Most dietary supplements can be taken with or without foods, but sometimes taking them on an empty stomach causes heartburn or an upset stomach. If that happens, taking the supplements with food may alleviate the discomfort.
Foods and Absorption
Foods can change how you absorb certain nutrients -- sometimes that's good and sometimes that's bad. Calcium carbonate supplements require stomach acid, so they're best taken with meals. Another common form, called calcium citrate, doesn't need the extra acid so it can be taken on an empty stomach.
Iron absorption can be increased when you consume vitamin C at the same time. You can take vitamin C supplements or eat foods or beverages that contain large amounts of vitamin C (like orange juice, peppers or strawberries).
Milk or tea can interfere with iron absorption. This isn't a big deal if you're taking a little iron to ensure adequate intake, but if you're taking iron supplements to treat iron-deficiency anemia, you may need to be more careful. Follow the directions on the supplement package label or speak with your health care provider to make sure you're getting enough iron.
Dietary supplements can also include herbs and other natural substances that may affect absorption. Always speak with your health care provider about the dietary supplements you're taking, especially if you have any health conditions or if you're taking any medications.
United States Office of Dietary Supplements. "Dietary Supplement Fact Sheet: Iron." Accessed September 16, 2011. http://ods.od.nih.gov/factsheets/Iron-HealthProfessional
United States Office of Dietary Supplements. "Dietary Supplement Fact Sheet: Calcium." Accessed September 16, 2011. http://ods.od.nih.gov/factsheets/Calcium-QuickFacts/.