This research review looks at the emerging news on micronutrients and how to apply the findings to your high-performance clients.
Rarely does a day go by without some new nutrition study making the news. The science of nutrients—especially specific vitamins and minerals—is dynamic, and new findings surface regularly. There can be a lot of information to keep straight, and we don’t get much help from the media, whose priority is the news hook. “The result can be incomplete information and, sometimes, inaccurate recommendations,” says Carol S. Lapin, MS, RD, CSSD, a certified specialist in sports dietetics and co- coordinator for the Wellness-CV group of the Sports, Cardiovascular & Wellness Nutrition (SCAN) dietetic practice group of the American Dietetic Association (ADA).
Adding to the confusion is a “ginormous vitamin and mineral supplement industry that benefits from fairly lax laws when it comes to health claims,” says Julie Upton, MS, RD, CSSD, and co-author of Energy to Burn (Wiley 2009). Between the claims being made by supplement manufacturers and the “breaking news” stories about small, sometimes suspect studies, the public may be excused for being more than a little confused.
As fitness professionals, you have clients who look to you for credible health information. And while it is always advisable to refer clients to a registered dietitian (RD) for more in-depth nutrition counsel, fitness professionals can help filter fact from fiction when it comes to vitamins, minerals and athletic performance.
Although nutrition experts agree that food is the preferred source of vitamins and minerals, there are cases where supplementation may be needed. Read on for an evidence-based update on the key vitamins and minerals that play an important role in sports nutrition, so you can remain confident that the information you share with clients is accurate, timely and within your scope of practice.
Good nutrition practices help balance the added metabolic stress that exercise creates. In addition to macronutrients (i.e., carbohydrates, protein and fat), the body needs micronutrients like vitamins and minerals to meet its increased needs and to promote overall good health. In sports nutrition, micronutrients have important roles in energy production; oxygen transport; bone health; preservation of a healthy immune system; and protection against free radicals that cause oxidative damage. Vitamins and minerals also help build and repair muscles after exercise or an injury.
The “greatest hits” list of vitamins and minerals that an athlete’s diet needs, but may be missing, includes the B vitamins; vitamin D; vitamins C and E; beta carotene and selenium; and calcium, iron, zinc and magnesium (ADA 2009). It is also important to get enough sodium and potassium in the right amounts, which can vary by individual. For a quick look at the recommended daily intakes of these and other important vitamins and minerals, see the sidebar “At a Glance: Current Recommended Intakes for Individuals and Upper Limits for Vitamins and Minerals Related to Athletic Performance.”
The B-vitamin complex is a group of eight water-soluble nutrients that are important for creating energy and keeping muscles healthy for physical activity. B vitamins are needed to make new red blood cells; create new proteins; and help repair tissues, including muscle tissue. The complex consists of thiamin, riboflavin, niacin, vitamin B6, pantothenic acid, biotin, folate and vitamin B12.
High-intensity performance may suffer when vitamin B status is low, and exercise can double the body’s need for riboflavin and B6 in particular (Woolf & Manore 2006). High-intensity activity (more than 12 hours per week) may also increase levels of homocysteine, an amino acid biomarker for heart disease that can be lowered by getting sufficient amounts of folate and vitamins B6 and B12 (Joubert & Manore 2008).
Red flags for low vitamin B status include poor diets, diets without enough calories, and diets that eliminate whole food groups (e.g., vegetarian diets) (Woolf & Manore 2006). “In such cases, I might consider recommending a multivitamin/mineral supplement, but I’d look at food solutions first,” says Jenna A. Bell, PhD, RD, CSSD, a blogger at www.chicagonow.com and co-author of Energy to Burn (Wiley 2009). “If the shortfall in B vitamins is linked to a diet that doesn’t provide enough calories, the easy and more holistic fix is to improve overall intake levels in a healthful, well-balanced way.”
