You breathe in more oxygen when you exercise. As a result, free radicals form and damage muscle cells. Because antioxidants can reduce free-radical damage to muscle, some people think that taking them in a supplement might reduce muscle inflammation, soreness, and fatigue.

Does it work?

No. The free radicals that form when you exercise seem to help muscle fibers grow and produce more energy. Antioxidant supplements might actually reduce some of the benefits of exercise, including muscle growth and power output. Also, they have little effect on aerobic fitness and performance in endurance activities like distance running.

Is it safe?

Everyone needs adequate amounts of vitamin C and vitamin E for good health. Getting too much of these nutrients can be harmful, but the amounts of vitamin C (about 1,000 milligrams) and vitamin E (about 500 IU) typically used in studies of performance supplements are below safe upper limits. The side effects from coenzyme Q10 can include tiredness, insomnia, headaches, and some gastrointestinal (GI) discomfort, but these effects tend to be mild.

Bottom Line

There’s little scientific evidence to support taking supplements containing vitamins C and E or coenzyme Q10 to improve performance if you’re getting adequate amounts of these nutrients from a nutritious diet.

Arginine is an amino acid in foods that contain protein, like meat, poultry, fish, eggs, dairy products, and legumes. A nutritious diet supplies about 4 to 5 grams a day. Supplement sellers claim that taking larger amounts of arginine in supplements improves performance, partly because the body converts it into nitric oxide, which expands blood vessels and increases blood flow. Increased blood flow helps deliver oxygen and nutrients to exercising muscle and speeds up the removal of waste products that cause muscle fatigue.

Does it work?

Although the research is limited, arginine supplements seem to have little to no effect on strengthening and muscle-building exercises (like bodybuilding) or aerobic activities (like running and cycling). Studies have used 2 to 20 grams a day of arginine for up to 3 months.

Is it safe?

Arginine supplements seem safe when users take up to 9 grams a day for several days or weeks. Taking more can cause GI discomfort and can slightly lower blood pressure.

Bottom Line

There’s little scientific evidence to support taking arginine supplements to increase strength, improve performance, or help tired and sore muscles recover after exercise.

Beets and beet juice are among the best food sources of nitrate. Beet juice might improve athletic performance because the body converts some of this nitrate to nitric oxide, which expands blood vessels. This blood vessel expansion increases blood flow and the delivery of oxygen and nutrients to exercising muscle. The expanded blood vessels also speed up the removal of waste products that cause muscle fatigue.

Does it work?

Many, but not all, studies have found that beet juice can improve performance and endurance in aerobic activities like running, swimming, cycling, and rowing. But whether it helps with strengthening and bodybuilding exercises isn’t known. Beet juice is more likely to improve the performance of recreational exercisers than highly-trained athletes. The usual approach in studies is for participants to drink 2 cups of beet juice about 2.5 to 3 hours before exercise.

Is it safe?

Drinking moderate amounts of beet juice is safe, but it can turn your urine pink or red.

Bottom Line

Beet juice might improve aerobic exercise performance if you’re recreationally active. But whether dietary supplements containing beetroot powder have the same effects as beet juice isn’t known.

Beta-alanine is an amino acid in foods such as meat, poultry, and fish. People get up to about 1 gram a day of beta-alanine, depending on their diet. Your body uses beta-alanine to make carnosine in skeletal muscles. When you exercise intensely for several minutes, your muscles produce lactic acid, which reduces muscular force and causes tiredness. Carnosine reduces the buildup of lactic acid. Beta-alanine supplements increase muscle carnosine levels by different amounts, depending on the person.

Does it work?

Some, but not all, studies have shown that beta-alanine produces small performance improvements in swimming and team sports, like hockey and football, that require high-intensity, intermittent effort over short periods. Whether beta-alanine helps with endurance activities like cycling isn’t clear. It’s also not clear whether beta-alanine mainly benefits trained athletes or recreational exercisers. In most studies, participants took 1.6 to 6.4 grams a day of beta-alanine for 4 to 8 weeks.

Is it safe?

