Micronutrient Needs for Athletes

In our previous blog post, we discussed the increased macronutrient needs of athletes and active individuals and why these are so important - from increased performance outcomes to injury prevention and recovery among many others. The macronutrients (protein, carbs and fat) often take the spotlight when it comes to nutrition, since, afterall, they are required by the body in the largest amount. However, of equal (if not more) importance are the micronutrients provided by the various protein, fat and carbohydrate options we have to choose from on a daily basis. 

Micronutrients are the nutrients the body requires in relatively small (“micro”) amounts which include vitamins and minerals. They play an essential role in the body, particularly when it comes to regulating processes such as energy production and the manufacturing of new cells and proteins (Maughan, et al., 2018). Micronutrient deficiencies can impair sports performance (and overall health) in a variety of ways, such as increasing an individual’s risk of illness or injury, or impacting his or her ability to train effectively. The metabolic and biochemical adaptations which occur during exercise, as well as increased nutrient turnover and/or loss, increase the need for certain nutrients in active individuals and athletes. Micronutrients of frequent sub-optimal consumption and therefore of key interest to athletes and active individuals include iron, vitamin D, calcium and antioxidants (Maughan, et al., 2018).

 Iron is an important component of red blood cells and is necessary to transport oxygen to our muscles. Iron deficiency can negatively impact physical and mental performance, as well as overall health (Volpe, et al., 2015) . Limited iron intake, poor bioavailability and/or inadequate energy intake are all risk factors for iron deficiency. Athletes who experience menstrual blood loss, foot-strike hemolysis (the rupture of red blood cells due to repetitive pounding on hard surfaces), excess losses in sweat, urine or feces and/or train at high altitude often have increased iron needs (Cowell et al., 2003). Female distance runners and vegetarians who may not be getting sufficient amounts of iron (particularly heme iron from animal sources) through their diet are at greatest risk for iron deficiency (Cowell et al., 2003). Oral supplementation can certainly be an effective solution for those with iron deficiency anemia; however, athletes and individuals concerned about iron status can adopt eating strategies to help ensure sufficient levels, such as consuming red meat, poultry, shellfish and organ meats. For athletes who abstain from meat consumption, vitamin C should be paired with plant-based iron sources such as beans/legumes, spinach and quinoa, as it aids in the absorption process (Thomas et al., 2016). At-risk athletes for iron deficiency should be regularly screened and aim for a daily iron intake above the Recommended Dietary Allowance (RDA) of 18mg for women, 8mg for men (Cowell et al., 2003).  

Vitamin D is an essential micronutrient for athletes in particular due to its important role in maintaining bone health and regulating the minerals calcium and phosphorus. Sufficient vitamin D status has been linked to decreased risk of stress fractures, acute respiratory illness and inflammation among others (Pojednic & Ceglia, 2014). Individuals who get plenty of sunshine and train mostly outdoors are at lower risk for vitamin D insufficiency compared to those with limited sun exposure; however, other factors such as skin tone, fat mass, training time, and clothing/equipment interfering with UVB exposure can alter risk for deficiency (Cannell et al., 2009). Dietary sources of vitamin D include fatty fish, beef liver, egg yolks, cheese, some fortified dairy and cereal products, and mushrooms; however, as a fat soluble vitamin, a fat source is required for optimal absorption. Unfortunately, dietary interventions alone have shown to be unreliable in resolving insufficiencies. Therefore, responsible UVB exposure and supplementation may be necessary to maintain sufficient status. Active individuals prone to stress fractures and other bone/joint injuries or with signs of overtraining, muscle pain or weakness and low sun exposure may require professional assessment to determine if vitamin D supplementation is necessary (Moran et al., 2013). 

Calcium plays an integral role in the growth, maintenance and repair of bone tissue, as well as muscle contraction, nerve conduction, and blood clotting. Individuals more susceptible to suboptimal calcium status tend to be those who restrict energy intake, display patterns of disordered eating, and/or avoid dairy products, putting them at greater risk for deficiency (Thomas et al., 2016). Foods high in calcium include dairy products such as milk, yogurt and cheese, as well as non-dairy options such as beans and lentils, almonds, dark leafy greens and figs. It’s important to note that even with sufficient calcium intake, vitamin D is essential for its absorption within the body, emphasizing the need for both nutrients. 