A clinical deficiency in the B vitamins that assist with red blood cell production (folate and B12) may result in anemia. The resulting impaired ability to transport oxygen throughout the body impacts endurance athletes most. Because it can take about 3 months before the first signs of anemia are detected, encouraging athletes to get adequate intake levels earlier rather than later in the training process is a good idea. Food sources for B vitamins include whole grains, leafy greens, beans and peas, fish, lean poultry and meat, eggs, and low-fat or nonfat dairy.
The bottom line on B vitamins is that a deficiency will hurt performance, but there is currently not enough evidence to say that supplementation may improve it (ADA 2009).
If there’s one micronutrient that’s been singled out in the news of late, it’s vitamin D. This vitamin has come a long way from being calcium’s bone health sidekick. That said, its role in promoting bone health remains key to optimal human health and athletic performance and is one of the main reasons to encourage athletes to get enough of this important nutrient. Now, recent research points to an array of benefits, from heart health to lowering the risk of certain cancers.
Some researchers have gone as far as to say that “vitamin D deficiency is implicated in most of the diseases of civilization,” citing findings on the vitamin’s potential to prevent viral respiratory disease, cancer, osteoporosis, heart disease, multiple sclerosis, diabetes and high blood pressure (Cannell & Hollis 2008).
While the emerging research is worth paying attention to, whether the vitamin can live up to all of its potential health benefits remains to be seen. “Large population-based studies may show there’s a benefit associated with taking certain vitamins and minerals such as vitamin D, but it’s more difficult to determine a causal relationship that makes direct connections,” says Upton.
Nevertheless, experts have been ringing the bell to make people more aware of vitamin D deficiencies and to call for an increase in the recommended intake level. Citing convincing evidence of benefits and safety, an influential and international group of nutrition experts recently appealed to the media and policymakers to help improve vitamin D status worldwide (Vieth et al. 2007). The American Academy of Pediatrics has already taken an official position on vitamin D, recommending that children double the current guideline (for both adults and children) of 200 International Units (IU) per day to 400 IU per day (Wagner & Greer 2008).
Results from a large meta-analysis of 18 randomized controlled trials suggest that adults who take a daily supplement in the 400–830 IU range may decrease their risk of all-cause death (Autier & Gandini 2007). The current Tolerable Upper Intake Level (UL) for vitamin D (from diet and any supplements) is 2,000 IU for adults (Institute of Medicine [IOM] 1997), but significant research has emerged since this threshold was set more than a decade ago. More recent studies have shown that higher intakes up to 10,000 IU are not necessarily harmful, but these trials did not address any long-term side effects (Cranney et al. 2007).
In terms of cancer protection, the beneficial mechanism appears to be the vitamin’s ability to keep cells functioning in a healthful manner, promoting cell renewal as well as preventing unwanted multiplication. Citing vitamin D’s ability to increase levels of a naturally occurring antibiotic, some experts recommend daily intakes of 2,000–7,000 IU per day in otherwise healthy people (Cannell & Hollis 2008). However, these same experts strongly advise that vitamin D therapy should be added on to, and should never replace, standard cancer treatment.
Some clients may be unable to get enough sun exposure year-round to achieve the daily recommended levels of vitamin D because of geographical location or because they train indoors. Some individuals fear that sun exposure may increase their risk of skin cancer, which is why the American Academy of Dermatology (AAD) recommends getting the vitamin through food or supplement sources (AAD 2009).
When it comes to fitness benefits, there is evidence that vitamin D may improve athletic performance, especially in older adults (Cannell et al. 2009). Peaks and valleys in performance seem to line up with seasonal changes in vitamin D status, which increases with sun exposure. Vitamin D also helps fast-twitch muscle fibers to multiply and grow. Because vitamin D can affect bone health, immunity, inflammation and muscle function, it follows that athletes with low levels of the vitamin may suffer from poor bone health and exercise-related immunity and inflammation.
Heather Mangieri, MS, RD, CSSD, and owner of Nutrition CheckUp LLC, a private practice in Pittsburgh, talks about vitamin D with all her clients and encourages them to get tested for deficiencies. She informs them of the three main ways to get enough vitamin D—safe sun, food and supplements—and then explores which one might work best for their lifestyle.