Taking 800 milligrams or more beta-alanine can cause moderate to severe paresthesia, a tingling, prickling, or burning sensation in your face, neck, back of the hands, and upper trunk. This effect can last 60 to 90 minutes but is not considered serious or harmful. Taking divided doses or a sustained-release form of beta-alanine can reduce or eliminate this paresthesia. It isn’t known whether it’s safe to take beta-alanine supplements daily for more than several months.

Bottom Line

Sports-medicine experts disagree on the value of taking beta-alanine supplements to enhance performance in high-intensity, intermittent activities. The International Society of Sports Nutrition recommends that if you are healthy and want to try beta-alanine supplements, take a daily loading dose of 4 to 6 grams per day (in divided doses with meals) for at least 2 weeks to see if it helps.

Your body converts a small amount of leucine, one of the amino acids in foods and protein powders, to HMB. Your liver then converts the HMB into another compound that experts think helps muscle cells restore their structure and function after exercise. HMB also helps build protein in muscle and reduces muscle-protein breakdown.

Does it work?

It’s hard to know whether you might benefit from using HMB supplements because the research on these supplements has included adults of very different ages and fitness levels who took widely varying doses for different amounts of time. Overall, HMB seems to speed up recovery from exercise that’s intense enough and long enough to cause muscle damage. Therefore, if you’re a trained athlete, you’ll need to exert yourself more than recreationally active people to cause the muscle damage that HMB might help treat.

Is it safe?

Studies haven’t reported any side effects in adults taking 3 grams per day of HMB for up to 8 weeks.

Bottom Line

It’s not clear whether taking HMB supplements will improve athletic performance. The International Society of Sports Nutrition recommends that if you are a healthy adult who wants to try HMB supplements, to take 3 grams per day in three equal servings of 1 gram for at least 2 weeks to see if it helps. HMB comes in two forms: one with calcium and one without. A dose of 3 grams of the type with calcium supplies about 400 milligrams of calcium.

Your body makes betaine, and it is also found in foods such as beets, spinach, and whole-grain bread. You get about 100 to 300 milligrams a day of betaine when you eat a nutritious diet. How betaine supplements might affect or improve your performance isn’t known.

Does it work?

Only a few, mostly small, studies have evaluated betaine as a performance supplement. Most of these studies examined the use of betaine supplements to improve strength and power performance in bodybuilders. The studies found either no performance improvements or only modest ones. Participants in these studies took 2 to 5 grams a day of betaine for up to 15 days.

Is it safe?

The few studies in which athletes took betaine supplements didn’t find any side effects. But there hasn’t been enough research to know for sure whether it’s really safe.

Bottom Line

There’s little scientific evidence to support taking betaine supplements to improve performance if you eat a nutritious diet.

The amino acids leucine, isoleucine, and valine are known as BCAAs. Animal foods, like meat, fish, and milk, contain BCAAs. Your muscles can use these three amino acids to provide energy during exercise. Leucine might also help build muscle.

Does it work?

There’s little evidence that BCAA supplements improve performance in endurance activities like distance running. BCAA supplements might help increase your muscle size and strength together with a weight-training program. But it isn’t clear whether taking BCAA supplements will help you build more muscle than just eating enough high-quality protein foods.

Is it safe?

A nutritious diet with enough protein can easily provide 10 to 20 grams a day of the BCAAs. Taking up to another 20 grams a day of BCAAs in supplements seems to be safe.

Bottom Line

There’s not much scientific evidence to support taking BCAA supplements to improve performance, build muscle, or help tired and sore muscles to recover after exercise. Eating foods containing protein automatically increases your intake of BCAAs.

Caffeine is a stimulant in beverages (like coffee, tea, and energy drinks) and in herbs (such as guarana and kola nut). Caffeine is also added to some dietary supplements. Moderate amounts of caffeine might increase your energy levels and reduce fatigue for several hours.

Does it work?

Caffeine might improve endurance, strength, and power in team sports. It’s most likely to help with endurance activities (such as distance running) and sports that require intense, intermittent effort (like soccer and tennis). Caffeine doesn’t help with short, intense exercise like sprinting or weightlifting. People have different responses to caffeine. It doesn’t boost performance in everyone, or may only slightly boost performance.

