New studies suggest low levels of certain vitamins and minerals may be slowing you down.

By Rachael Schultz
January 30, 2018
Photo: Alliance / Shutterstock

You know not eating well or logging enough sleep can hurt your workout, but there might be something else slowing you down: A new study in the Journal of the International Society of Sports Nutrition found that when healthy, active, females supplemented with a specific vitamin and mineral formula for one month, they shaved about one minute off their 3-mile run, were able to bike farther in 25 minutes, and covered more steps in a 90-second time trial.

What's more, they performed these tests back-to-back with minimal rest in between, so the bump of nutrients helped improve their speed continuously over the nearly hour-long cardio workout.

Sounds pretty great, right? This magic formula was actually filled with pretty basic minerals: iron, copper, and zinc-three nutrients a lot of women are moderately deficient in, says study author Robert DiSilvestro, Ph.D., professor of human nutrition at The Ohio State University. (Related: 5 Minerals That Seriously Supercharge Your Workouts)

"A lot of supplements don't include iron, and if they have zinc and copper, they are often not added in the best forms," he says. DiSilvestro's team actually compared two different forms of iron, copper, and zinc, as well as a placebo, and found the type that might come in a multivitamin-gluconates-didn't boost performance as well as a variety called glycinates. Our body seems to absorb the glycinate form of these three minerals best, improving blood levels of the minerals most efficiently, DiSilvestro adds.

The superior supplement in the study also included two other amino acids, carnitine and phosphatidylserine, which are also not often supplemented by active young women and can help absorption of the three minerals, he adds. (Related: Your Guide to Pre- and Post-Workout Supplements)

But what's so special about these nutrients? "Think of energy production like a giant wheel that needs to be continually turned by a variety of different workers (nutrients). If one is out of position, it will slow things down. If everyone is at their correct positions, then the wheel can turn efficiently," says LA-based nutritional biochemist and sports dietitian, Jeff Rothschild, R.D., C.S.C.S.

And the fact that the supplement group saw a sustained benefit across the hour of exercise makes DiSilvestro hopeful that boosting these nutrients may improve performance across a variety of distances, potentially even marathons.

Obviously, if you eat a healthy variety of key nutrients already, you might not see major perks. (And in fact, not all the runners in DiSilvestro's study saw improvements.) But a lot of these minerals and amino acids are most commonly seen in organ meats and less-popular seafood, so you may be missing them. A balanced diet isn't always a complete diet, Rothschild adds.

Here, the experts share the most common vitamin deficiencies that may be preventing you from slaying full-force at the gym.


Iron is directly involved in transporting oxygen to the muscles, Rothschild says. Not only are women already at a higher risk because of our monthly blood loss, but iron deficiencies are also much higher in active women (and linked with poor physical performance!), according to a study in Current Sports Medicine Reports. Being an endurance athlete especially increases your issues: "The high number of repeated foot strikes while running can cause the destruction of red blood cells, increasing the need for iron replacement," Rothschild explains. And since most dietary sources of iron come from red meat, organ meat, eggs, and oysters, vegetarians are commonly deficient.


Zinc is crucial in all kinds of cellular functioning, including converting carbon dioxide into oxygen and vice versa, which affects our cardiorespiratory function, DiSilvestro explains. Its best dietary sources are oysters, beef, turkey, and pecans. But a recent study analysis in Sports Medicine found that despite higher dietary zinc intake, athletes tend to have lower levels of the mineral in their blood.


Copper helps metabolize carbohydrates, which means it directly affects energy levels, plus it helps keep your bones strong. If you eat a healthy variety of foods, you probably get a good dose of copper-its biggest sources are oysters, shellfish, organ meats, sunflower seeds, almonds, lentils, dark chocolate, and certain leafy greens. But some studies have suggested that young adult women are deficient, DiSilvestro says, so it's worth getting your levels checked. Both zinc and copper levels decrease after strength training and, to a lesser extent, after cardio, according to a study in the Journal of Sports Medicine and Physical Fitness.


If you're vegetarian or vegan, you probably already know you need to supplement with B12. It can definitely boost performance, as it's crucial in energy production, Rothschild says. But if you eat any form of animal products-meat, fish, eggs, milk-you're probably good. (Related: Why B Vitamins Are the Secret to More Energy)


An astonishing number of vegans and vegetarians are deficient in DHA, the fatty acid in fish oil, Rothschild says. A study published in Clinical Nutrition found that among vegans who didn't supplement DHA and EPA-two nutrients crucial for brain health-about 60 percent had low levels of DHA, and about 27 percent had very low levels, numbers similar to those who have brain shrinkage with aging. "There are several plant-based sources of DHA available, but this is something that should probably be supplemented by a woman not consuming fatty fish on a regular basis," he adds.


"Magnesium is involved in more than 300 metabolic reactions in the body, including maintenance of normal nerve and muscle function," says Rothschild. Good food sources include pumpkin seeds, cowpeas, almonds, and spinach, but this is another nutrient most people don't have high enough levels of, he adds.

Vitamin D

You're probably not surprised that D is on a list of vitamin deficiencies. But it may surprise you to learn that not popping the supplement may be inhibiting your performance (on top of these other weird health risks). Vitamin D has been linked with regulating over 900 gene variants and, in addition to the fact that a large number of active people are deficient, boosting levels may increase skeletal muscle function, decrease recovery time from training, increase force and power production, and boost testosterone levels, according to Canadian research. Sunshine is the best boost, but second to that is a supplement, Rothschild says.

Fix It

Based on the results of this study, DiSilvestro was prompted to develop a nutritional supplement for active women with the most bioavailable forms of some of these key nutrients. But Rothschild strongly advises getting your levels tested before you reach for his or any other supplement with these minerals, because how much you should take depends on how deficient you are.

"An iron overload can lead to a number of very serious problems (heart attack, diabetes, osteoporosis, to name a few from a very long list), with some people being genetically more susceptible than others. Taking too much zinc can be problematic because it can actually lead to a copper deficiency, which is also associated with a number of serious health issues," he explains.

So before you start supplementing, talk to your doc about it. Iron is the most common deficiency here and, luckily, is the cheapest of the tests to run, Rothschild says. You'll probably have to pay out of pocket to test your other mineral and nutrient levels, but those are less urgent, he adds.