By Amy Culp
It may be the most-asked question sports dietitians get from athletes: How do I know if I'm getting enough vitamins and minerals for optimal performance? Right behind it come two more questions. What foods pack the most punch for vitamins and minerals? Should I take a supplement?
Here at the University of Texas, I am fortunate to collaborate with a dynamic group of athletic trainers, strength coaches, and sports medicine physicians to ensure our athletes are not deficient in their nutritional intake. Our student-athletes are screened for iron and vitamin D blood levels and offered nutritional consultations when they first arrive on campus. When needed, they are also provided nutrition intervention. And we continually educate Texas Longhorn student-athletes on all aspects of dietary health.
But even if you don't have access to the same resources--or are a one-person team for your school's sports medicine needs--there is much you can do to help your student-athletes meet their nutrient needs. It starts with understanding how micronutrients assist the body and continues with knowing the specifics of the key ones.
Student-athletes are often confused about how vitamins and minerals work, thinking they provide energy. Because they do not contain calories, micronutrients cannot boost energy stores. However, they are crucial for turning food into energy through metabolic pathways. For example, many B vitamins aid in energy being released from carbohydrates.
Other important roles of micronutrients include aiding in the production of oxygen-carrying proteins, maintenance of bone health, proper immune system function, and fluid balance. They also help with the synthesis and repair of new muscle tissue and protect against oxidative stress.
Since athletes have high rates of energy metabolism and need their bodies to function at intense levels, they tend to have higher micronutrient needs than non-athletes. In addition, exercise stresses the metabolic pathways where vitamins and minerals are utilized and may also result in biochemical adaptations that increase micronutrient needs. Routine exercise may also speed up the turnover and loss of vitamins and minerals from the body.
But how much additional vitamins and minerals do athletes need, and which ones? To begin to answer that question, it's important to understand Dietary Reference Intakes (DRIs), which are established by the Food and Nutrition Board of the Institute of Medicine. These provide a set of values used to plan and assess nutrient consumption and vary by age and gender. They include:
Recommended Dietary Allowance (RDA): average daily level of intake sufficient to meet the nutrient requirements of nearly all (97 to 98 percent) healthy people.
Adequate Intake (AI): established when evidence is insufficient to develop an RDA and is set at a level assumed to ensure nutritional adequacy.
Tolerable Upper Intake Level (UL): maximum daily intake unlikely to cause adverse health effects.
Because some athletes are tempted to mega-dose on vitamins and minerals, thinking it will give them a performance boost, they need to be acutely aware of UL numbers. Taking too much of a micronutrient will not help them play better and can cause harm by increasing the risk for toxicity (especially with fat soluble vitamins A, D, E, and K), as well as interfering with absorption and function of other micronutrients or medications.
The key is for athletes to figure out where they may be deficient and come up with a dietary plan to rectify those problems rather than popping supplements left and right. This doesn't mean they have to analyze all of the food they eat. But it does mean athletes should be aware of how their food choices affect their intake of vitamins and minerals.
Sports dietitians tend to practice a "food first" approach. We feel it's important for athletes to get a base performance-eating plan in place, and then fill in the gaps with dietary supplements. This is for many reasons, starting with the fact that eating is more fun than taking a pill!
Just as important, many of the nutritional deficiencies seen in athletes can be related back to an energy intake deficit in their daily diet. It is best to first identify and understand the barriers that stand in the way of meeting these needs, and then help athletes strategize for success. Satisfying caloric needs is essential for making gains in strength and performance goals, overall energy levels, immune system functioning, and hormonal balance. That cannot be replaced with a supplement.
Foods also appear to have a synergistic effect when consumed as part of a varied diet, which is difficult to duplicate by solely ingesting micronutrients. A great example of this is that some types of iron are difficult for the body to absorb and utilize when eaten alone, but when consumed with a food high in vitamin C, absorption is enhanced.
In order to ensure adequate amounts of micronutrients are obtained from whole foods, there are five factors to keep in mind:
Nutrient Density: Eating nutrient-dense foods is the best way to get vitamins and minerals. This means foods with lots of color (fruits, vegetables), whole grains, nuts, seeds, and a variety of lean protein sources (including some vegetable sources of protein, such as beans).
What I've found works well is to ask athletes to choose nutrient dense food 80 percent of the time. That leaves 20 percent of food choices for fun. Athletes can relate to this balance, and most find it doable.
To assist athletes in making their choices a little easier, I also provide recipes for foods that are nutrient dense. One is a kale, oat, and blueberry smoothie and another combines butternut squash with quinoa, spinach, and walnuts for a hearty side dish. An easy snack food I recommend to our athletes is mixing a variety of nuts such as peanuts, almonds, walnuts, and Brazil nuts with raisins, dried fruit, sunflower and pumpkin seeds, soybeans, and granola.