The usual dose of caffeine to aid performance is 2 to 6 milligrams per kilogram of body weight, or about 210 to 420 mg caffeine for a 154-pound person. (By comparison, a cup of coffee has about 85 to 100 milligrams of caffeine.) Taking more probably doesn’t improve performance further and can increase the risk of side effects.

Is it safe?

Caffeine intakes of up to 400 to 500 milligrams a day seem safe in adults. Teenagers should limit their caffeine intake to no more than 100 milligrams a day. Taking 500 milligrams or more a day can reduce rather than improve physical performance, disturb sleep, and cause irritability and anxiety. Taking 10,000 milligrams or more in a single dose (one tablespoon of pure caffeine powder) can be fatal.

Bottom Line

Sports-medicine experts agree that caffeine can help you exercise at the same intensity level for longer and reduce feelings of fatigue. They suggest taking 2 to 6 milligrams per kilogram of body weight 15 to 60 minutes before you exercise. The National Collegiate Athletic Association and International Olympic Committee limit the amount of caffeine that athletes can take before a competition.

Citrulline is an amino acid that your body produces; it is also present in some foods. Your kidneys convert most citrulline into another amino acid, arginine. Your body then transforms the arginine into nitric oxide, which expands blood vessels. This expansion increases blood flow and the delivery of oxygen and nutrients to exercising muscles and speeds up the removal of waste products that cause muscle fatigue.

Does it work?

The research on citrulline as a performance supplement is limited. The few studies find that citrulline might help improve, hinder, or have no effect on performance. In these studies, participants took up to 9 grams of citrulline for 1 day or 6 grams per day for up to 16 days.

Is it safe?

There isn’t enough research on citrulline to know for sure whether it’s safe. Some users have reported that it can cause stomach discomfort.

Bottom Line

There’s not much scientific evidence to support taking citrulline supplements to improve exercise or athletic performance.

What is Creatine?

Creatine is a compound that is stored in your muscles and supplies them with energy. Your body produces some creatine (about 1 gram a day), and you get some creatine from eating animal-based foods, such as beef and salmon (about 500 milligrams in a 4-ounce serving). But it is only when you take much larger amounts of creatine from dietary supplements that it might improve certain types of performance.

Does it work?

Creatine supplements can increase strength, power, and the ability to contract muscles for maximum effort. But the extent of performance improvements from creatine supplements differs among individuals.

Use of creatine supplements for several weeks or months can help with training. Overall, creatine enhances performance during repeated short bursts of intense, intermittent activity (lasting up to about 2.5 minutes at a time), such as sprinting and weight lifting. Creatine seems to have little value for endurance activities, such as distance running, cycling, or swimming.

Is it safe?

Creatine is safe for healthy adults to take for several weeks or months. It also seems safe for long-term use over several years. Creatine usually causes some weight gain because it increases water retention. Rare individual reactions to creatine include some muscle stiffness and cramps as well as GI distress.

Bottom Line

Sports-medicine experts agree that creatine supplements can improve performance in activities that involve intense effort followed by short recovery periods. It can also be valuable in training for certain athletic competitions. In studies, people often took a loading dose of about 20 grams per day of creatine (in four equal portions) for 5 to 7 days and then 3 to 5 grams a day. Creatine monohydrate is the most widely used and studied form of creatine in supplements.

Deer antler velvet supplements are made from the antlers of deer or elk before the antlers turn into bone. Deer antlers might contain growth factors that could promote muscle growth.

Does it work?

There’s been little research on use of deer antler velvet to improve performance in either strength or endurance activities. The few published studies have found no benefit from taking the supplement.

Is it safe?

Deer antler velvet hasn’t been studied enough to know whether taking it is safe.

Bottom Line

There’s no scientific evidence to support taking deer antler velvet supplements to improve exercise or athletic performance.

DHEA is a steroid hormone produced by the adrenal glands. Your body converts some DHEA into testosterone, the male hormone that enhances muscle size and strength.

Does it work?

