Vitamin C

The recommended daily amount of vitamin C for adult males? Just 90 milligrams (mg). For some perspective, there are almost 70 mg in one medium-sized orange. And, according to the National Institutes of Health (NIH), vitamin C deficiencies are rare in the United States.

Yet C supplements typically come in doses of 500 and even 1,000 mg. People often take vitamin C to prevent cardiovascular disease and the common cold. (It hasn’t been proven to stave off sickness, but it has consistently been found to reduce the duration of cold symptoms.)

It might sound like a magical vitamin, but “supplementing with vitamin C beyond your typical needs hasn’t been shown to provide any real benefit,” says Roussell. “It generally doesn’t do any harm unless you take grams at a time—and then you can get diarrhea.”

Magnesium Oxide 

Magnesium is a very important mineral that is involved in more than 300 reactions in the body, impacting important factors like blood sugar control and muscle contractions. The key issue with magnesiumsupplements comes down to one thing: absorption.

“Magnesium oxide contains the most magnesium per gram compared to other magnesium supplements,” says Roussell. “However, it is absorbed the poorest.”

Most American diets provide less than the recommended amounts of magnesium (400 to 420 mg), according to the NIH, so a supplement isn’t the worst idea. Just avoid the bottles with magnesium oxide on the label.

Instead, opt for a chelated magnesium, where the minerals have been chemically combined with amino acids. This way, minerals are more likely to survive the passage from your stomach to your small intestines intact—leading to greater absorption.

Roussell says to look for labels marked magnesium-glycinate, -fumarate, -taurate or –orotate.

B-Complex Vitamins 

The eight B vitamins—B1, B2, B3, B5, B6, B7, B9 and B12—are known collectively as B-complex vitamins. These have been proven to help your body convert food into fuel for energy, maintain metabolism, keep your mind sharp, promote healthy skin and hair, and more.

A super pill loaded with all eight vitamins seems like a no-brainer, but Roussell says it’s simply not necessary.

“B-vitamins are very ubiquitous in fruits, vegetables, nuts and grains,” he says. “They are everywhere and there are no documented benefits of taking additional B-vitamins in healthy individuals.”

It’s not just supplement companies looking to cash in on vitamin B’s good name, either: “B-complex vitamins are touted in countless energy drinks for their ability to help boost energy.” The reality: “They don’t,” says Roussell.