Supplement and food interactions

Which supplements to take together, which to keep apart, and which foods get in the way. Every answer cites its source: the NIH Office of Dietary Supplements, Oregon State’s Linus Pauling Institute or a published study.

34 pairs · Updated October 10, 2026

Iron

• Can You Take Iron and Calcium Together?Possibly. Calcium might interfere with iron absorption, so experts suggest taking calcium and iron supplements at different times of day.
• Can You Take Iron and Zinc Together?Iron supplements of 25 mg or more taken at the same time as zinc supplements can lower zinc absorption and blood zinc.
• Do Coffee and Tea Block Iron Absorption?Coffee and tea can inhibit iron absorption: in a study in adults, coffee and tea drunk with a bread meal cut the iron absorbed from it.
• Do Iron and Copper Work Together?Yes. Copper takes part in iron metabolism, and anemia is one effect of copper deficiency, which is uncommon.
• Do Iron and Manganese Compete?They are linked: iron deficiency raises manganese absorption and can make manganese toxicity worse.
• Do Whole Grains and Beans Block Iron?Phytate in grains and beans lowers non-heme iron absorption, but in a typical western diet the effect matters little for most people’s iron status.
• Does Riboflavin (Vitamin B2) Help Iron?Riboflavin is needed to use iron, so check riboflavin sources such as dairy, eggs and fortified grains when iron is short.
• Does Soy Affect Iron Absorption?Soy protein lowers non-heme iron absorption, largely because of its phytate.
• Does Vitamin A Help Iron?Vitamin A is needed to mobilise iron, so if iron and vitamin A are both short, address both.
• Should You Take Iron With Vitamin C?Yes. Vitamin C eaten with non-heme iron, the iron in plant and fortified foods, raises how much is absorbed.

Caffeine and alcohol

• Does Alcohol Deplete B Vitamins?Yes. Chronic heavy drinking drains thiamin, so it is a reason to keep thiamin covered.
• Does Alcohol Deplete Magnesium?Magnesium deficiency is common in people with chronic alcoholism.
• Does Caffeine Affect Calcium Absorption?Slightly. Caffeine reduces calcium absorption to a small extent; low vitamin D status reduces it more.
• Does Caffeine Cancel Out Melatonin?Evening caffeine can delay the body’s own melatonin rhythm.
• Should You Take L-Theanine With Caffeine?In one trial, L-theanine with caffeine improved some attention and memory measures and alertness compared with placebo.

Vitamins A, D, E and K

• Do Vitamin C and Vitamin E Work Together?Yes. Vitamin C has been shown to regenerate vitamin E in the body.
• Do Vitamin D and Magnesium Work Together?Yes. Low blood magnesium causes resistance to some of vitamin D’s effects, so keep magnesium intake adequate.
• Should You Take Vitamin D With Calcium?Vitamin D is needed to absorb calcium, and bone needs both: low calcium and/or vitamin D contributes to osteoporosis.
• Should You Take Vitamin D With Food?It helps. Fat eaten at the same time enhances vitamin D absorption, though some is absorbed without it.
• Should You Take Vitamin E With Food?Yes. The digestive tract needs fat to absorb vitamin E.
• Should You Take Vitamin K With Food?Vitamin K is absorbed along with dietary fat, in the same micelles that fat digestion forms.

Zinc, magnesium and other minerals

• Can You Take Magnesium and Zinc Together?One study found very high zinc supplement doses, 142 mg a day, can interfere with magnesium absorption and magnesium balance.
• Do Choline and Folate Work Together?Yes. Both donate methyl groups, and when folate is low the body needs more choline.
• Do Folate and Vitamin B12 Work Together?B12 and folic acid are both linked to homocysteine: B12 helps turn homocysteine into methionine, and B12 and folic acid supplements both lower homocysteine.
• Do Iodine and Selenium Work Together?Selenium and iodine both matter for thyroid hormones; selenium deficiency could make iodine deficiency worse, and the adult upper limit for selenium is 400 mcg a day.
• Do Magnesium and Potassium Work Together?Yes. Magnesium helps move potassium across cell membranes, and severe magnesium deficiency can cause low potassium.
• Do Whole Grains and Beans Block Zinc?Phytate in grains and legumes lowers zinc absorption; soaking beans and grains before cooking and fermented foods may help, and animal zinc sources absorb better.
• Do You Need Black Pepper With Turmeric?In one study in healthy volunteers, 20 mg of piperine raised curcumin’s bioavailability about twenty-fold.
• Do You Need Copper With Zinc?Zinc at 50 mg a day or more for weeks can interfere with copper absorption and lower copper status.
• Does Licorice Lower Potassium?Yes. Regular, heavy licorice can lower potassium and raise blood pressure, so it is worth stopping if potassium runs low.
• Does Salt Affect Calcium?Yes. A high sodium intake increases the calcium lost in urine, so eating less sodium means less calcium lost.
• Does Tryptophan Turn Into Niacin?Yes. The body makes niacin from tryptophan: 60 mg of tryptophan counts as 1 mg of niacin.
• How Does Potassium Balance Sodium?Potassium may help counter sodium’s effect on blood pressure, so potassium-rich foods are worth having alongside eating less salt.
• Should You Take Collagen With Vitamin C?Vitamin C is needed to build collagen, so make sure you get enough of it.

General information from the cited sources, not medical advice. Interactions with prescription medications are not covered on these pages; ask a pharmacist.