcium will reduce the amount of iron your body is able to absorb, if any."
To maximize your body's absorption of an iron supplement, Best instead recommends pairing it with vitamin C.
"Non-heme iron comes from plant sources and it isn't absorbed as easily as heme forms, but adding vitamin C can increase iron's absorption. This can be done simply by adding lemon to your water or eating some strawberries along with your supplement regimen," she says.
2 | Zinc and copper
iStockMany people favor zinc and copper supplements to boost their immune systems. However, certified nutritionistJenny Dobrynina says that taking them at the same time will produce ineffective results.
"Combining copper and zinc is not advisable because they compete for absorption in the body. So, taking them together reduces their effectiveness," she tells Best Life.
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3 | Vitamin C and vitamin B-12
Shutterstock / pikselstockDobrynina also warns against taking vitamin C and vitamin B-12 at the same time: "I recommend taking these two supplements at least two hours apart."
According to the Mayo Clinic, taking the two supplements simultaneously can lead to reduced levels of vitamin B-12 in the body. A B-12 deficiency can cause anemia, or a reduction in healthy red blood cells, ultimately leading to fatigue, breathlessness, balance problems, memory impairment, and more.
4 | Vitamin E and vitamin K
iStockNext, Dobrynina warns against taking vitamin E and vitamin K at once, since they can have opposing effects on coagulation.
"Studies show that vitamin E supplementation leads to increased bleeding in some people. Doctors usually prescribe vitamin K supplements to help with blood clotting. So, taking vitamin E simultaneously with vitamin K can counteract the effects of vitamin K," she explains.
A 2023 case study published in the Journal of Medical Case Reports corroborates that high doses of vitamin E "inhibit vitamin K-derived coagulation factor synthesis, which can cause serious bleeding events such as gastrointestinal bleeding and intracranial hemorrhage."
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5 | Fish oil and ginkgo biloba
iStockJacek Szymanowski, a Precision Nutrition-certified nutritionist and health coach, says that the combination of fish oil and ginkgo biloba can also affect your blood's ability to clot safely.
"Combining these can increase the risk of bleeding due to their blood-thinning effects. Both supplements have anticoagulant properties, which can synergistically increase bleeding risk, especially in high doses or with other blood thinners," he explains.
6 | Folic acid (vitamin B9) and vitamin B-12
iStockIf you take folic acid and vitamin B-12 together, this is another pairing that you may want to re-evaluate with your doctor's help. Dobrynina warns that "excess consumption of vitamin B9 and B-12 (folic acid and folate) can hide the symptoms of vitamin B-12 deficiency."
Studies have indicated that in rare instances, this could cause neurological damage. "There is a risk that if folic acid is given to people who have undiagnosed deficiency of vitamin B12 it may lead to neurological damage," says one study published in the Cochrane Database of Systematic Reviews.
"Vitamin B12 deficiency produces both an anemia identical to that of folate deficiency but also causes irreversible damage to the central and peripheral nervous systems. Folic acid will correct the anemia of vitamin B12 deficiency and so delay diagnosis but will not prevent progression to neurological damage," the researchers write.
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Best Life offers the most up-to-date information from top experts, new research, and health agencies, but our content is not meant to be a substitute for professional guidance. When it comes to the medication you're taking or any other health questions you have, always consult your healthcare provider directly.
