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Grocery aisles are full of supplements claiming to do everything from preventing you from getting a cold to improving your mood and reducing stress. These potential benefits have made supplements much more popular over the years, with some people taking more than a handful each day. However, taking certain supplements together can cause more issues than benefits. They may counteract each other, one may hinder absorption of the other, or they may lead to undesirable health effects when taken in combination. Here are 7 supplement combinations you should not take together or be careful about combining.
1. Zinc and Calcium
“Zinc and calcium compete for absorption in the gut, so taking them together can limit the effectiveness of both,” says Alyssa Simpson RDN, CGN, CLT, digestive health dietitian. Zinc is often used to support your immune health or wound healing, and calcium is used to fill dietary gaps that could harm your bone health. Yet, they probably won’t have these desired benefits if your body can’t absorb them well. To avoid this, Simpson recommends taking zinc and calcium supplements at least two hours apart.
2. Iron and Zinc
“Iron can reduce the absorption of zinc, and zinc may lower the absorption of iron when these supplements are taken together,” says Elizabeth Harris, M.S., RDN.
In particular, iron supplements with 25 mg of iron or more could be problematic for zinc levels. Although high doses of iron are very common when treating iron deficiency, they can reduce zinc absorption and total plasma zinc concentrations. To avoid this, taking a zinc and iron supplement at least two hours apart is best.
3. Iron and Calcium
“Calcium inhibits the absorption of non-heme iron (the type of iron found in supplements and plant-based sources) by competing for absorption in the intestines,” says Carla Hernandez RDN, a registered dietitian. This effect isn’t 100% definitive, but research does show it’s likely. This could be problematic if you’re trying to correct iron deficiency. So, to be safe, Hernandez recommends taking calcium and iron supplements at least two hours apart to ensure adequate absorption.
4. Magnesium and Zinc
“Magnesium and zinc compete for absorption in the intestines, meaning taking high doses of both at the same time can reduce how much your body absorbs each mineral,” says Hernandez. This is particularly true for very high doses of zinc (upwards of 140 mg per day), which far exceeds the tolerable upper intake level of 40 mg for adults. Still, your healthcare provider may advise that you space these two supplements out just in case.
“Take magnesium and zinc supplements at different times of the day, such as magnesium in the evening and zinc in the morning. I recommend taking zinc with food as it has a tendency to cause nausea,” recommends Hernandez. And since magnesium glycinate (a type of magnesium) can help support relaxation and sleep, it’s a great option to take at night.
5. St. John’s Wort and Serotonergic Supplements
St. John’s wort is a herbal supplement often used to help manage depression, although research is still mixed on its efficacy. That said, it may raise serotonin levels, so you should not take it in combination with anti-depressant medications, as this could lead to a life-threatening increase in serotonin levels.
There are also risks of taking St. John’s wort with serotonin-boosting supplements. “Combining St. John’s Wort with serotonin-boosting supplements like 5-HTP or SAMe can elevate serotonin levels too much, potentially leading to symptoms like restlessness and confusion,” says Simpson. The solution? “Stick to one serotonin-supporting supplement at a time.” Before starting any of these supplements, we suggest speaking with your healthcare provider for individualized guidance.
6. Ginkgo Biloba and High-Dose Fish Oil
“Both ginkgo biloba and high-dose fish oil thin the blood, and when combined, they can increase the risk of excessive bleeding,” says Simpson. This is especially true if you’re also taking a blood-thinning medication like warfarin, says Angie Konegni M.S., RD, CSR, LD.
Other potentially blood-thinning supplements to be careful about taking together are aloe, garlic, ginger, turmeric, fenugreek and ginseng, among others. If you’re taking any of these supplements in combination, “consider alternating or lowering the doses to avoid stacking their effects,” recommends Simpson.
7. St. John’s Wort and Ginseng
As mentioned above, St. John’s wort may help counter depression by raising serotonin levels. Turns out ginseng may have similar effects. So, taking the two together could cause issues. “Both are known to affect mood and energy levels, but combining them may overstimulate the central nervous system, leading to symptoms like agitation, rapid heart rate, or even serotonin syndrome, a potentially life-threatening condition,” says Konegni.
What to Consider If You Take These Supplements
If you’re taking any of the above supplements, speak with your healthcare provider before adding a new one to avoid harmful interactions. If you’ve already been taking a supplement combination that could be harmful or hinder proper absorption, reach out to your healthcare provider so they can advise you on how to proceed. They may simply recommend that you start taking them a few hours apart.
Also, keep in mind that it’s more likely that you’ll encounter issues if you’re taking high-dose supplements. A healthcare provider can advise you on the appropriate dosage for meeting your nutrient or health needs without going overboard and increasing the risk of adverse effects.
How to Know What Supplement Combinations Are Safe
Before starting a new supplement, it’s best to speak with a healthcare provider to ensure it’s safe for you and guidance on an appropriate dosage. Make sure to share all the supplements and medications you’re taking so your healthcare provider can let you know whether there are any supplement or drug interactions to be aware of. This is the best way to ensure your unique combination of supplements is safe to take.
The Bottom Line
Whenever possible, prioritize food over supplements. Food-food interactions are much less common, and foods contain a whole host of beneficial nutrients that work together to support your health. If you need to take any of the above supplements, speak with a healthcare provider for individualized guidance so you don’t accidentally pair supplements that can interact with one another.