Balance: Athletes should also focus on getting the correct balance of macronutrients (carbs, protein, fat) from each of the food groups. Inevitably, some will try diet fads that will either include too many carbs or not enough carbs. Consuming the right ratio of carbs and protein will translate to having enough micronutrients in their diets.
Variety: Choosing a variety of foods from each of the food groups can help greatly with getting adequate vitamins and minerals. The more variety, the more likely it is athletes will satisfy all of their micronutrient needs.
Fortified Foods: Many foods today are fortified, especially those marketed to athletes. As athletes strive to get the right dosages of micronutrients, they need to be aware of the levels of vitamins and minerals in the fortified foods they consume. For example, nutritional shakes and bars can have large amounts of certain micronutrients that could cause an athlete to meet or exceed their needs without supplementation.
Food Quality: Advise athletes to choose fresh fruits and vegetables that are in season or frozen when they are not. Frozen fruits and vegetables are picked at the peak of their ripeness (when they contain the most nutrition) and flash frozen. Look for those that are in their original form and not covered in sauces or breading.
In addition, athletes should avoid overcooking vegetables, which causes micronutrients to diminish. Instead, they can steam, blanch, microwave, grill, or roast. These are all easy ways to cook vegetables and retain their nutrition.
PACK A PUNCH
In the above list, I put nutrient density first because it is the most important. Some foods are simply better than others for providing a lot of micronutrients. Below are some great choices for nutrient-dense foods:
Kale: This dark leafy green vegetable has become increasingly popular in the past few years. Part of the reason is because it is packed with nutrition. It is a good source of vitamins K, C, A, and B6, as well as calcium. It also contains natural antioxidants and fiber. Kale can be eaten raw in a salad, roasted with a little salt to make kale chips, or sautéed into a wide variety of recipes.
Butternut squash: This orange vegetable is high in fiber and antioxidants. It is also starchier than other squashes, making it higher in carbohydrates and a cleaner-burning fuel source. It is packed with vitamins A and C and potassium. It can be roasted, boiled, or mashed, and is great in risotto.
Whole grains: Grains, in their unrefined form, provide important vitamins and minerals as well as fiber. They are also a fuel source, and some (such as quinoa) contain higher amounts of amino acids than others. In addition, whole grains have a lower glycemic index than other carbohydrates, which causes less of a spike in blood sugar levels and allows for a longer duration of satiety.
Beans: Edamame, kidney, lentil, garbanzo, and black beans are considered an excellent source of both protein and carbohydrates. They provide a fair amount of magnesium, iron, folate, potassium, and fiber. They can be prepared in soups or stews, made into spreads, or placed on a salad.
Nuts: While nuts are high in fat, they provide unsaturated fats that have been shown to help decrease inflammation. They also provide protein, fiber, potassium, vitamin E, and folic acid. They are easy to make into a snack, can be added to many recipes, or used in cereal.
A CLOSER LOOK
Along with choosing a variety of nutrient-dense foods, some athletes should take a closer look at their micronutrient needs for a better understanding of each's significance. Most important to focus on for athletes are calcium, iron, zinc, magnesium, the B vitamins, and vitamin D, as well as some antioxidants such as vitamins C and E, beta-carotene, and selenium.
Let's start by looking at the key minerals: calcium, iron, zinc, and magnesium. Levels for these can be low, especially in female athletes. Inadequate energy intake or avoidance of animal products are typically the culprits.
Calcium: Most athletes understand that calcium is important for the growth, maintenance, and repair of bones. It has many other important tasks, such as regulation of muscle contraction, nerve conduction, and blood clotting.
There are two main forms of calcium supplements, if supplementation is needed: carbonate and citrate. Both forms are well absorbed, but individuals with reduced levels of stomach acid can absorb the citrate form more easily. Calcium carbonate is commonly available and inexpensive, and its absorption rate is most efficient when taken with food. Calcium citrate is absorbed equally effectively when taken with or without food. No more than 500 milligrams of calcium should be taken at a time to ensure optimal absorption and utilization.
Iron: An inadequate iron status is probably the most common micronutrient deficiency among athletes. Endurance athletes require approximately 70 percent more iron on a daily basis than the general population. When this goal is not achieved, performance declines because of less than optimal levels of hemoglobin, as well as changes in the muscle--reduced amounts of myoglobin and iron-related enzymes that are involved in energy production.
Hemoglobin and myoglobin are both oxygen-carrying proteins. The capacity to carry oxygen is essential for endurance exercise as well as for normal function of the nervous, behavioral, and immune systems. Iron deficiency, with or without anemia, can impair muscle function and limit work capacity.
