Timing is everything when it comes to taking certain supplements. Taking some supplements too close together can affect absorption or potentially cause side effects. For instance, calcium can interfere with the absorption of iron, so these two should not be taken together. Similarly, high doses of vitamin E can alter the effectiveness of vitamin K.

Calcium carbonate is a common ingredient in treatments for stomach acid, according to BBC Science Focus, but it can cause problems for iron supplements, says Dr. Edward Saltzman, associated professor of medicine at Tufts University. Iron supplements need stomach acid to be properly absorbed, so taking them with an antacid defeats the purpose.

Zinc and copper supplements should not be taken together. “Zinc supplements may outright impair the absorption of copper,” says Saltzman. “Because of this, both zinc and copper supplements shouldn’t be taken at the same time.

Vitamin B12 (cobalamin) plays an essential role in red blood cell formation, cell metabolism, nerve function and the production of DNA, the molecules inside cells that carry genetic information, says the Mayo Clinic. People who follow a vegetarian or vegan diet might be prone to deficiency because plant foods don't contain vitamin B12. Older adults and people with digestive tract conditions that affect absorption of nutrients also are susceptible to vitamin B-12 deficiency. Taking vitamin B12 with vitamin C might reduce the available amount of vitamin B12 in your body. To avoid this interaction, take vitamin C two or more hours after taking a vitamin B12 supplement.

Vitamin E is a nutrient that's important for vision, fighting off diseases and the health of the blood, brain, and skin. Vitamin E is an antioxidant that protects cells from the effects of free radicals, which are unstable that can damage DNA. Taking vitamin E with vitamin K might keep vitamin K from working as it should. Vitamin K is crucial for blood clotting and bone health. It helps the body produce proteins necessary for these functions.

“Drug-nutrient combinations can influence absorption, metabolism, or excretion. It’s always a good idea to consult a reliable source when taking multiple vitamins and supplements to see how they’ll mix,” says Saltzman.