The selection of foods with naturally occurring vitamin D is limited and includes fatty fish, sun-dried mushrooms and egg yolks. The still-small but growing list of foods fortified with vitamin D includes different kinds of milks (e.g., soy, almond, rice, oat, cow), orange juice, yogurt and breakfast cereals. In addition to food sources, safe sun exposure or a daily dietary supplement of 1,000–2,000 IU may be good options (Willis, Peterson & Larson-Meyer 2008). This is one vitamin for which supplementation may be a good idea, because it is not widely available in foods.
Vitamins and minerals that protect cells from free radicals, which cause oxidative stress, are categorized as antioxidants. Vitamins C and E, beta carotene and selenium are the major antioxidant nutrients that impact and are impacted by physical activity. Clients who follow a low-fat diet, restrict their calories or limit their intake of fruits, vegetables or whole grains have an increased risk of falling short of adequate antioxidant intake. A diet that does not supply enough antioxidants will affect athletic performance as well as overall health.
That said, taking supplements of these micronutrients has not been shown to improve performance. Indeed, overdoing it with antioxidant supplements can actually increase one’s overall risk of death (Bjelakovic et al. 2008).
An active body consumes significantly more oxygen than a less active body, so it follows that regular physical activity may result in a persistent state of oxidative stress and, therefore, greater antioxidant needs. Logical as it may sound, this theory is controversial. For example, conflicting results from a small, controlled trial showed that levels of vitamin E and beta carotene were higher in athletes than nonathletes, even when both groups had comparable diets; these results suggest that regular exercise may actually improve antioxidant status (Watson, MacDonald-Wicks & Garg 2005).
When it comes to antioxidants, there are plenty of dietary sources that meet our daily needs. Remind clients that food sources make “overdosing” less likely, that getting more than enough will not result in better performance and that too much could ultimately be harmful. In addition, because antioxidants work together synergistically, taking a single-nutrient supplement actually causes an imbalance.
Here’s a look at three specific antioxidants: vitamin E, vitamin C and selenium.
Athletes are not usually at risk of low vitamin E status, despite typically getting less than the recommended 12 grams per day (g/d); this may be because aerobic exercise improves absorption of vitamin E (Margaritis & Rousseau 2008). Aerobic exercise increases concentrations of healthy HDL cholesterol, which is also a vitamin E carrier; then, specific receptors act to send vitamin E to muscle cells.
But don’t go upping your daily intake of vitamin E yet. These same receptors decrease when muscles are high in vitamin E, so adding supersized amounts through supplementation won’t affect muscle stores. Plus, high levels in the blood are not desirable and may mean the body is in a state of heightened oxidative stress. Doses much higher than the recommended 15 milligrams per day (mg/d) (e.g., 536 mg/d) may increase exercise-induced oxidation (Margaritis & Rousseau 2008).
Vitamin E can be found in wheat germ oil, almonds, sunflower seeds or oil, safflower oil, hazelnuts, peanuts and peanut butter, corn oil, spinach, broccoli, soybean oil, kiwi and mango.
The recommended daily intake of vitamin C is 75 mg/d for adult women and 90 mg/d for men. High doses of vitamin C (above 500 mg/d) have been found to accelerate oxidation, which can lead to muscle damage and iron losses (Margaritis & Rousseau 2008).
Athletes do require more of this essential vitamin than sedentary people. However, too much vitamin C reduces the body’s ability to absorb other important nutrients, such as copper and zinc. Thankfully, the body does a good job of self-regulating dietary vitamin C. The body tops out its stores at around 200 mg/d, after which anything extra is excreted through urine (Margaritis & Rousseau 2008).
From a practical standpoint, it is feasible to obtain more than 200 mg/d of vitamin C through fruits and vegetables, so supplementation is seldom necessary. And since all fruits and vegetables provide some vitamin C, recommending food first is easy. Good options include peppers, citrus, strawberries, tomatoes, broccoli, leafy greens, potatoes, cantaloupe, Brussels sprouts, berries and squash.
