Learn 10 surprising facts concerning your daily dose

Before you pop your next multivitamin or consider a new supplement, consider these 10 little-known facts:

1. Temperature

Refrigerate supplements that contain oils (such as fish oil or omega-3 fatty acids) or probiotics. “Heat, light and oxygen are the elements that make oils go rancid and kill probiotics,” says Rashmi Gulati, MD, medical director at Patients Medical in New York. “If your pills are exposed to any of these for long, they will be completely useless.”

2. Drug Interactions

If you take aspirin or are on birth control, you may need to boost your vitamin C intake. “People who frequently take moderate-to-large doses of aspirin lose vitamin C in the urine and may need higher doses to maintain their blood levels,” says Kathi J. Kemper, MD, author of Mental Health, Naturally: The Family Guide to Holistic Care for a Healthy Mind and Body. Contraceptives that contain estrogen can also lower C levels.

3. Synthetic vs. Natural

Go synthetic when it comes to folate, a type of B vitamin that’s especially important for women of childbearing age. Kerry Neville, RD, spokesperson for the American Dietetic Association, says that synthetic-based supplements are actually easier for the body to absorb than those made from natural sources.

4. B12 Benefits

You might want to consider taking a B12 supplement if you don’t eat much meat. Vitamin B12, an important vitamin that helps metabolize folate as well as protect the nervous system, is found mainly in animal products. “Vegans definitely need a B12 supplement because the kind found in some plant foods is in a form the body cannot use,” says Elisa Zied, RD, CDN and author of Nutrition at Your Fingertips.

5. Volume

Even though vitamins are good for you, more is not necessarily better. For example, “huge doses of vitamin C or magnesium can cause diarrhea,” says Dr. Kemper. Other vitamins pose even greater risk when overused, including vitamin A and niacin, which can cause liver damage and other issues.

6. Iron Awareness

If you’re using a multivitamin that contains iron, be sure to take only the suggested amount per day or week. Most people don’t need extra iron unless they’re pregnant, anemic or have a poor diet; if you ingest too much, it’s possible to overload your system, says Dr. Gulati. An excess of iron can be damaging—especially in men—to the liver, heart and pancreas.

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