Calcium and Magnesium Don't Mix, Along With These 6 Other Supplement Combinations

While supplements can be beneficial for people who need them, taking certain supplements together can lead to unwanted health issues.

By Allison Futterman; Medically Reviewed by Dr. Ahmad Talha Azam
Feb 19, 2024 4:00 PM
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(Credit: Kmpzzz/Shutterstock)

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Almost 75 percent of Americans take dietary supplements, with more than half doing so on a regular basis. While these supplements can benefit people with deficiencies, certain combinations can cause health problems. 

While some supplements work better when taken simultaneously, creating a synergistic effect — others should not be combined. Whether because of absorption issues or possible harm, it’s best to wait at least two hours between certain supplements for safety reasons.

1. Calcium and Magnesium

Magnesium has a multitude of health benefits, including relieving constipation and having a positive effect on heart health. Calcium is needed for bone growth and maintenance, and also plays a role in blood clotting, muscle contraction and relaxation. 

Taken together, they both become less effective since they compete for absorption. However, spacing them apart by taking calcium with a meal and taking magnesium at night is a way to ensure the supplements don’t interact.

2. Iron and Green Tea

Iron plays a role in hemoglobin production, immune system support, pregnancy health, increased energy, and improved athletic performance. And green tea is high in antioxidants and offers health benefits that include reduction of inflammation, protection from oxidative stress, and the potential to lower blood sugar and reduce cancer risk.

Because green tea inhibits iron absorption, it's best not to take iron and green tea simultaneously, whether as a supplement or a drink. 


Read More: What You Should Know About Magnesium Supplements


3. Vitamin C and Vitamin B12

Although vitamin C is best known for supporting the immune system, it also helps to heal wounds and repair bones. While it works in conjunction with other supplements, such as iron and zinc — the opposite is true with vitamin B12

High doses of vitamin C actually impedes the absorption of B12. Since B12 is needed for red blood cell formation, nerve function, cell metabolism, and the repair of body tissues, you don’t want to diminish the maximum potential benefit by diminishing its effectiveness. 

4. Fish Oil and Ginkgo Biloba 

Omega-3-rich fish oil supplements are touted for reducing triglyceride levels, blood pressure, and inflammation. It’s also believed they may protect skin and eye health.

Ginkgo biloba is used to treat cognitive impairment, to reduce symptoms of dementia and Alzheimer’s disease, as well as help alleviate depression and anxiety. Together, fish oil and Ginkgo biloba both have blood-thinning properties and can increase the risk of bleeding or prevent blood clotting.


Read More: What You Need to Know About Vitamin C, Vitamin B, Turmeric, and Fish Oil/Omega-3


5. Copper and Zinc

Copper is key in the formation of red blood cells, bone, and connective tissue — while zinc plays a central role in immune function, wound healing, and sense of smell and taste.

Many people don’t realize that when taken in large amounts, zinc can deplete the copper in our bodies — creating a need for copper supplements. Since they’re both absorbed by the small intestine, they should be spaced out so as to not compete for absorption.  

6. Vitamin E and Vitamin K

Vitamin E has antioxidant properties that help control free radicals, which are related to oxidative stress. But vitamin E can also have a blood-thinning effect, impeding the body’s ability to clot properly.

Conversely, vitamin K increases blood clotting properties — in particular, the protein prothrombin. Because vitamin E can counteract the clotting effect of vitamin K, it can lead to coagulation issues and bleeding. 

7. Vitamin C and Copper

While maintaining a sufficient amount of copper is important for optimal health — it can be difficult to find just the right level. Too much can cause negative effects, and too little could lead to problems with bone strength, iron transport, glucose metabolism, and more.

Vitamin C is also essential for good health. But when taken together, they can result in the Fenton reaction, which leads to highly reactive hydroxyl radicals. These can cause kidney damage.

Before taking certain supplements, it's always best to consult a healthcare professional first.


Read More: Here’s Why You May Want To Take Vitamin D and Magnesium Together


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