When selenium stores are low, certain organs of the body (e.g., the brain and endocrine organs) get priority over muscles. When selenium is deficient, kidney and liver tissues can die. While it is important to get enough selenium, the scientific evidence on the effectiveness of supplementation (in the range of 50–180 micrograms per day [mcg/d]) is mixed (Margaritis & Rousseau 2008). As with vitamin C, the body holds on to what it needs and excretes the rest.
It is best to look for a variety of plant and animal sources of selenium, such as tuna, lean beef, cod, lean poultry, enriched pasta, whole eggs, low-fat cottage cheese and brown rice.
Athletes, especially female athletes, may not be eating enough total calories to meet their needs for calcium, iron, zinc and magnesium. Because these minerals are often found in animal products, vegans and vegetarians may be at an increased risk as well (ADA 2009). Sodium and potassium, two essential electrolytes, are especially important for endurance athletes who sweat for prolonged periods of time and may have higher needs.
As discussed earlier, calcium and vitamin D play a major role in the development, maintenance and repair of bone tissue. This important mineral also regulates muscle contraction, nerve function and normal blood clotting, which is essential to healing. Because low bone mineral density raises the risk for fractures, and because female athletes who restrict calories or avoid animal products are especially at risk, two authoritative organizations have recently taken a position on calcium.
Although the recommended daily intake for calcium is currently 1,000 mg/d, the International Olympic Committee (IOC 2009) and the American College of Sports Medicine (Nattiv et al. 2007) both recommend increasing that intake to 1,500 mg/d for athletes with disordered eating, amenorrhea or risk of early osteoporosis; the two groups also suggest increasing daily vitamin D intake from 200 IU to 400–800 IU for these same athletes.
Food sources of calcium include low-fat or nonfat yogurt and milk, sardines, cheddar cheese, fortified orange juice, tofu made with calcium sulfate, salmon with bones in and cooked spinach. Supplementation may benefit clients who don’t get adequate amounts of calcium through diet.
All athletes need more oxygen than their less active counterparts. Iron helps oxygen travel throughout the body; it is also involved in energy production and normal functioning of the nervous, behavioral and immune systems. Endurance athletes, such as long-distance runners, need about 70% more iron than the average person (IOM 2001). Because iron deficiency can quickly turn into anemia, preventing and treating the condition should start early in training, and supplementation may sometimes be advisable.
If a client is deficient in iron, supplementation can increase oxygen uptake, lower heart rate and decrease the concentration of exercise-induced lactate. In recent findings, iron-deficient women who took 100 mg/d of iron supplementation (in the form of ferrous sulfate) for 4–6 weeks had a decrease in skeletal muscle fatigue (Brownlie et al. 2004).
Clients can find iron in dried beans, dried fruit, eggs, fortified cereals, liver, lean red meat, oysters, poultry, salmon, tuna and whole grains.
This mineral is essential for maintaining healthy muscles, energy production and immune functioning. A zinc deficiency can lead to compromised cardiorespiratory function, reduced muscle strength and lower endurance (Lukaski 2005). However, excess zinc can lower healthy HDL levels and may interfere with the absorption of copper and iron. Further, the evidence on zinc’s ability to improve performance is weak (ADA 2009).
Oysters are a zinc superstar, but good amounts can also be found in crab, beef, pork, fortified cereals, poultry, lobster, cashews, yogurt, chickpeas and almonds.
It’s difficult to think of any physiological process that doesn’t require magnesium. This mineral is vital to the metabolic process and is involved in breaking down carbohydrates, fats and proteins. It is also involved in nerve, muscle, heart, immune and hormone functions.
A lack of magnesium can affect an athlete directly in that it increases oxygen needs. Athletes who are concerned with maintaining weight class (e.g., wrestlers) or who are very body conscious (e.g., ballerinas, gymnasts and tennis players) are at risk for poor magnesium status because of their restrictive eating habits (ADA 2009).
