What vitamins should not be taken together?

Supplementation can be an effective way to fill any nutrient gaps in your diet, but research indicates that you could do more harm than good if they are taken incorrectly. Here’s what you need to know about what vitamins should not be taken together.

Whether you’re looking to boost energy, achieve glowy skin, balance hormones, or support healthy aging, chances are you’ve turned to supplements to achieve results and enhance your overall health. Supplements are not the end-all-be-all to optimal health and wellness, however, they are a good health insurance policy for bridging any nutritional gaps in your diet. 

However, not all supplements are created equal--while some are supported by science, others can negatively interact when taken incorrectly. So, how can you distinguish the good from the bad to determine what (and if) supplements are right for you?

Before we break down the vitamins you shouldn’t take together, let’s first discuss the importance of supplementation and why it can be useful.

Disclaimer: Supplements can have a range of contraindications, and may not be appropriate for everyone. Talk with your doctor or dietitian before adding a new supplement to your routine.

The importance of supplements

Despite your best efforts, you may not get all of the daily nutrients you need from a healthy, well-balanced diet. In fact, surveys show that only 10% and 12% of adults meet the daily fruit and vegetable intake recommendations, respectively, and that over 90% of the US population does not meet the daily requirement for vitamins A, C, D, and E, as well as for magnesium and calcium [





That’s why experts suggest that supplementation can be a reasonable solution for filling these nutrient gaps. And while supplements should never replace food, they can effectively treat nutritional deficiencies and bridge any nutrition shortfalls. Additionally, supplements can also benefit certain groups and individuals with certain conditions. For example, research shows that

alpha lipoic acid

can be beneficial for cholesterol reduction, and

vitamin C

may reduce the duration of the common cold [





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With so many supplements on the market, it can be hard to sort through the noise to determine which one is right for you. At Elo, we’ve done the work for you – our team of experts have dug into the science to determine the best supplements that will help you reach your health and wellness goals.

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Importance of third-party testing

Unlike food, supplement regulation is largely in the hands of manufacturers, and FDA approval for supplements is only required when the product contains a new ingredient. 

According to the FDA, every dietary supplement needs to be labeled with the term "dietary supplement" or with a term that substitutes a description of the product's dietary ingredient(s) for the word "dietary" [


]. However, federal law states that supplements don’t need to be FDA-approved before they are marketed, which means that the manufacturer or seller can add inaccurate or untruthful claims to supplements. 

That’s why you should always choose a supplement that has been third-party tested to help ensure purity, dosage, and freshness. Learn more about

Elo Health’s third-party testing process

in this article.  

It’s also important to note that some supplements may contain ingredients that can interact with medications, so speak with your healthcare provider before starting a new supplement [



What vitamins should not be taken together?

While supplementation can be an effective way to fill any nutrient gaps, there are certain ones that you should avoid taking together. Here are some common ones to watch out for.

Iron + calcium

When taken at the same time,




bind together and significantly reduce absorption [


]. Since iron is best absorbed when taken on an empty stomach and in the presence of

vitamin C

, it’s recommended to take it at least 2-3 hours before or after a calcium supplement. 

Vitamin C + B12

Experts suggest that when taken together, vitamin C could break down

vitamin B12

in your digestive tract and reduce absorption [


]. To avoid this interaction, wait 2-3 hours to take vitamin C after your B12 supplement.  

Potassium, calcium, zinc, and magnesium

If taken at the same time, large doses of these mineral supplements can compete for absorption and will not be as effective. If you take more than one mineral supplement, take them separately and at least two hours apart.

Green tea extract + iron

Green tea

contains a compound that binds to iron. When consumed together, green tea extract loses its antioxidant potential, and iron absorption is severely reduced [



To avoid this, consider taking green tea supplements two hours before or after eating iron-rich foods like meat, poultry, shellfish, beans, tofu, and fortified breakfast cereals. 

