Dangerous duos: 5 supplement combos to avoid

Let’s face it: Many of us don’t follow the best diets. As a result, our bodies may be lacking in certain essential vitamins and minerals. The good news is that, overall, most Americans are getting enough of some important nutrients—like folate, vitamin D, and iodine—according to the CDC. The bad news? Many of us aren’t getting enough of all the major vitamins and minerals our bodies need. For instance, according to the most recent US Dietary Guidelines, a number of Americans aren’t getting sufficient amounts of dietary fiber, potassium, choline, magnesium, calcium, iron, and vitamins, A, D, E, and C. So, what do we do when we have one or more nutritional deficiencies? We either tweak our food choices or take supplements to fill these gaps. In fact, 86% of Americans take vitamins or supplements, according to a poll conducted on behalf of the American Osteopathic Association. But, if you have more than one nutritional deficiency—or are already taking supplements to support another key area of health—can you save yourself some time by taking your meds all at once?

You can—but it’s probably not a good idea. For some supplements, optimal absorption can depend on the time of day taken. Not only that—taking certain vitamins, minerals, or other supplements together can also reduce absorption and may result in adverse interactions, which can be harmful to your health. Let’s take a look at five supplement combos you should avoid.

Multivitamins

But, before we get to that, we need to address the elephant in the room: multivitamins. If certain nutrients can adversely interact with one another, then how or why are multivitamins even on the market? The answer isn’t so cut and dried. Most multivitamins are formulated in such a way to counteract any potential negative nutrient-nutrient interactions. They contain the appropriate levels of both synergistic and antagonistic nutrients, meaning that some vitamins and minerals can enhance or inhibit others. 

For example, researchers have shown that magnesium can improve vitamin D levels. On the other hand, vitamin A can decrease vitamin D uptake. That’s why you’ll almost always find that the percentage daily value (% DV) of vitamin D is higher than vitamin A on most multivitamin nutrition labels. 

The downside to this is that you could be getting too much or too little of a certain vitamin or mineral. If you’re deficient in vitamin A, for instance, taking a multivitamin might not fill your nutritional gap. On the flip side, excess levels of fat-soluble vitamins A, D, E, and K—obtained from food and/or supplements—can build up in your body and become toxic, causing serious health problems. 

Another drawback to multivitamins? Two important nutrients are generally either not included or included in very little amounts (≤ 250 mg): calcium and magnesium. They are considered macronutrients because we need to obtain them in large quantities. The daily requirements of calcium for men and women aged 51-70 years are 1,000 mg and 1,200 mg, respectively. For men and women of the same age group, the daily requirements for magnesium are 420 mg and 320 mg, respectively. (Compare these recommended intake values with those of the micronutrient selenium, which is 55 mcg for both men and women aged ≥ 51 years.)

So why are calcium and magnesium excluded or, at the very least, included in negligible amounts? Broadly speaking, large doses of some minerals (including calcium and magnesium) will compete with other minerals for absorption in the body.  

For these reasons, single vitamin or mineral supplements tailored to support individual health goals or to address nutrient deficiencies may be preferred over multivitamins. But, for the same reasons mentioned above, here are five supplement combos you should steer clear of, making sure to take them individually at least a couple hours apart:

Calcium and magnesium 

Calcium and magnesium work hand-in-hand to support bone health and other bodily functions. Magnesium is needed for calcium absorption. Because magnesium suppresses parathyroid hormone and stimulates calcitonin, it helps deposit calcium into our bones, preventing osteoporosis. Without magnesium, calcium would become toxic, depositing itself in soft tissue, which can lead to arthritis. So, you’d think that these two minerals should be taken together, right? As discussed earlier, however, taking large amounts of minerals with other minerals will reduce absorption. To maximize your calcium and magnesium supplement benefits, aim to take them at least 2 hours apart. 

Copper and zinc

Both copper and zinc are imperative for optimal immune health, including internal and external healing. They work closely together to improve wound elasticity and resistance. But, zinc can interfere with copper absorption. Furthermore, high supplemental doses of zinc (≥ 50 mg/d) over the long term can cause copper deficiency. Although uncommon, copper deficiency can lead to anemia, hypopigmentation, hypercholesterolemia, connective tissue disorders, osteoporosis and other bone defects, abnormal lipid metabolism, ataxia, and higher risk of infection. 

Fish oil and Ginkgo biloba

Omega-3 fish oil supplements don’t just offer heart-health benefits—they can also help with body weight and fat reduction, vision loss, and neurocognitive injury. Ginkgo biloba supplements, on the other hand, have been used for the treatment of cognitive impairment (though evidence on the efficacy of such has been mixed). What do these two supplements have in common? They both possess blood-thinning potential. Thus, taking them together can reduce or prevent blood clotting and potentially increase the risk of uncontrolled bleeding. 

Iron and green tea

Iron is another key player when it comes to immune health. This element facilitates oxygen transport, hemoglobin formation, the breakdown of free radicals, and mitochondrial respiration among other processes. If you mix it with certain beverages, however, your body won’t absorb the mineral. While a glass of orange juice can help boost iron’s absorption, thanks to vitamin C, a glass of milk can have the opposite effect due to calcium’s interference. 

Another antagonist? Green tea. Although the beverage may have many wonderful health benefits, enhancing iron’s bioavailability is not one of them. Researchers have shown that green tea can lead to iron deficiency anemia when consumed in large quantities. Likewise, iron has a negative impact on green tea’s efficacy. In a study led by Penn State researchers, drinking green tea after an iron-rich meal was shown to reduce green tea’s health benefits. 

Melatonin and St. John’s Wort

Extracts from St. John’s Wort have been used for centuries as an analgesic agent, a sedative, and a treatment for menopausal symptoms, anxiety, and depression. St. John’s Wort has also been reported to enhance both the therapeutic and adverse effects of herbs or supplements with sedative properties when used concomitantly. Because melatonin is a well-known, potent natural sleep aid, it’s best to avoid taking it in combination with St. John’s Wort. 

Plan A

Although supplements can, indeed, help address nutritional deficiencies, researchers have shown that food-sourced nutrients surpass their supplement-based counterparts when it comes to health benefits. Why? Simply put, the biologically active compounds found in these foods cannot be completely captured in a neat little pill. So, when addressing any nutritional gap, always aim to make your diet plan A.