Magnesium-rich foods include halibut, almonds, cashews, soybeans, spinach, nuts, cereal, fortified oatmeal, baked potatoes with skin, peanuts and peanut butter, wheat bran, black-eyed peas, plain low-fat or nonfat yogurt, brown rice and lentils.
Much maligned in the media, sodium is actually an athlete’s friend. It is an essential electrolyte, and anyone who sweats is losing sodium. The UL for most people is 2,300 mg/d, but endurance athletes and those who sweat a lot may need more. Sodium needs vary widely, and replenishment quantities should be individualized.
Most Americans consume too much sodium from processed foods. It is best to get daily sodium from fruits, vegetables, whole grains and lean meats.
On the opposite side of the fence, potassium has become something of a media darling owing to its role in lowering high blood pressure. However, potassium does not need to be replenished at the same rate as sodium.
A well-balanced diet full of fruits, vegetables, nuts, seeds, low-fat and nonfat dairy, lean meats and whole grains should provide adequate potassium (Sawka et al. 2007). For physical activity lasting more than 2 hours, athletes can replenish electrolytes with sports drinks offering 500–700 milligrams per liter (mg/L) of sodium and 800–2,000 mg/L of potassium (ADA 2009).
Sports dietitians understand both sides of the wellness equation: energy in and energy out. They know how to best fuel a client for athletic performance as well as overall health.
“A lot of the athletes I work with love homemade trail mix,” says Christopher R. Mohr, PhD, RD, CSSD, of Mohr Results Inc., in Louisville, Kentucky. “It is easy, transports well and can be loaded with nutrients.” Mohr recommends including pistachios for their fiber and good-fat content (the unsaturated kind) and fruit for a mix of vitamins and minerals.
“We’ve found that our athletes often overlook calcium, as they are so focused on consuming adequate carbohydrate or protein,” say The Nutrition Twins®, Lyssie Lakatos, RD, CFT, and Tammy Lakatos Shames, RD, CFT, authors of The Secret to Skinny (HCI 2009). The two, who are based in New York City, often recommend calcium to clients who have been sidelined by stress fractures. They also advise eating a variety of foods, such as dairy products; leafy greens; broccoli; and calcium-fortified foods, like soymilk, tofu and orange juice.
“My motto is food first,” says Marie Spano, MS, RD, CSCS, of Spano Sports Nutrition Consulting in Atlanta. “The greater variety of foods you eat, the more likely you are to obtain an array of nutrients.”
Carol Lapin, MS, RD, CSSD, of Houston, keeps track of her clients online and teaches them how to bridge any nutrient gaps she sees in their diets. “I provide lists of the top 10 foods for the nutrients my clients fall short in.” Simple handouts that show clients the best food sources of vital vitamins and minerals are an effective educational tool.
If a particular client has been advised to take a supplement because of a deficiency, Julie Upton, MS, RD, CSSD, advises letting that individual decide when in the day to take it. “I think the best way is any way that they remember,” she says.
Because nutrient needs are greater in people who are very physically active and want to maintain optimal cellular function and performance, Jeffrey Blumberg, PhD, professor of nutrition science and policy at Tufts University, offers this advice to athletes: “Choose foods that are rich in vitamins, minerals and phytonutrients like fruit, vegetables and whole grains, but relatively low in calories. For good sources of protein, select lean meat low in saturated fat and fatty fish rich in omega-3 fatty acids.” When it comes to taking a vitamin and mineral supplement, Blumberg cautions, “dietary supplements cannot substitute for healthy food choices, but these products may be useful to ensure you are meeting all your nutrient needs.”
One thing is certain: New findings on vitamins and minerals will be ballyhooed in the media, and clients will have questions. They will look to you to put the news into context. Remind them that a healthful, well-balanced diet is always a good foundation. Caution them not to get swept up in the allure of supernutrients or superfoods, because classifying foods as “good” or “bad” can lead to disordered eating. Remind them that supplements won’t improve their performance if they are eating a nutritious diet.