Multivitamin + calcium, zinc, magnesium, or potassium

Single mineral supplements (including calcium, zinc, and


) may interfere with the absorption of smaller minerals found in a multivitamin, like iron and zinc. 

For optimal absorption and maximum benefit, take your multivitamin a minimum of 2-3 hours before a calcium, zinc, magnesium, or potassium supplement.

Vitamins D, E + K

Some evidence suggests that moderate to large doses of the fat-soluble vitamins (specifically vitamins D, E, and K) may compete for and reduce absorption when taken together. The absorption of vitamin K seems to be most affected in the presence of other fat-soluble vitamins [



Take these supplements at least two hours apart and with some sort of dietary fat to optimize absorption. 

Copper + zinc

Though rare, copper deficiency can result from high levels of zinc, which decreases the body’s ability to absorb and use copper from the diet [


]. If you’re taking a daily zinc supplement, you should consider a copper supplement as well to avoid the potential for copper deficiency. However,  don't take them simultaneously; wait at least 2 hours after taking zinc to take your copper supplement. 


Supplements can often be touted as the end-all-be-all when it comes to health, but they are not all created equal. While some are supported by science, others can negatively interact when taken incorrectly. 

At Elo Health, we determine the right supplements for you based on your biomarkers and wearable data so you can reach your goals and avoid any nutrient interactions. As always, be sure to talk with your healthcare provider before starting a supplement routine or adding certain ones into your regimen.

Disclaimer: The text, images, videos, and other media on this page are provided for informational purposes only and are not intended to treat, diagnose or replace personalized medical care.

Key takeaways

  • While supplements can effectively treat nutritional deficiencies and bridge any nutrition shortfalls, some can negatively interact with each other when taken incorrectly.

  • Elo Health provides

    personalized smart supplements

    made just for you through

    at-home blood testing



    , and data from wearables.

  • Smart Supplements have been third-party tested to help ensure purity, dosage and freshness. 


  1. Centers for Disease Control and Prevention. (2022, January 6). Adults meeting fruit and vegetable intake recommendations - United States, 2019. Centers for Disease Control and Prevention.



  2. Micronutrient inadequacies in the US population: An overview. Linus Pauling Institute. (2023, January 3).



  3. Mousavi, S. M., Shab-Bidar, S., Kord-Varkaneh, H., Khorshidi, M., & Djafarian, K. (2019). Effect of alpha-lipoic acid supplementation on lipid profile: A systematic review and meta-analysis of controlled clinical trials. Nutrition (Burbank, Los Angeles County, Calif.), 59, 121–130.



  4. Common colds: Does vitamin C keep you healthy? (n.d.).



  5. FDA. FDA 101: Dietary supplements. U.S. Food and Drug Administration.



  6. FDA. Mixing medications and dietary supplements can endanger your health. U.S. Food and Drug Administration.



  7. Lönnerdal B. (2010). Calcium and iron absorption--mechanisms and public health relevance. International journal for vitamin and nutrition research, 80(4-5), 293–299.



  8. Mayo Foundation for Medical Education and Research. (2023, August 10). Vitamin B-12. Mayo Clinic.



  9. Fan F. S. (2016). Iron deficiency anemia due to excessive green tea drinking. Clinical case reports, 4(11), 1053–1056.



  10. Goncalves, A., Roi, S., Nowicki, M., Dhaussy, A., Huertas, A., Amiot, M.-J., & Reboul, E. (2015). Fat-soluble vitamin intestinal absorption: Absorption sites in the intestine and interactions for absorption. Food Chemistry, 172, 155–160.



  11. Munk, D. E., Lund Laursen, T., Teicher Kirk, F., Vilstrup, H., Ala, A., Gormsen, L. C., Ott, P., & Damgaard Sandahl, T. (2022). Effect of oral zinc regimens on human hepatic copper content: A randomized intervention study. Scientific Reports, 12(1).