Alicia Kendig, Carmichael Training Systems Sports Dietitian, writes The athletic supplement business is a multi-million dollar industry with products promising big boosts in performance from pills, powders, or liquids. As a sports dietitian, I’m bombarded by questions nearly every day regarding the benefits of these manufactured nutrients. In general, I’d like to see athletes get all their nutrients from food. After all, that’s where these vitamins and minerals occur naturally, and more and more research is pointing out the value and efficacy of swallowing multiple nutrients in say, a salad, as opposed to the isolated doses found in a supplement.

But, there are some nutrients that a hard-working athlete, one who’s working out multiple times a day several times a week, does need help with. That’s because all that exercise usually means they need an increase in vitamins and minerals—one they don’t have time to pull together from a wide-ranging diet. They’re either burning through more of these nutrients during their workout or losing them through sweat or waste. What all this boils down to is this: Athletes need to process a prodigious amount of food quickly and efficiently if they want to perform their best day after day. And to do that, they need micronutrients (vitamins and minerals).

There are several ways to keep your vitamin and mineral deposits full. One is a daily multivitamin that covers all your bases. From there I’ve put together the list, a short one, which itemizes three nutrients that athletes should strongly consider taking in a supplement.

MULTIVITAMINS:  These are the easiest, safest, and most convenient way for athletes to shore up their nutrient stores. Think of it as an insurance policy that guarantees that you get the stuff you need when a busy life gets in the way of preparing (or even finding) a variety of food.

Tip: Make sure to take these with a beverage or meal to decrease the chances of stomach upset.

VITAMIN C: Athletes who work out daily are going to experience an increase in muscle damage (Don’t worry, it’s how we grow stronger.) 500mg of Vitamin C, in addition to what you consume from foods each day, will help move that healing along.

Tip: Stay away from any supplement with over 500mg of Vitamin C. The recommended upper limit is 2,000mg a day from a supplement and food combination and any amount over that could lead to diarrhea and will end up as waste anyway.

IRON: I recommend that most female triathletes consider taking an iron supplement since the amount of strenuous exercise they do coupled with their generally small intake of red meat can make them iron deficient. In fact I see it a lot. What most women don’t understand is that they need a lot more iron than men, 18mg per day compared to 8mg for a guy. Vegetarian athletes also need additional iron (nearly double the amounts above) since iron from plant sources isn’t absorbed as easily as meat sources.

Iron’s a tricky mineral; too much can lead to constipation, loss of appetite, and vomiting. I advise clients to see their doctor for blood work to figure out how much iron is right for them.

Tip: If taking an iron supplement, don’t pop it along with dairy foods or teas; both contain elements that block considerable amounts of the mineral from being absorbed by your body. Citrus foods, however, optimize iron absorption.

CALCIUM: A study found that Masters’ women athletes consume up to 20 percent less calcium than their recommended daily minimum of 1,000mg. On top of that, the body excretes a sizable amount of calcium through sweat, a condition that can put the body in a calcium deficiency that could lead to bone density loss. For women and vegetarian men, a calcium supplement is a good call, assuming you’re already ingesting calcium-rich foods (dairy, fortified juices, green vegetables) to obtain the recommended 1,000 mg each day.

Tip: Vitamin D helps the body absorb calcium. You can get all you need simply by exposing your skin to the sun for 15 minutes, twice a week. Also note: the body can only process so much calcium at once, so limit your intake to no more than 500mg at a time. Any more could negatively affect normal kidney function and result in damage to your blood vessels and joints.

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