Even though physical activity is considered a key component of stress management and stress relief, exercise still creates internal stress within our bodies. When we engage in aerobic (requiring oxygen) exercise, our oxygen consumption increases significantly compared to rest. As a byproduct of this aerobic metabolism, reactive oxygen species (ROS) are produced. In relatively low amounts, such as with acute exercise and low-grade stress, ROS are beneficial to our health and play an essential role in the development and optimal functioning of every cell in our body (Thomas et al., 2016). Chronic stress (including chronic exercise-induced stress), however, can cause elevated intracellular levels of ROS and lead to oxidative stress. Oxidative stress occurs when there is a shift in the balance between oxidants and antioxidants in the favor of oxidants (Peternelj, et al., 2011). Antioxidants have the ability to attenuate the damaging effects of ROS. Our bodies generate their own antioxidant defenses; however, antioxidants are also found in food, especially fruits, vegetables and other plant-based whole foods. The safest and most effective strategy to increase antioxidant levels in the body is to consume a varied diet high in antioxidant-rich plant foods, such as berries, dark chocolate, green tea, kale, spinach, beans and nuts (Peternelj, et al., 2011). Individuals at greatest risk for low antioxidant intakes are those who restrict energy intake, follow a chronically low-fat diet, or limit intake of carbohydrates such as fruits, vegetables and whole grains (Thomas et al., 2016). Current research does not support the use of antioxidant supplementation as a means of combating exercise-induced oxidative stress, as high antioxidant doses have been shown to interfere with the positive effects of exercise and training-induced adaptations (Peternelj, et al., 2011). 

It’s important to note that while these micronutrient considerations provide a fundamental framework for athletes, nutrition needs vary based on the individual. Additionally, individuals with dietary limitations and/or avoidances may have increased micronutrient concerns. We recommend consulting with a registered dietitian to ensure adequate nutrient needs are being met in support of the demands of training and competition.

References:

Cannell, J.J., Hollis, B.W., Sorenson, M.B., Taft, T.N., & Anderson, J.J. (2009). Athletic performance and vitamin D. Medicine & Science in Sports & Exercise,41(5), 1102-1110.

Cowell, B.S., Rosenbloom, C.A., Skinner, R., Summers, S.H. (2003). Policies on screening female athletes for iron deficiency in NCAA division I-A institutions. International Journal of Sport Nutrition and Exercise Metabolism,13(3), 277-285.

Maughan, R. J., Burke, L. M., Dvorak, J., Larson-Meyer, D. E., Peeling, P., Phillips, S. M., … Engebretsen, L. (2018). IOC Consensus statement: Dietary supplements and the high-performance athlete. International Journal of Sport Nutrition and Exercise Metabolism, 28(2), 104–125. http://doi.org/10.1123/ijsnem.2018-0020

Moran, D. S., McClung, J. P., Kohen, T., Lieberman, H. R. (2013). Vitamin D and physical performance. Sports Medicine, 43(7), 601-611.

Peternelj, T. T., Coombes, J.S. (2011). Antioxidant supplementation during exercise training: Beneficial or detrimental? Sports Medicine, 41(12), 1043-1069.

Pojednic, R. M., Ceglia, L. (2014). The emerging biomolecular role of vitamin D in skeletal muscle. Exercise & Sport Sciences Reviews. 42(2), 76-81.

Thomas, D. T., Erdman, K. A., & Burke, L. M. (2016). Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and athletic performance. Journal of the Academy of Nutrition & Dietetics,16, 501-528. http://doi.org/0.1016/j.jand.2015.12.006

Volpe, S. L., Bland, E. (2012). Vitamins, minerals, and exercise. In Rosenbloom, C. A. & Coleman, E. J. (Eds.). Sports nutrition: A practice manual for professionals (5th ed.), (pp. 75-105). Chicago, Illinois: Academy of Nutrition and Dietetics.