Exercise participation can increase your need for many nutrients, most notably water and energy. Whether vitamin and mineral needs are increased as well is still an issue of some debate. While some nutrients are almost certainly needed in higher amounts by intense exercisers, some nutrient requirements are probably no different for athletes than for couch potatoes. And, some nutrients can be thought of as specifically tailored for exercisers because they may improve athletic performance, yet have virtually no benefits for sedentary folks.
Because athletes and avid exercisers need to compensate for the high energy expenditure of training and competition, they generally consume more food and a higher number of calories than the average person. The extra calories serve to support the energy needs of exercise and maintain adequate energy stores of glycogen in the liver and muscles. The fact that you’re consuming more food to provide those needed calories also means that you’re getting an increased intake of vitamins and minerals - with the assumption that you’re making wise food choices and selecting those with a high nutrient density.
Although the increased energy needs of exercise are usually satisfied by a higher intake of the energetic nutrients (carbohydrates, protein and fat), it is important to keep in mind that vitamins and minerals play a vital role in the metabolic processes which are responsible for extracting the energy from foods. In addition to their role in energy production and storage, vitamins and minerals function as crucial co-factors for synthesis and repair of muscle tissue and red blood cells, and for protection of many tissues from the damaging effects of oxidative stress.
A number of micronutrients, most notably vitamins in the B-family, play a critical role as co-factors in energy metabolism. As co-factors, B-vitamins function as parts of enzymes involved in converting carbohydrates, proteins and fats in to energy. In some cases, B vitamin intake is tied to energy intake and protein intake. For example, the recommended dietary allowance (RDA) for three B vitamins; thiamin (0.5 mg), riboflavin (0.6 mg) and niacin (6.6 mg), is based on increments of 1000 calories consumed - (based on a 2,000 calories per day diet). Daily intake of another B-vitamin, B6, is based on protein intake (0.016 mg per gram of protein) because of its involvement in protein metabolism.
Thiamin is needed for metabolism of carbohydrate and branched chain amino acids (BCAA) - both of which play important roles in energy and fatigue during exercise. Riboflavin is necessary for the production of two key energy-generating enzymes - flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN) - which are needed during the metabolism of glucose, amino acids and fatty acids for energy. In addition to the role that vitamin B6 plays in amino acid and general protein metabolism, B6 also has crucial functions in energy production from carbohydrate - as in the conversion of lactic acid to glucose in the liver and the release of muscle glycogen to the bloodstream as free glucose.
While nutrient requirements based on energy intake may appear to be confusing, the good news is that, with a balanced diet and an adequate caloric intake, your B-vitamin intake is likely to take care of itself. The bad news, of course, is that if you’re satisfying your caloric needs with empty calories or highly refined or processed foods, there’s a chance that your intake of B vitamins is sub-optimal.
Feelings of Tiredness and Fatigue
Excessive feelings of tiredness and fatigue in athletes can sometimes be linked back to inadequate dietary intake of B vitamins, iron or carbohydrates. While vitamin B supplements and carbohydrate rich foods are often an effective and safe nutritional approach to combating fatigue, iron supplementation is not something to be taken lightly. Unless iron deficiency anemia is documented by a laboratory test (plasma ferrin analysis), high dose iron supplements should be avoided unless specifically recommended by your physician. In men, high does iron supplements can rapidly build up, with the potential for promoting tissue damage in heart, liver and muscles. If you think that you might need a bit more iron in your diet, a more prudent approach to boosting iron stores would be to consume an additional 100 mg of vitamin C at each meal to increase iron absorption.
Free Radicals and Oxidative Damage
Intense exercise can increase oxygen consumption 10-20 times over resting levels. A side effect of elevated oxygen consumption, however, is the generation of free radicals (electrically charged particles) and "oxidative stress" - which can damage tissues and cellular membranes. In defense of body cells and tissues, the body produces a variety of antioxidant enzymes that help to counteract many of the damaging effects of free radicals. In mounting its own antioxidant defenses, the body uses a number of minerals, such as zinc, copper, magnesium and selenium, in manufacturing enzymes to counterbalance the damaging effects of free radicals. In addition, other nutrients, like vitamins C and E, contribute to the body’s antioxidant defenses. Vitamin E is one of the most important fat-soluble antioxidants - providing crucial protection for cell membranes and internal cellular structures. Vitamin C, a water-soluble vitamin, performs important antioxidant functions within the blood and fluid compartments within and between cells of the body.
Both exercise and nutrition are known to influence the activity and responsiveness of the immune system to varying degrees. In most cases, moderate levels of exercise tend to bolster immune function, while extremely high intensity exercise and ultra-endurance events can sometimes temporarily suppress the immune system. In a similar manner, an inadequate intake of certain nutrients can reduce the response of immune system cells. In particular, vitamins A, B6, C, and E play a role in immune system function, such as maintaining the activity of specialized immune system cells like natural killer cells and CD4 cells.
In competitive athletes, a higher intake of vitamins C and E may help reduce their susceptibility to respiratory infections, colds and influenza - particularly following intense competitions such as triathlons and marathons.
Exercise / Nutrition Interaction
The relationship and interaction between exercise training, nutrient intake and athletic performance is incredibly complex and not well-understood. It is generally assumed that regular intense physical activity elevates somewhat the requirements for B-complex vitamins and vitamins C and E. It is also well accepted that the preferred route of satisfying this elevated requirement is through an increased consumption of whole grain carbohydrates, fruits and vegetables and low-fat meat and dairy products. Common dietary sources of the B vitamins are enriched grains - which typically add back the B complex vitamins at 25-100 percent of the RDA levels. Historically, highly processed foods, such as white rolls, white rice, honey and jam have been used in feeding studies to induce generalized B vitamin deficiency. In some cases today, however, highly processed foods, because of the enriched flour that forms the base of many of these foods, represents a significant portion of the B vitamin intake for many athletes. Other dietary sources are: Thiamin - pork and legumes, Riboflavin - eggs, lean meats and milk, vitamin B6 - chicken, tuna, beans, brown rice.
The Role of Supplements
Nutritional supplements may be warranted in many situations, particularly in cases of dietary restriction for weight loss or to attain a certain body weight goal. As general rule of thumb, a daily caloric intake of less than 1500 calories per day is unlikely to include a wide enough variety of foods to meet minimal requirements - so some form of dietary supplementation is often necessary.
True deficiencies of most B vitamins are rare in athletes consuming a mixed diet. Because of their role in energy metabolism, however, even a short period of sub-optimal intake can impair energy output and compromise athletic performance. In the case of B-vitamins, a sub-optimal intake of one is usually accompanied by a sub-optimal intake of others. A combined marginal intake of several B vitamins would be expected to impair physical performance in a matter of weeks and lead to more severe conditions such as anemia, muscle weakness and depression following prolonged periods of inadequate intake. In such cases, a multi-vitamin or B-complex supplement would be warranted.