Iron depletion is typically related to inadequate energy intake. There are other factors that can affect iron status, including following a vegetarian diet with poor iron availability, times of rapid growth in adolescence, training at high altitudes, and increased losses (sweat, urine, feces).
It is prudent to perform routine iron screenings, including serum ferritin levels, to determine possible supplementation needs. Also note that reversing iron deficiency anemia can take three to six months.
Good sources of iron include chicken and beef liver, Cream of Wheat, dried fruits, oatmeal, beans, lentils, and meats. Certain forms of iron from non-meat sources are absorbed more readily when foods with vitamin C are consumed at the same time. Also important to consider is that absorption is decreased when taken with tea, coffee, chocolate, dark leafy greens, whole grains, soda, and certain minerals. A good rule of thumb if iron stores are low is to consume calcium-rich foods and tea between meals. Also, focus on getting vitamin C-rich foods at meal times, especially when consuming non-meat iron sources.
Zinc: This mineral aids in the growth and repair of muscle tissue, energy production, and immune status. Basal metabolic rate, thyroid hormone levels, and protein utilization have been shown to be directly affected by zinc status. Athletes, especially women, who are at risk for impaired zinc status are those who consume a diet low in overall energy needs and animal protein, but high in fiber.
Athletes should be cautioned against single-dose zinc supplements because they often exceed the UL of 40 mg. Consuming too much zinc can lead to low HDL cholesterol and nutrient imbalances by interfering with absorption of other minerals, such as iron and copper.
Magnesium: Playing a variety of roles in the metabolism of carbohydrates, protein, and fats, magnesium also regulates neuromuscular, cardiovascular, immune, and hormonal functioning. Endurance performance is impaired by magnesium deficiency because of increasing oxygen requirements to complete submaximal exercise. Inadequate magnesium intake is typically related to overall energy deficit and an inadequate balance of food groups.
Besides the four key minerals, the B vitamins are next on the list of important micronutrients and include thiamin, riboflavin, niacin, pyridoxine (B6), pantothenic acid, biotin, folate, and B12. The B vitamins thiamin, riboflavin, niacin, B6, pantothenic acid, and biotin are involved in energy production during exercise. Folate and B12 are required for the production of red blood cells, protein synthesis, and in tissue repair and maintenance.
There has been some data to suggest that exercise may double the need for B vitamins. Severe deficiency of B12, folate, or both may result in anemia and reduced performance.
In terms of supplementation, B vitamins are water-soluble, thus are not stored in the body in the same way as fat-soluble vitamins. Also know that excess intake can lead to problems.
Vitamin D intake related to athletic performance is currently a hot topic. Although technically not a vitamin, this hormone is necessary for the absorption of calcium, making it essential for bone health. It also plays an important role in immune function and reducing inflammation.
In recent years, more research has been done on the consequences of vitamin D deficiency in athletes. It has been shown that low levels can decrease physical performance and increase the incidence of stress fractures. The RDA was increased from 400 IU to 600 IU in 2010 as more information about the prevalence of deficiency and its role in maintaining good health and optimal athletic performance was uncovered.
One more area to cover is antioxidants, particularly vitamins C and E, beta-carotene, and selenium, which play important roles in protecting cell membranes from oxidative damage. It has been hypothesized that frequent exercise produces a chronic oxidative stress on the muscles since exercise increases oxygen consumption, and thus ups the need for antioxidants. This idea remains controversial.
There is some evidence that a combination of antioxidants may be helpful at reducing inflammation and muscle soreness. Strenuous and prolonged exercise has been shown to increase vitamin C needs from 100 to 1000 mg/day. Athletes need to be advised to not exceed the UL for any antioxidant because higher doses could be pro-oxidative with possible negative effects.
ADDING IN SUPPLEMENTS
With our student-athletes at Texas, the goal is that they meet increased micronutrient needs through food alone. But that can be difficult to achieve consistently. This is especially true with athletes who have restricted eating patterns (intentional or unintentional), such as severe weight loss practices, disordered eating, a food allergy, or by following fad diets. A balanced, varied diet can also be tough for athletes with poor eating habits, inadequate finances, or an overcommitted lifestyle that causes erratic meal patterns.
Athletes falling into those categories would benefit from meeting with a sports dietitian and considering a daily multivitamin/mineral supplement. A basic multivitamin/mineral supplement can fill in the gaps when eating right is an issue. In some cases, here at Texas, individual nutrient supplementation, such as iron, calcium, or vitamin D, is recommended based on our protocols and my assessment of the athlete.
If an athlete's diet is adequate in calories and balanced most days with just some inconsistencies, I will often prescribe taking a multivitamin/mineral supplement every other day instead of daily. Another strategy I often use is to fill the nutritional gaps with fortified sports bars and other fortified foods that provide micronutrients.
