What Vitamins Should Not Be Taken Together?

It might seem like taking a vitamin or mineral supplement could only be beneficial. After all, from a very young age, our parents impress the importance of getting enough nutrients in order to grow up healthy and strong.

While taking a dietary supplement is beneficial for many people, there are some vitamins that should not be taken together and some medical conditions in which people should avoid taking certain vitamins or minerals. To make sure that your dietary supplement isn’t doing more harm than good, we have put together a list of what vitamins should not be taken together as a result of potential interactions with other nutrients or medical conditions.

Calcium and Vitamin D

You’ve probably heard about the importance of calcium and vitamin D in promoting strong bones and teeth. Calcium is an important mineral that also supports heart health. Approximately 40 percent of the population in the United States is deficient in vitamin D, which plays a major role in calcium absorption. Without an adequate supply of vitamin D, your body cannot properly absorb and use calcium. 

While the two substances work in tandem, taking them together may not be such a good idea. A study conducted in July 2019 found that when taken together, calcium and vitamin D can cause a slightly increased risk of stroke. The long term study analyzed results from 160,000 women, but the findings are not without controversy. Another article did not find a correlation between taking calcium and vitamin D together and an increased risk of stroke. A separate study showed that it may be calcium supplements that cause the increased risk of stroke, while taking them in combination with vitamin D appeared to diminish this risk. Clearly, the jury is still out on whether or not taking calcium and vitamin D together can increase your risk of experiencing a stroke. Prior to taking the two supplements together, talk to your doctor to make sure that the benefits outweigh the risks. 

Calcium and Iron

Calcium and iron are two important minerals that the body needs in order to function properly. Iron is critical for the production of red blood cells, while calcium is essential for strong bones and teeth and a healthy heart. People who are deficient in iron can experience a condition called iron-deficiency anemia, the symptoms of which commonly include extreme fatigue, weakness, and lethargy. Normally, increasing your consumption of iron-rich foods, such as beef, dark leafy greens, lentils, beans, and dried fruit is enough to improve your iron levels, but some people may also need to take an iron supplement. However, people who take calcium supplements need to be aware of the timing of taking their supplements. The National Institutes of Health found that the body may not be able to effectively absorb iron when an iron supplement is taken in combination with a calcium supplement. To avoid this issue, it is recommended that people taking both supplements take them several hours apart. 

Niacin and Cholesterol Medications

Vitamin B3, also referred to as niacin, is generally considered a safe supplement to take in combination with other vitamins and minerals, and many multivitamins include vitamin B3. Vitamin B3 is often recommended for use with cholesterol medications, especially simvastatin, to help increase your levels of high density lipoprotein (HDL), or “good” cholesterol. However, the combination of niacin and cholesterol medications with other vitamins may have unintended effects. Using a supplement for vitamin C, vitamin E, or beta carotene may negatively impact the ability of niacin and your cholesterol medication to increase your HDL levels. More research is needed on this topic, as the interaction has only been observed in patients who have a current diagnosis of coronary artery disease. However, if you take cholesterol medication and a multivitamin, talk to your doctor about how to benefit most from your medication.

Folate and Vitamin B12 Deficiency

Vitamin B12 and folate, or vitamin B9, are two essential vitamins that must be acquired through diet or supplementation because the body cannot produce them naturally. Vitamin B12 deficiency is quite common, particularly in people who follow plant-based diets, such as vegans and vegetarians, because most of the best sources of vitamin B12 come from animal products. People with certain gastrointestinal disorders or those who have had weight loss surgery are also considered more at risk of vitamin B12 deficiency. Folate is especially important during pregnancy, during which time women need higher levels of folate in order to prevent significant birth defects from occurring. Although vitamin B12 and folate do not interact in a negative way when taken together, folate can mask a deficiency of vitamin B12.

Vitamin B12 deficiency can be serious and can cause a condition called megaloblastic anemia. When patients have this type of anemia, the red blood cells become unusually large but are lower in number. Folate can address the anemia, which makes people believe that they will not suffer any ill effects from their vitamin B12 deficiency. However, failure to address the vitamin B12 deficiency can cause permanent nerve damage. Therefore, patients who are considered at risk of experiencing a vitamin B12 deficiency, including older adults, should talk to their doctor about supplementing their levels of vitamin B12 and should take care to avoid ingesting too much folate. The maximum recommended daily amount of folate is 1,000 mcg from food and supplements unless otherwise directed.

Vitamins K and E and Blood Clotting

Vitamin K is very important in supporting the body’s ability to properly clot the blood. People who have a deficiency in vitamin K may have difficulty with getting their blood to clot properly and quickly and are considered at risk of bleeding. Patients whose doctors have advised them to take vitamin K should avoid taking high doses of vitamin E, particularly in the form of a supplement. Vitamin E has been found to counteract the effects of vitamin K, and when taken in especially high doses, vitamin E can make your blood thinner and affect the body’s ability to properly clot the blood. Patients taking blood thinning medications, such as warfarin, Xarelto, or Eliquiis, should be especially cautious about their vitamin E intake, as taking these medications and vitamin E can increase your risk of bleeding. As a general rule, patients taking blood thinning medications should speak to their physicians before taking any vitamin or mineral supplement.

Vitamin A and Pregnancy or Retinoids

Vitamin A is a fat-soluble vitamin, which means that the body can store the vitamin when it is consumed in excess quantities. Vitamin A plays many different roles in maintaining the health of the body, including supporting eye health, and while it is extremely important, it can also be dangerous and cause significant side effects when received in very large amounts. Most people receive enough vitamin A through their diets, as it is found in many different foods, so supplementation is generally not necessary. Pregnant women who receive too much vitamin A may experience serious birth defects, so it is recommended that women of childbearing age avoid taking multivitamins or other supplements that contain vitamin A. It is easy to take in too much vitamin A given its availability in so many plant- and animal-based foods, so women who are able to become pregnant should steer clear of supplements that include it.

Additionally, certain medications, such as retinoids, are composed largely of vitamin A. Accutane is a medication made up of a very high dose of vitamin A that is used to treat severe acne. Patients using retinoids and certain other medications must not take supplements that contain vitamin A and should watch their intake of vitamin A, as receiving the vitamin in large quantities can cause very serious side effects and complications.  Make sure to talk to your doctor about what supplements are safe when taking these medications, and always check with your healthcare provider before starting a new dietary supplement.


Multivitamins seem like just about the healthiest choice that you could make, given that the importance of getting enough vitamins and minerals is impressed upon us from a very young age. However, not all dietary supplements are created equally, and the nutrients each multivitamin contains can vary widely, as can the dosage of the nutrients. When considering taking a multivitamin, patients should look for a dietary supplement that provides no more than 100 percent of the daily value of each nutrient. Most people receive at least some of each vitamin and mineral from their diet, so taking extremely high doses of vitamins and minerals can be dangerous if you also have a large dietary intake. There may be some situations in which your doctor prescribes a dosage higher than the daily value of a particular vitamin or mineral, usually as the result of a deficiency. If this is the case, make sure to talk to your healthcare provider about other dietary supplements or herbal supplements you are taking in order to avoid a potentially serious interaction.