There’s been little study of the use of DHEA supplements to improve performance. The few published studies (all in men) have found no benefit from taking the supplement. Muscle size or strength and aerobic capacity didn’t improve, and testosterone levels didn’t rise.

Is it safe?

DHEA hasn’t been studied enough to know whether it’s safe to take. Two small studies in men found no side effects. But in women, taking DHEA supplements for months can increase testosterone levels, which can cause acne and facial hair growth.

Bottom Line

There’s no scientific evidence to support taking DHEA to improve exercise or athletic performance. The National Collegiate Athletic Association and the World Anti-Doping Agency prohibit the use of DHEA in athletic competitions.

Ginseng is the root of a plant used for thousands of years in traditional Chinese medicine. Some experts believe that Panax (also known as Chinese, Korean, Japanese, or American) ginseng might improve stamina and vitality. Siberian or Russian ginseng has been used to fight fatigue and strengthen the immune system.

Does it work?

Several small studies have examined whether Panax or Siberian ginseng supplements can improve performance. This research provides little evidence that various doses and preparations of these supplements improve performance in athletes or recreational exercisers.

Is it safe?

Both Panax and Siberian ginseng seem to be safe. However, ginseng supplements can cause headaches or GI effects and disturb sleep.

Bottom Line

There’s little scientific evidence to support taking ginseng supplements to improve exercise or athletic performance.

Glutamine is an amino acid that your body uses to produce energy. Adults consume about 3 to 6 grams a day from protein-containing foods such as meat, poultry, fish, eggs, dairy products, and legumes. Your body also makes some glutamine, mainly from BCAAs.

Does it work?

Only a few studies have examined the use of glutamine supplements for improving performance in strengthening and muscle-building exercises (like bodybuilding) and for recovering from these exercises (for example, by reducing muscle soreness). Glutamine has either no effect or provides only a small benefit.

Is it safe?

Studies haven’t reported any side effects from the use of up to 45 grams a day of glutamine for several weeks in adults.

Bottom Line

There’s little scientific evidence to support taking glutamine supplements to improve exercise or athletic performance.

Iron is a mineral that delivers oxygen to muscles and tissues throughout your body. Cells also need iron to turn food into energy. Iron deficiency, especially with anemia, limits your ability to exercise and be active because it makes you tired and reduces your performance.

The recommended amount of iron to get each day is 11 milligrams for teenage boys, 15 milligrams for teenage girls, 8 milligrams for men to age 50, 18 milligrams for women to age 50, and 8 milligrams for older adults of both sexes. Recommended amounts are even higher for athletes, vegetarians, and vegans. Teenage girls and premenopausal women have the greatest risk of not getting enough iron from their diets.

Does it work?

For people with iron deficiency anemia, taking an iron supplement will probably improve performance in both strength and endurance activities. But if you get enough iron from your diet, taking extra iron won’t help. It’s not clear whether milder iron deficiency without anemia reduces exercise and athletic performance.

Is it safe?

Taking less than 45 milligrams of iron in a supplement is safe for teenagers and adults. Higher doses can cause upset stomach, constipation, nausea, abdominal pain, vomiting, and fainting. However, doctors sometimes prescribe large amounts of iron for a short time to treat iron-deficiency anemia.

Bottom Line

Taking enough iron in supplements to treat iron-deficiency anemia improves exercise capacity. But a healthcare provider should diagnose this condition before you start taking iron supplements. If you want to improve your athletic performance, you should eat a healthy diet containing foods rich in iron, such as lean meats, seafood, poultry, beans, nuts, and raisins. If needed, an iron-containing dietary supplement can help you get the recommended amount of iron.

Protein helps to build, maintain, and repair your muscles. It improves your body’s response to athletic training and helps shorten the time you need to recover after exercise. Protein is made from amino acids. Your body makes some amino acids but needs to get others (known as essential amino acids or EAAs) from food. Animal foods like meat, poultry, fish, eggs, and dairy products contain all of the EAAs. Plant foods like grains and legumes contain different EAAs, so eating a diet containing different types of plant-based foods is one way to get all EAAs. Most protein powders and drinks contain whey, a protein in milk that provides all the EAAs.

Does it work?

