Eating a variety of healthy foods is the best way to meet the majority of your nutrient needs, but if you’re low on a certain vitamin or mineral, or want to optimize your health with non-nutritive supplements (like green tea extract), knowing which supplements to take–and when– can maximize your benefit.
However, there are certain supplements that you shouldn’t take together. Here are some common ones to watch out for:
Iron + Calcium
When taken at the same time, iron and calcium bind together and significantly reduce absorption. Since iron is best absorbed when taken on an empty stomach and in the presence of vitamin C, it’s recommended to take it at least 2-3 hours before or after a calcium supplement.
Vitamin C + B12
Taking vitamin B12 with vitamin C may lower the amount of B12 available in your intestine. To avoid this interaction, wait 2-3 hours to take vitamin C after your B12 supplement.
Potassium, Calcium, Zinc, and Magnesium
Large doses of these mineral supplements can compete for absorption if taken at the same time and will not be as effective. If you take more than one mineral supplement, take them separately and at least two hours apart.
Multivitamin/mineral (MVM) + Calcium, Zinc, Magnesium, or Potassium
Single mineral supplements –including calcium, zinc, and magnesium –may interfere with the absorption of smaller minerals found in a multivitamin/mineral, like iron and zinc. For optimal absorption and maximum benefit, take your multivitamin a minimum of 2-3 hours before a calcium, zinc, magnesium, or potassium supplement.
Vitamins D, E + K
Some evidence suggests that moderate to large doses of the fat-soluble vitamins –specifically vitamins D, E, and K– may compete for and reduce absorption when taken together. The absorption of vitamin K seems to be most affected in the presence of other fat-soluble vitamins [1
]. Take these supplements at least two hours apart and with some sort of dietary fat to optimize absorption.
Copper + Zinc
Though rare, copper deficiency can result from high levels of zinc, which decreases the body’s ability to absorb and use copper from the diet. If you’re taking a daily zinc supplement, you should consider a copper supplement as well to avoid the potential for copper deficiency. However, don't take them at the same time; wait at least 2 hours after taking zinc to take your copper supplement.
Green tea contains a compound that binds to iron. When consumed together, green tea extract loses its antioxidant potential and iron absorption is severely reduced. To minimize this interference and maximize iron absorption, take green tea extract 2-3 hours before or after an iron-rich meal or iron supplement.
Multivitamins typically combine most (if not all) essential vitamins and minerals into one pill, so the absorption level of each nutrient is highly dependent on your own nutrient level, as well as the dose and form of each vitamin or micronutrient [4
]. Given this, multivitamins are a good safety net and can help prevent deficiency by filling nutrient gaps in the diet, but individual supplements are typically most effective for treating specific deficiencies.