A Health Expert Shares 3 ‘Dangerous’ Vitamin Combinations That ‘Should Be Avoided’: Calcium And Magnesium, More

1. Calcium and Magnesium

Calcium and magnesium are two common supplements. Although they're both undeniably crucial nutrients for muscle, nerve, and bone health, Dr. Bowring explains that they’re better taken separately.

"These two vitamins in the same supplement is not a good idea because they compete for absorption," she says. "Did you know that magnesium is a natural calcium channel blocker? So if you take them at the same time, you’re not going to maximize the absorption of either." In short, these minerals can interfere with each other’s effectiveness, meaning your body may not be getting the full benefits of either nutrient. Good to know!

2. Vitamin D and Vitamin K

Although Vitamin D and Vitamin K are a common pairing for bone health thanks to the fact that they support calcium metabolism, Dr. Bowring cautions against taking them at the same time.

"And why is that? Well, we don’t want to cause something called hypercalcemia—too much calcium in the blood," she explains. "That can happen when you take these two nutrients together." Hypercalcemia can lead to symptoms like nausea, fatigue, kidney issues, and even abnormal heart rhythms—so this is one combo to approach with extra care and guidance from a health professional.

3. Any Vitamin + Magnesium Stearate

Finally, Dr. Bowring warns against a common ingredient in supplements: magnesium stearate.

"If you are taking a multivitamin, maybe you’re taking vitamin A, vitamin E, vitamin C—if it’s got magnesium stearate in there, that is a flow agent, it’s not a natural ingredient, and it should be avoided," she says.

Although magnesium stearate is generally safe in moderation, excessive supplementation could affect nutrient absorption—so it's best to proceed with caution. When in doubt, talk to your doctor!