Adequate protein in your diet provides the EAAs necessary for making muscle proteins and reduces the breakdown of proteins in your muscles. Athletes need about 0.5 to 0.9 grams of protein per pound of body weight a day (or about 75 to 135 grams for a person weighing 150 pounds). You might need even more for a short time when you’re training intensely or if you reduce your food intake to improve your physique or achieve a competition weight.

Is it safe?

High intakes of protein seem to be quite safe, but there is no benefit to consuming more than recommended amounts.

Bottom Line

If you are an athlete, you can probably eat enough foods that contain protein to meet your needs for protein. If needed, protein supplements and protein-fortified food and beverage products can help you get enough protein. Sports-science experts recommend that athletes consume 0.14 grams of protein per pound of body weight (about 20 grams for a person weighing 150 pounds) of high-quality protein (from animal foods and/or a mix of different plant foods) every 3 to 5 hours, including before sleep and within 2 hours after exercising.

Quercetin is a compound found in fruits, vegetables, and some beverages (like tea). Some experts suggest that quercetin supplements increase energy production in muscle and improve blood flow throughout your body. A nutritious diet provides up to about 13 milligrams a day of quercetin.

Does it work?

There’s limited research on the use of quercetin supplements to improve performance. The studies found that any benefits, when they occur, tend to be small. In these studies, participants took about 1,000 milligrams a day of quercetin for up to 8 weeks.

Is it safe?

The studies of quercetin supplements didn’t find any side effects in the athletes who took them. But quercetin hasn’t been studied enough to know whether it’s really safe.

Bottom Line

There’s little scientific evidence to support taking quercetin supplements to improve exercise or athletic performance.

Ribose is a natural sugar your body makes that helps with energy production in muscle. Some scientists believe that ribose supplements help muscles produce more energy.

Does it work?

There’s been little study of the use of ribose supplements to improve performance. The few published studies in both trained athletes and occasional exercisers have shown little if any benefit from doses ranging from 625 milligrams to 10,000 milligrams a day for up to 8 weeks.

Is it safe?

The studies of athletes taking ribose supplements have found no side effects. But ribose hasn’t been studied enough to know whether it’s really safe when taken in large amounts for several months or more.

Bottom Line

There’s very little scientific evidence to support taking ribose supplements to improve exercise or athletic performance.

Sodium bicarbonate is commonly known as baking soda. Exercising intensely over several minutes causes muscles to produce acids, such as lactic acid, that reduce muscle force and cause tiredness. Sodium bicarbonate can reduce the buildup of these acids.

Does it work?

Studies show that athletes who take sodium bicarbonate might improve their performance a little in intense, short-term activities (like sprinting and swimming) and in intermittently intense sports (like tennis and boxing). But different athletes respond differently to sodium bicarbonate. Sodium bicarbonate might actually hinder performance in some people. The usual dose taken is 300 milligrams per kilogram of body weight, or about 4 to 5 teaspoons of baking soda. Some people find this amount of sodium bicarbonate, dissolved in liquid, too salty to drink.

Is it safe?

Sodium bicarbonate can cause GI distress, including nausea and vomiting, and weight gain due to water retention. It is also high in sodium (1,260 milligrams per teaspoon).

Bottom Line

Sodium bicarbonate might provide some performance benefit in strenuous exercise that lasts several minutes and in sports that require intermittent, intense activity, especially for trained athletes. However, in some people, sodium bicarbonate provides no performance benefit, and it can even reduce performance.

Tart or sour cherries of the Montmorency variety contain compounds that might help you recover from strenuous exercise. Specifically, these cherries might help to reduce pain, muscle damage from strength-related activities, and lung trauma from endurance activities that require deep, heavy breathing.

Does it work?

There’s limited research on tart cherry as a performance supplement. The studies that have been done suggest that it might help bodybuilders recover their strength faster and feel less muscle soreness after exercising. The supplements could also help runners race faster and be less likely to develop a cold or respiratory problem after a marathon. The typical dose is about 2 cups of juice or 500 milligrams of tart-cherry-skin powder for a week before the exercise and for 2 days afterwards.

