which vitamins should you not take together

March 17, 2025

Medically Reviewed by By Girish Desai, the Chief Pharmacist at Landys Chemist since 1982.

Written by Rhysa Phommachanh Head of Digital Marketing

What Vitamins Should You Not Take Together? | Vitamin Guidelines

Taking vitamins and minerals together can be beneficial for the most part as some nutrients work better when combined, boosting each other's effectiveness. However, it's important to note that there are some combinations that you should generally avoid. In some cases, mixing certain vitamins and minerals can stop the body from absorbing them properly and reduce their effectiveness.

That said, for most people, taking vitamins and minerals is safe and can be an important way to fill any nutritional gaps in your diet. Supplements can help support overall health and make sure your body has the nutrients it needs to function well.

In this blog, we’ll look at which vitamins and minerals that shouldn’t be taken together, explain why these combinations can cause problems, and provide tips on how to take your supplements for the best results!

vitamins you should not take together

Vitamins That Should Not Be Taken Together

Below are the most important pairings you should avoid, based on research:

Calcium and Iron

Calcium can inhibit the absorption of non-heme iron (from plant-based sources and supplements). Studies have shown that calcium competes with iron for absorption in the intestines, potentially reducing iron uptake.
Recommended Approach: To enhance iron absorption, take iron supplements on an empty stomach or with vitamin C, and consume calcium supplements at a different time, later in the day

Vitamin C and Vitamin B12

High doses of vitamin C may lower vitamin B12 levels in the digestive tract, potentially lowering its effectiveness. A 1974 study found that high doses of vitamin C destroyed high amounts of vitamin B12 when ingested with food.
Recommended Approach: Space out vitamin C and B12 supplements by at least two hours to minimise potential interactions.

Vitamin K and Vitamin E

High doses of vitamin E may interfere with vitamin K's role in blood clotting, potentially increasing bleeding risk. A case report highlighted that high-dose vitamin E intake could inhibit the synthesis of vitamin K-dependent coagulation factors, leading to the risk of serious bleeding.
Recommended Approach: While vitamin K and E can be taken on the same day at different times, the NHS recommends a daily intake of 4mg of vitamin E for men and 3mg for women, while the recommended daily intake of vitamin K is 1 microgram per kilogram of body weight, equating to around 70 micrograms for a 70kg adult.

Zinc and Copper

Excessive zinc intake can inhibit copper absorption, potentially leading to a deficiency over time. A study found that zinc promotes the production of a copper-binding ligand in the gut, which traps copper and reduces its availability for absorption. This mechanism can lead to copper deficiency.
Recommended Approach: If supplementing with both zinc and copper, it's best to take a supplement that contains 8-10 mg of zinc for every 1mg of copper, or take them at separate times of the day to avoid interference. Read more about taking zinc and copper together here.

Calcium and Magnesium

Calcium and magnesium compete for absorption in the gastrointestinal tract, which can reduce their effectiveness when taken together. A study found that calcium directly or indirectly competes with magnesium for intestinal absorption and transport. This competition suggests that high intake of one mineral may impair the absorption of the other.
Best Practice: Take calcium supplements in the morning and magnesium in the evening, especially if using magnesium for relaxation or sleep, to optimise absorption.

Vitamin Interaction Guidelines

Vitamin	Interactions/Concerns	Recommendations
Iron	Coffee and green tea can inhibit the absorption of non-heme iron.	Avoid drinking coffee or green tea for at least an hour before or after taking iron supplements.
Vitamin D	Too much calcium can inhibit vitamin D absorption; vitamin D also affects calcium metabolism.	Take vitamin D3 with K2 to avoid too much calcium buildup and ensure proper calcium absorption.
Vitamin K	High doses of vitamin K can interfere with blood thinners, reducing their effectiveness.	Maintain consistent intake of vitamin K if on blood thinners and avoid large fluctuations.
Zinc	Excessive zinc intake can block copper absorption, leading to a deficiency.	Take zinc and copper at separate times or in a balanced ratio (8-10 mg of zinc for every 1 mg of copper).
Magnesium	Magnesium can interfere with the absorption of certain antibiotics.	Space magnesium supplements at least 2-3 hours apart from antibiotics.
Vitamin A	High doses of vitamin A can interfere with the absorption of vitamin D.	Take vitamin D3 with vitamin A in moderate doses, or space them apart.
Calcium	Excessive calcium can bind to phosphorus and reduce absorption.	Space out calcium and phosphorus intake to avoid absorption interference.
Vitamin C	High doses of vitamin C can degrade vitamin B12 in the digestive tract.	Space vitamin C and B12 supplements by at least two hours to minimise potential interactions.
Folic Acid	High doses of folic acid can mask a vitamin B12 deficiency.	Ensure adequate B12 intake when supplementing with high doses of folic acid.

