If you’re like most women, you use vitamins and supplements like insurance, trusting them to make up deficiencies when your eating habits are less than stellar. But can you really skip fruits and veggies for a fistful pills? No way, say experts at the Mayo Clinic. You don’t get the same benefit; vitamins aren’t food substitutes.

Extra vitamins and supplements can also interfere with certain healthcare conditions and treatments, FDA experts warn. And this is particularly true of cancer survivors, says Cornelia Ulrich, PhD, a researcher who published a survey on the supplement habits of cancer patients earlier this year in the Journal of Clinical Oncology. “While supplement use may be beneficial for some patients, such as those who cannot eat a balanced diet, research suggests that certain supplements may actually interfere with treatment or even accelerate cancer growth,” she warns.

“Some vitamins, such as folic acid, may be involved in cancer progression, while others, such as St. John’s Wort, can interfere with chemotherapy,” Ulrich says.

In fact as many as 64% to 81% of the 10 million cancer survivors in the U.S. right now use supplements with their medical treatment—and most aren’t discussing this with their healthcare providers, the survey showed.

Take vitamins and supplements sensibly and wisely. Why take additional vitamin C when research shows that practicing good hand-washing skills is actually more effective in boosting your immune system and preventing colds?

Follow the federal guidelines for daily recommended values and always tell your healthcare provider about any vitamins or supplements you’re taking to avoid dangerous interactions.

There are times when you will absolutely benefit from a multivitamin boost, particularly if you’re:

• Eating a strictly vegetarian diet without any supplements
• Consuming fewer than 1,600 calories a day
• Pregnant
• Experiencing heavy menstrual bleeding
• Post-menopause
• Managing a food allergy or disorder, such as a gluten allergy, that interferes with your ability to absorb nutrition from food
• Removing or restricting food groups in your daily diet, such as carbohydrates or dairy

• Buy a multivitamin that provides no more than 100% of the daily value (DV) of the leading vitamins and minerals.
• Avoid megadoses or supervitamins—remember, your food is also providing you with these same benefits, especially if you’re eating healthfully.
• Look for proof that the label is accurate and contains the vitamins you think you’re consuming. A USP label ensures that the supplement meets standards for strength and purity by the U.S. Pharmacopeia (USP).
• Take your vitamin around the same time each day and with food to maximize absorption.
• Use or toss by the expiration date, and store vitamins in a dark, cool cabinet to preserve freshness.