Multivitamins are the most commonly taken supplement. Here’s what they can (and can’t) do for your health

About one-third of Americans rely on this versatile tablet to fill the nutritional gaps in their diets. · Fortune · Getty Images

If you’re trying to cover all your nutritional bases in one pill, you may think multivitamins are the obvious solution. About one-third of Americans rely on this versatile tablet to fill the nutritional gaps in their diets, but before you join the flock, it’s worth learning about everything multivitamins can and can’t do.

Ahead, dietitians tell Fortune whether these multitasking supplements are worth their weight in nutritional benefits—or whether you’d be better off spending your dollars elsewhere.

The benefits of taking multivitamins

Most multivitamins contain vitamins A, D, E, K, C, B, calcium, magnesium, iron, zinc, selenium, manganese, and chromium, explains Jamie Lee McIntyre, RD. That means that a multivitamin offers all the benefits associated with those nutrients. For example, vitamin C can help boost your immune system, vitamin B may improve brain function, and calcium may help your body maintain strong bones.

Their nutritional breadth makes multivitamins a great “insurance policy” for your health and well-being. “While individual nutritional needs vary from person to person depending on age, sex, health status, and lifestyle, many multivitamin supplements provide nutrients that play crucial roles in various physiological processes to prevent deficiencies that would otherwise cause health problems,” says McIntyre.

Of course, multivitamins are also convenient. Rather than taking a myriad of pills in the morning, you can pop one (often large) tablet at breakfast and call it a day.

Where multivitamins fall short

While multivitamins are multifunctional, they’re not a panacea. “Multivitamins are not a replacement for a well-balanced diet,” says McIntyre. “Research shows that most nutrients are best absorbed from foods. Researchers believe this is due to synergistic effects that occur when nutrients like vitamins, minerals, and antioxidants are consumed, digested, and metabolized from food sources.”

Our bodies have evolved to collect nutrients from whole foods. While we can get them from vitamins, too, it’s not nearly as effective as just, well, eating. “Digestion and absorption starts when we actually look at food,” says sports dietitian Leron Sarig, RD, nutrition specialist manager at Exos. From there, we chew, swallow, and soak up the nutrients we’ve just consumed.

Eating whole foods instead of vitamins also allows you to reap the other benefits of a given ingredient. For example, rather than getting pure vitamin C, you’re getting all the nutrients that come from eating, say, an avocado. “Especially when it comes to fruits and vegetables, the fiber that you get from them is from part of the fruit or vegetable that’s not necessarily getting powdered up and put in a multivitamin,” says Sarig.