Taking Multivitamins & Individual Supplements Together

Multivitamins often contain various vitamins and minerals, including iron, calcium, magnesium, and zinc. Taking additional high-dose individual supplements of these nutrients may lead to excessive intake, increasing the risk of adverse effects.

It’s important to look at the nutrient content of your multivitamin to avoid exceeding recommended daily vitamin and mineral dosages.

Supplements to Be Cautious About When on Medication

Certain supplements can interact with medications and cause harm. Here are key combinations to be aware of:

Blood Thinners & Supplements: Garlic, ginkgo biloba, vitamin E, and CoQ10 can increase bleeding risk when combined with blood thinners like warfarin or aspirin.
Licorice & Blood Pressure Medications: Licorice can raise blood pressure and interfere with hypertension medications.
ACE Inhibitors & Potassium Supplements: ACE inhibitors (e.g., ramipril) can increase potassium levels. Avoid potassium supplements to prevent hyperkalemia.
Thyroid Medications & Supplements: Iodine, calcium, and iron can reduce the effectiveness of thyroid medications. Take thyroid meds on an empty stomach and space supplements by at least 4 hours.
St. John’s Wort & Medications: St. John’s Wort can reduce the effectiveness of medications like antidepressants, birth control, and HIV treatments. It also increases the risk of serotonin syndrome.

Other Interactions That Need Considerations

Iron & Coffee / Green Tea

Coffee and green tea contain polyphenols that can inhibit the absorption of non-heme iron, reducing its effectiveness, especially in people with iron deficiency. To maximise iron absorption, avoid drinking coffee or green tea for at least an hour before or after taking iron supplements.

How long should you wait between different vitamins?

As a general rule of thumb, it’s recommended to wait at least 2 hours between taking different vitamins and supplements, especially if they have absorption interference (like calcium and iron, or vitamin C and B12). This spacing allows each nutrient to be absorbed efficiently without competing with others. For some combinations, such as vitamin D and vitamin K, you can take them together, especially if they complement each other (like in the case of fat-soluble vitamins).

However, for best results, it’s ideal to space out high-dose supplements or minerals that compete for absorption, like zinc and copper, or calcium and magnesium.

"Spacing out your supplements can help maximise absorption and ensure that each nutrient is used efficiently by your body." – Mitesh Desai, Nutritionist at Landys Chemist

FAQ

Can I take 5 different vitamins at once?

It’s possible to take multiple vitamins at once, but it’s important to consider potential interactions. For example, high doses of iron and calcium should not be taken together as calcium can reduce iron absorption. If you're taking a multivitamin along with individual supplements, ensure that you're not exceeding the recommended daily dosage for each nutrient.

How long after taking vitamins can I drink coffee?

It’s recommended to wait at least 30 minutes to an hour after taking iron supplements before drinking coffee. Coffee and tea contain compounds like polyphenols that can inhibit the absorption of certain vitamins, especially iron. For other vitamins like B12 or C, coffee should not significantly interfere, but spacing out supplements and beverages is best for optimal absorption.

What vitamins should you avoid taking at night?

Some vitamins, particularly B vitamins (such as B12 and B6), can cause energy boosts and may interfere with sleep if taken late at night. Vitamin D might also be best taken earlier in the day, as it supports energy levels. For better sleep, avoid high doses of magnesium or other calming supplements close to bedtime if you're sensitive to their effects.

Can I take vitamin C with other vitamins?

Yes, vitamin C can generally be taken with other vitamins, but high doses should be spaced out from Vitamin B12 supplements, as vitamin C can degrade B12 in the digestive tract. Otherwise, vitamin C works well with iron supplements, enhancing iron absorption.

Should I take vitamins on an empty stomach or with food?

Fat-soluble vitamins (like vitamin A, D, E, and K) should be taken with food to aid absorption. Water-soluble vitamins (like vitamin C and B vitamins) can typically be taken on an empty stomach, but taking them with food can reduce stomach irritation.

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This article is for informational purposes only and is not a substitute for medical advice. Consult your doctor or healthcare provider before starting any supplements, treatments, or remedies. Ensure a varied and balanced diet and a healthy lifestyle before considering supplements. Supplements should not replace a balanced diet.