Choosing a multivitamin/mineral supplement can pose challenges due to limited regulation of dietary supplements. This issue will not be discussed in detail here, but there are some important points to consider:
- Look for third party verification, such as Informed-Choice or NSF, which helps to ensure the safety of the dietary supplement.
- Avoid supplements marketed to burn fat, increase energy, or promise anything that sounds too good to be true.
- Avoid supplements that offer mega-doses of vitamins and minerals.
- For more in-depth information about dietary supplements, visit the helpful Web site:
In order to hammer home the importance of nutrition, we often tell our athletes, "You can't out-train a poor diet." The same could be said for supplements: "You can't out-supplement a poor diet." Multivitamin/mineral supplements are intended to fortify a strong nutritional foundation, and teaching athletes the importance of an overall adequate diet is the key to long-term success.
To view and download a handout on meeting iron needs, please visit www.Training-Conditioning.com/Iron_Handout.pdf
The author would like to thank Maria Pugliese, dietetic intern, for her assistance in conducting research for this article.
Sidebar: BREAKING IT DOWN
The following provides information on the most important vitamins and minerals for athletes. The Recommended Dietary Allowance (RDA) amounts listed for athletes and Tolerable Upper Intake Level (UL) are per day. The listings with ranges depend on caloric consumption.
RDA: Adult males and females: 1000 mg
UL: 2500-3000 mg
Best food sources include dairy products, leafy greens, calcium-fortified foods (juice, dairy alternatives), and legumes
RDA: Adult males: 8 mg, adult females: 18 mg
UL: 40-45 mg
Best food sources include liver, oatmeal, dried peaches and apricots, spinach, and meats
RDA: Adult males: 11 mg, adult females: 8 mg
UL: 40 mg
Best food sources include meat, fish, poultry, shellfish, eggs, whole grain foods, vegetables, and nuts
RDA: Adult males: 400-420 mg, adult females: 310-360 mg
UL: 350 mg
Best food sources include dairy products, meat, nuts, whole grains, leafy greens, and fruit
RDA: Adult males: 1.2 mg, adult females: 1.1 mg
UL: None known/established
Best sources include whole grain cereals, beans, pork, and enriched grains
RDA: Adult males: 1.3 mg, adult females: 1.1 mg
UL: None known/established
Best sources include dairy products, eggs, leafy greens, whole grain cereals, and enriched grains
RDA: Adult males: 16 mg, adult females: 14 mg
UL: 20-35 mg
Best sources include dairy, eggs, whole grains, meat, fish, poultry, and enriched grains
RDA: Adult males: 1.3-1.7 mg, adult females: 1.3-1.5 mg
UL: 60-100 mg
Best sources include meat, fish, poultry, eggs, beans, whole grains, seeds, and oysters
RDA: Adult males and females: 5 mg
UL: None known/established
Best sources include poultry, seafood, nuts, seeds, avocados, and whole grains
RDA: Adult males and females: 30 mcg
UL: None known/established
Best sources include egg yolks, legumes, leafy greens, and fish
RDA: Adult males and females: 400 mcg
UL: 600-1000 mcg
Best sources include enriched grains, dark leafy greens, whole grain breads and cereals, and citrus fruits
RDA: Adult males and females: 2.4 mcg
UL: None known/established
Best sources include seafood, meats, dairy, eggs, and fortified breakfast cereals
RDA: Adult males and females: 400-600 IU
UL: currently set at 4000 IU
Best sources include fortified milk and cereals, cod-liver oil, seafood, and eggs
RDA: Adult males: 90 mg, adult females: 75 mg
UL: 1200-2000 mg
Best sources include citrus fruits (oranges, grapefruits, and tangerines), strawberries, sweet peppers, tomatoes, broccoli, and potatoes
RDA: Adult males and females: 15 mg
UL: 600-1000 mg
Best sources include vegetable oils, nuts, and seeds
RDA and UL: Not established
Best sources include red, orange, yellow, and dark green fruits and vegetables.
Note: Excess intake of preformed vitamin A (retinol) has clear toxic effects when taken in excess of the maximum upper limit, but beta-carotene does not have these same toxic effects (although it may turn the skin a yellowish color!)
RDA: Adult males and females: 55 mcg
UL: 400 mcg
Best sources include meat, fish, seafood, whole grains, nuts, and seeds.
Amy Culp, RD, CSSD, LD, is an Assistant Athletics Director and the Sports Dietitian at the University of Texas. She has been coaching athletes on all aspects of fueling for optimal performance and health for over a decade and can be reached at: Amy.Culp@athletics.utexas.edu. NOTE: This article originally appeared in Training & Conditioning magazine, a sister publication of PrimeAthlete.