Craig Moss has been running for 25 years and at the age of 44, is doing all he can to stave off any decreases in performance due to aging. He’s added more intensity to his runs, includes strides after easy runs and does a good amount of strength training two to three times each week.

Part of this plan of attack is dietary, as well. Moss includes daily supplements, three of them to be specific. For the past 18 months or so, he has added creatine and amino acids to reduce muscle loss and aid recovery, and l-carnitine for cardiovascular improvement.

Moss’ choice in supplements isn’t surprising: According to the National Institutes of Health, creatine and amino acids are among the most common supplements for athletes. According to one NIH study, as many as two-thirds of adult and adolescent track and field athletes take at least one supplement containing vitamins, minerals, creatine, caffeine or amino acids. The data also suggests that a larger proportion of athletes than the general population supplement, and the supplements used by male and female athletes tend to be similar, although women use more iron and men take more vitamin E, protein and creatine.

Moss says that he has been happy with the results of his supplementation. “I’ve noticed that my legs seem to recover faster,” he says. “I now can come back from a long run and do some lifting, something I couldn’t do before adding in the supplements. I also think I’m getting stronger. If a pill can help with that, then I want to take it.”

Many athletes who supplement do so on recommendations from friends or another trusted source. Moss made his selections based on advice he gleaned from a podcast.

While this might be the most common way for athletes to begin supplementation, Josh Emdur, MD, who heads up the running vertical for SteadyMD, cautions against it and has different advice for determining if, what and how much runners should add to their diets. “Runners should start thinking about nutrient deficiencies if they hit a plateau in training, aren’t recovering from an injury, or are experiencing unusually high levels of fatigue,” he says. “Even then, however, they should check with a physician to see what they might be lacking and to get a proper prescription for recovery.”

This is how 44-year old Nevada runner Janille Baker came to take a host of supplements, including hormones, fish oil, vitamin D and melatonin. “I was experiencing insomnia and weight gain, and it was pushing me over the edge,” she says. “A panel of blood tests showed that my iron and estrogen were both high, and my vitamin D, testosterone and progesterone were extremely low. This was the reason I was feeling so awful.”

Baker is slowly pulling out of her malaise and is hopeful the added vitamins and hormones will get her where she needs to be. Emdur says that cases like this are where supplements can play an important role. “Supplements should be intended to improve a nutrient deficiency,” he explains. “The first place for nutrition should be through a healthy diet.”

Think Before You Pop

Emdur makes an exception to his dietary rule in the case of runners who might be on a restrictive diet, such as vegan or gluten-free, or when they suffer from a condition that causes malabsorption of nutrients. “People with chronic digestive issues like Crohn’s, IBS or celiac might need something extra,” he says. “The same holds true for people who take certain medications, like diabetes drugs. These prescriptions tend to lead to B12 deficiencies, so it’s important to be aware of the side effects and check in with a physician on whether or not you need to supplement.”

Otherwise healthy athletes should proceed with caution, however. “Adding vitamins or other supplements into your diet isn’t always healthy and runners shouldn’t take them willy nilly,” he says. “I’ve seen cases where high doses of vitamin D or calcium have caused serious issues.”

Too much calcium, for instance, can lead to artery hardening. Take too much vitamin C or vitamin E and you might be increasing free radicals, which can up your odds for serious diseases like cancer down the road. Having too much vitamin D in your system can lead to loss of appetite, nausea and vomiting.

On the other side of the equation, even if they do no harm, supplements may not produce the desired effects. A recent study on the use of supplemental omega-3 fatty acids—long popular for helping reduce cardiac death—revealed only modest improvements in the subjects who were supplementing versus the control group.

So what’s a runner to do? Emdur recommends taking a hard look at your nutrition to identify any gaps, and getting annual bloodwork to further dial in any insufficiencies. “If you feel like something is off, see a doctor rather than self-diagnosing or adding some sort of supplement,” he says.

Moss did check in with his physician about the supplements he takes. “She told me that as long as I wasn’t seeing any side effects, there was no harm in them,” he says.

Emdur’s parting words of wisdom: “I can’t hammer it home enough,” he says, “supplements are meant to correct deficiencies. More is not better.”