Three vitamin and supplement combinations you should AVOID

By: Gina Jaeger, PhD


  • For maximal iron absorption, avoid pairing sources of iron with foods or supplements high in calcium
  • High doses of zinc (often found in supplements for immune health) can inhibit the synthesis and absorption of the essential mineral, copper
  • Although still under investigation, research suggests that taking large doses of vitamin A can impede dietary vitamin D absorption

Optimal health is top of mind these days, and it’s not hard to see why. As people around the world look for nutrient-based ways to support their immune health, an important consideration is how the vitamins and minerals they are consuming work together towards greater foundational health.

Not all supplements should be taken together as they can affect how the other is absorbed.

Although taking a “more is merrier” approach to nutrient consumption might seem like a smart way to stay healthy, the truth is, too much of a good thing (especially in combination with too much of another good thing) can actually be a bad thing.

In this article, we’ll review some of the most important nutrient interactions to be mindful of.


Because vitamins and minerals interact at a chemical, biochemical, or physiological level, taking large doses of individual nutrients can impact how the body absorbs and utilizes other nutrients.

In some cases, these nutrient-nutrient interactions can be a positive thing, with the nutrients enhancing each other’s absorption or function. In other instances, however, high doses of specific nutrients can impede the body’s absorption or utilization of other nutrients—leading to issues of malabsorption, deficiency, or even suboptimal health outcomes. In other words, exactly the opposite effect you were going for.

For those of you now thinking about your next meal with apprehension, relax. The great thing about getting your nutrients from whole foods is that Mother Nature tends to package nutrients that complement each other together in individual foods.

Also, because we tend to consume a greater variety of nutrients at smaller doses from food sources than supplements, there is less opportunity for large doses of certain nutrients to impede the absorption of others.

This is not to say that nutritional supplements are not without their purpose or advantages. For many people, supplements offer the most feasible way to ensure vital nutritional requirements are continually satisfied.

What’s more, because it can be difficult to consume adequate amounts of certain nutrients from dietary sources alone (e.g., vitamin D), supplements can provide the means to overcome a deficiency quickly. However, because supplements can be taken in larger doses, it’s important to know how individual nutrients influence other’s effects on the body.

  • Iron x Calcium
  • Zinc x Copper
  • Vitamin A x Vitamin D


If you’re looking for ways to increase your iron intake, combining iron-rich foods or supplements with calcium is not the way to go. This is because calcium can inhibit the absorption of iron in both food and supplement form.

Rather than cutting out calcium, the best way to optimize your iron absorption is to consume these essential nutrients at different times.

Rather than pairing a spinach salad with a hearty serving of cheese or glass of milk, try to consume these important nutrients separately.

For example, consider eating a breakfast high in calcium (e.g. yogurt, cottage cheese, calcium-fortified cereal) and a lunch or dinner high in iron (e.g., spinach, lentils, red meat, fish, and poultry).

The same goes for supplements. If your daily health regimen includes both an iron and calcium supplement, be sure to take them at different times of the day to achieve the best results.

Given that iron supplements can sometimes lead to gastrointestinal discomfort, our recommendation is to take your calcium supplement earlier in the day, and your iron supplement at night.

Another reason to consume these nutrients at separate times is that high amounts of iron and calcium together can lead to reduced levels of zinc—another essential mineral which we’ll talk about next.


Zinc and copper are essential trace minerals that contribute to vital physiological processes, including immune functions. For instance, zinc promotes immune cell development and has been found to positively influence the outcome of certain viral complications.

Although the exact mechanisms through which copper supports immune health are not well defined, numerous studies indicate a strong correlation between copper deficiency and suboptimal immune health.

For these reasons (and more), zinc and copper are commonly found in multivitamins offering to support immune health.

Despite their individual health benefits, taking high doses of zinc is not encouraged. This is because zinc exerts an antagonistic effect on copper, which effectively inhibits its absorption, leading to copper deficiency.

In addition to the suboptimal health outcomes associated with copper deficiency, research shows that a high zinc to copper ratio can lead to increases in oxidative stress, immune dysfunction, and inflammation.

In order to lessen the chances of zinc impeding copper absorption, a good rule of thumb is to take supplements containing zinc and copper a few hours apart.

Obviously, this is impossible if you are taking a multivitamin that includes both minerals; however, we suggest avoiding any supplements or multivitamins that provide doses of zinc higher than 40 mg/day (unless instructed by a medical professional), as this will likely interfere with copper absorption.


Vitamins A and D are integral to human health and serve diverse bodily functions. Although necessary for eye health, immune function, and healthy embryonic development, research finds that consuming doses of vitamin A (retinol) larger than 10,000 IU/day or 3000 mcg/day (for adults) can result in toxicity and other sub-optimal outcomes.

For this reason, taking more than the recommended amount of vitamin A or combining supplements containing vitamin A is often discouraged, especially for pregnant women. (Keep in mind that that term “vitamin A” can refer to retinol (preformed vitamin A) or certain carotenoids (provitamin A) which are converted by the body into vitamin A. Whereas retinol presents a vitamin A toxicity risk, carotenoids do not).

Another important consideration is how vitamin A interacts with vitamin D which is often called the “sunshine vitamin” because of the body’s ability to synthesize it from sunlight.

Amongst other health benefits, vitamin D3 (cholecalciferol) supports immune function, promotes the formation of healthy bones, and supports calcium absorption.

Notably, several studies indicate that high levels of vitamin A can act as an antagonist for vitamin D absorption, and actually decrease the body’s uptake of vitamin D by 30%.

Interestingly, vitamin A also appears to discriminate between different sources of vitamin D.24 More specifically, one study showed that vitamin A negatively affected the utilization of dietary Vitamin D3, but not vitamin D from the sun.

The exact mechanisms through which vitamin A inhibits vitamin D absorption remain unclear and requires further investigation.

All the same, individuals with potential vitamin D deficiencies (older adults, people with limited sun exposure, people with darker skin pigmentation, etc.) should be mindful of their vitamin A consumption and take vitamin A and D supplements (if indicated) at least a few hours apart.


Consuming the essential nutrients, you need for optimal immune functioning and foundational health is important year-round, but especially important in light of today’s current health crisis.

Thus, it is imperative that you don’t “undo” any of your good dietary intentions by combining nutrients that can impede each other’s function. We encourage you to speak with your health professional about your daily diet or supplement regimen to further ensure you’re optimizing nutrient absorption.



Further reading: Find out which vitamins and minerals you can (and should) take together.


About the author

Gina Jaeger, PhD is a Developmental Specialist and Lead Research Writer for Nordic Naturals. She holds a doctorate in Human Development, and has published several research articles on children's cognitive development. Gina enjoys studying and educating others on strategies for optimizing health and wellness throughout the lifespan.

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