Q: Should I be taking a multivitamin every day? What specific things should I look out for in my multi? ~Maria S, New York, NY

A: Great question, Maria! According to Dr. Paul Thomas, a Scientific Consultant for Office of Dietary Supplements of the National Institute of Health (NIH), multivitamins serve as “nutritional insurance.” Healthy individuals should obtain most of their nutrients from a balanced diet, but taking a multivitamin every day ensures that you are getting all the nutrients your body needs to function properly. While there is no conclusive proof that people taking multivitamins are healthier and live longer than those who do not, suggestive evidence of benefits is growing. For example, taking a multi for 15 years was linked to a 75% lower risk of colon cancer in a large group of female nurses.[1]

In terms of getting just the right amount, it is important to note that there is such a thing as taking too much vitamin. Vitamins A, D, E and K are the four fat-soluble vitamins, which means they can accumulate in the fatty tissues your liver and can amount to high concentrations if taken in excess. Small amounts of these vitamins are needed to maintain good health, but the body does not need these every day and will store them in the liver when not used. Megadoses of vitamins A, D, E or K can be toxic and lead to health problems.

Too much of a good thing?

Vitamin A: Most multis are too high in vitamin A. It is recommended not to take more than 5,000 IU of vitamin A unless it is in the form of beta-carotene (which your body converts to vitamin A).[2] Most multis supply vitamin A as retinol (eg, retinyl acetate or retinyl palmitate), beta carotene, or a combination of the two, but only retinol can build up to toxic levels.[3] If the label does not specify the source, contact the seller or assume it is mostly retinol. Personally, I take the “Ultimate Woman” multi from Vitamin Shoppe, with 5000 IU of vitamin A, 50% from beta-carotene. They also have a version for men. Signs of severe overuse over a short period of time include dizziness, blurred vision and slowed growth. Vitamin A toxicity also can cause severe birth defects and may increase the risk for hip fractures.[4] Almost all multis provide enough of the other fat-soluble vitamins for most people and well below the Upper Limits.

Folic Acid: Adequate folic acid (or folate, as found in foods), may lower the chances of breast and colon cancer, particularly in those who drink alcoholic beverages since alcohol can reduce the absorption of this nutrient and increase urinary excretion of it.[5] Although most multis supply 400 mcg of this nutrient, the 800 mcg supplied by top-name vitamin sellers is excessive and brings the user dangerously close to the Upper Limit of 1000 mcg for adults.

Too little?

Calcium and iron:  If you take a multivitamin for calcium or iron, you might want to consider taking an additional supplement to get your fair share. This is because calcium and iron bind to each other, and do not get effectively absorbed if taken simultaneously. In addition, calcium is required in much larger amounts compared to most nutrients (1000-1200 mcg for adults), which would easily turn a multi into a “horse pill.” Taking two or more multivitamins a day may put you over the limit for your fat-soluble vitamins, so it you might want to consider adding a separate calcium supplement, depending on your diet.

Others: Check to make sure your multi supplies vitamin C, vitamin E, thiamin, riboflavin, niacin, vitamin B6, chromium, copper, iodine, selenium and zinc, which it probably does.[6] It should also provide 50-100 mcg of vitamin K (most supply only 25 mcg); about 10-20 mg of niacin (but no more than 35 mg); and about 100-200 mg of magnesium (not more than 350 mg). Many multis oversupply you with these nutrients so watch out!

Bottom Line: No multi is ideal, there are always tradeoffs. Choose your multivitamin carefully… an article from the The Dietary Supplement newsletter suggests thinking of a multivitamin as a seat belt that doesn’t give you permission to drive recklessly. [7] Taking a multi does not make up for a lousy diet or lack of physical activity. If you eat well and follow a balanced diet, you will get most of the nutrients you need.