Is it safe?

Studies of tart-cherry products in athletes have not found any side effects. But the safety of tart-cherry supplements has not been well studied.

Bottom Line

There’s limited scientific evidence to support taking tart-cherry products to improve exercise and athletic performance.

Tribulus terrestris is a plant containing compounds that some sellers claim can improve performance by increasing levels of several hormones, including the male hormone testosterone.

Does it work?

There’s limited research on the use of Tribulus terrestris supplements to increase strength or muscle mass. The few studies investigating it did not find that it had any benefit.

Is it safe?

Tribulus terrestris hasn’t been studied enough to know whether it’s safe. Studies in animals show that high doses can cause heart, liver, and kidney damage.

Bottom Line

There’s no scientific support for taking Tribulus terrestris supplements to improve exercise or athletic performance. Some sports-medicine experts advise against taking any dietary supplements claimed to boost testosterone.

Your buddy at the gym can’t say enough about the bodybuilding products he’s been taking to help build muscle mass and strength. You wonder, are they all safe to use?

According to CDR Mark S. Miller, Pharm. D., a regulatory review officer at the U.S. Food and Drug Administration (FDA), bodybuilding products that contain steroids or steroid-like substances are associated with potentially serious health risks, including liver injury. “Some of the liver injuries were life-threatening,” CDR Miller says.

CDR Miller was the lead reviewer assessing hundreds of adverse event reports made to the FDA from July 2009 through December 2016. Thirty-five reports showed evidence of serious liver injury.

In addition to liver injury, anabolic steroids have been associated with serious reactions such as severe acne, hair loss, altered mood, irritability, increased aggression, and depression. They have also been associated with life-threatening reactions such as kidney damage, heart attack, stroke, pulmonary embolism (blood clots in the lungs), and deep vein thrombosis (blood clots that occur in veins deep in the body).

These bodybuilding products are promoted as hormone products and/or as alternatives to anabolic steroids for increasing muscle mass and strength. Many of these products make claims about the ability of the active ingredients to enhance or diminish androgen, estrogen, or progestin-like effects in the body, but actually contain anabolic steroids or steroid-like substances, synthetic hormones related to the male hormone testosterone.

Bodybuilding Products May Contain Steroids

Cara Welch, Ph.D., a senior advisor in FDA’s Office of Dietary Supplement Programs, explains that many of these bodybuilding products sold online as well as in retail stores, are labeled as “dietary supplements.” “In fact,” she says, “many of these products are not dietary supplements at all; they are illegally marketed, unapproved new drugs.” FDA has not reviewed these products for safety, effectiveness, or quality before these companies began marketing.

CDR Jason Humbert, a regulatory operations officer in FDA’s Office of Regulatory Affairs, says that potentially harmful, sometimes hidden ingredients in products promoted for body building continue to be a concern. “The companies making these products are breaking the law by exploiting an easily accessible marketplace to get these products to consumers,” he says. “In the end, it’s consumers who are put in harm’s way by taking dangerous ingredients from products promoted as having miraculous results or making empty promises, and who may not understand the risks.”

Some who use bodybuilding products engage in “stacking,” (watch video) using multiple products (including stimulants or products providing false assurances of liver protection) to enhance results or “gains.” These combinations may put consumers at greater risk for serious and life-threatening reactions.

What to Do

If you’re taking any body building products that claim to contain steroids or steroid-like substances, FDA recommends that you stop taking them immediately because of the potentially serious health risks associated with using them, CDR Miller says. The agency also recommends that you:

• Talk to your health care professional about any body building products and/or ingredients you have taken or are planning to take, particularly if you are uncertain about those ingredients.
• Talk to your health care professional if you are experiencing symptoms possibly associated with these products, particularly nausea, weakness or fatigue, fever, abdominal pain, chest pain, shortness of breath, jaundice (yellowing of the skin or whites of the eyes), or brown or discolored urine.

FDA Taking Regulatory Action

In addition to issuing warning letters, CDR Humbert says, the agency can pursue other regulatory or enforcement actions against sellers of these illegal products. However, this can be challenging, particularly when sellers operate exclusively online. “Firm names or websites often are easily changed, or products can be relabeled in an effort to evade authorities and scam consumers,” CDR Humbert says.

The FDA encourages consumers and health care professionals to report adverse events or serious side effects related to the use of these products to the FDA’s MedWatch Safety Information and Adverse Event Reporting Program (MedWatch).

June 20, 2017

You probably know that a nutritious diet and sufficient fluids are important to maximize your physical performance. But you may wonder if certain dietary supplements could help you increase muscle strength, train harder, or improve performance. These types of supplements can’t take the place of a healthy diet, but some of them might have value for certain types of activity. Other supplements don’t seem to work, and a few might be harmful. Below are answers to some commonly asked questions about dietary supplements for exercise and athletic performance.

1. My son plays high school football, and many of his teammates drink energy drinks. Are they safe for teenagers?

The main thing to watch out for with energy drinks is the amount of caffeine they contain. Caffeine can cause nervousness, jitteriness, and difficulty sleeping, and at very high doses, it can cause heart problems and can even be fatal.

Caffeine might enhance performance in athletes when taken at moderate amounts before competition (about 200–400 milligrams [mg], depending upon body weight). Many energy drinks contain around 100 mg of caffeine per serving, but some may have more. Most adults can safely consume up to 400 or 500 mg of caffeine (about 4–5 8 oz. cups of coffee) in a day. For adolescents, however, the American Medical Association recommends no more than 100 mg of caffeine a day, and the American Academy of Pediatrics says that children and adolescents should not consume caffeine-containing energy drinks at all.

2. I’m training for a marathon and wonder if taking a creatine supplement would be helpful.

Creatine is a compound that is stored in your muscles and supplies them with energy. Your body produces some creatine, and you also get some creatine from eating animal foods such as beef and salmon. Creatine supplements provide much larger amounts of creatine (usually in the form of creatine monohydrate) than you can get from your diet.

Creatine supplements can increase strength, power, and the ability to contract muscles for maximum effort. But creatine is helpful only for repeated short bursts of intense, intermittent activity such as sprinting and weight lifting. For endurance activities like distance running, it appears to have little value. Creatine can cause weight gain because it tends to cause water retention, but otherwise, it is considered safe for healthy adults.

3. I am a 22-year-old male who is trying to build muscle by working out at the gym 4 to 5 days a week. I eat healthy foods, but I wonder if I should take protein powder to make sure I’m getting enough protein.

It depends on how much protein you’re already getting from the foods you eat. Athletes need about 0.5 to 0.9 grams of protein per pound of body weight a day. This works out to about 90 to 160 grams for someone weighing 175 pounds. This is more protein than less active adults need, but it is still possible to get this amount from protein-containing foods. These include meats, seafood, and poultry (a 3-ounce chicken breast has 27 grams of protein), eggs (one egg has 6 grams of protein), dairy products (1 cup of milk has 8 grams of protein), beans (1/2 cup of black beans has 7 grams of protein), and nuts (1 ounce of peanuts has 7 grams of protein). If needed, protein supplements and protein-fortified food and beverage products can help you get enough protein.

The other thing to consider is the “quality” of protein. Protein is made from amino acids. Your body makes some amino acids but needs to get others (known as essential amino acids or EAAs) from food. Animal foods contain all of the EAAs, but plant foods contain different ones. So if you consume mostly or only plant foods, eat a variety of them to make sure you’re getting all EAAs. Most protein powders and drinks contain whey, a protein in milk that provides all of the EAAs.

FDA warns that some bodybuilding products may not be safe

According to the U.S. Food and Drug Administration (FDA), some products that are promoted for increasing muscle mass and strength may contain steroid or steroid-like substances. These products are labeled as dietary supplements but are actually illegal, unapproved drugs, and they have been associated with serious health risks including liver injury. If you are taking any bodybuilding products that claim to contain steroids or steroid-like substances, stop taking them immediately and talk with your health care provider—especially if you are experiencing any symptoms such as nausea, weakness or fatigue, fever, abdominal pain, chest pain, shortness of breath, jaundice, or brown or discolored urine.