The Effect of Physical Activity on Thiamin, Riboflavin, and Vitamin B6 Requirements

Two questions have frequently been asked by individuals engaged in physical activity: Does exercise increase the need for certain vitamins? and Does vitamin supplementation improve exercise performance? These are particularly relevant and timely questions with regard to thiamin, riboflavin, and vitamin B6, because these three vitamins are cofactors for many metabolic reactions that produce energy. In addition, the Recommended Dietary Allowances (RDAs) for these nutrients are dependent on energy (thiamin and riboflavin) and protein (vitamin B6) intakes. It may be logical to assume that as an individual becomes more physically active, both energy and protein intakes will increase along with the intake of these vitamins; however, this is not always true. If an individual makes poor dietary choices, these micronutrients may not increase with energy and protein intakes. Conversely, if an individual increases physical activity and restricts energy intake, the need for the vitamins may increase but the dietary intake would not.


Dietary Sources

Thiamin, riboflavin, and vitamin B6 are water-soluble B-complex vitamins found in a variety of animal and vegetable products. More specifically, thiamin is found abundantly in lean pork, yeast, legumes, and enriched cereals and breads. Riboflavin is found in eggs, lean meats, milk, milk products, broccoli, and enriched breads and cereals. Vitamin B6 is abundant in meats, especially chicken and tuna, and plant foods such as beans, cereals, and brown rice. These vitamins are also frequently added to commercially prepared foods at 25-100 percent of the RDA per serving. Thus, the consumption of fortified cereals, breakfast bars, sport bars, energy shakes and/or meal-replacement products (e.g., Ensured, Boosts, GatorPro~) will dramatically increase total dietary intakes. These types of products are frequently used by individuals who “watch their weight” or who are engaged in physical activity. In addition, any multivitamin or vitamin/mineral supplement will usually contain 100 percent or more of the RDA for these nutrients. It is estimated that millions of Americans use dietary supplements. The estimates are as high as 50 percent for individuals engaged in physical activity. Thus, the total intake of these vitamins in the diet of active Americans may be increasing regardless of dietary choices.


Exercise-related Functions and Requirements

Thiamin, as thiamin pyrophosphate, is important for the metabolism of both carbohydrate and the branched-chain amino acids (BCAA). It is a coenzyme for the pyruvate dehydrogenase complex that catalyzes the conversion of pyruvate to acetyl CoA. Thiamin is also a coenzyme for a-ketoglutarate decarboxylase, an enzyme responsible for the formation of succinyl CoA in the tricarboxylic acid (TCA) cycle, and for branched-chain decarboxylase, an enzyme responsible for the catabolism of the BCAA. Physical activity stresses these metabolic pathways for the production of energy. Because thiamin requirements are linked to energy metabolism, the RDA for thiamin is expressed in terms of energy intake. The current U.S. recommendation is 0.5 mg/1,000 kcal, with a minimum of 1.0 mg/day required for adults. An additional 0.4 and 0.5 mg/day are recommended during pregnancy and lactation, respectively.


Riboflavin is necessary for the synthesis of two important coenymes in the body-flavin mononucleotide (FMN) and Gavin adenine dinucleotide (FAD). These coenymes are especially important in the metabolism of glucose, fatty acids, glycerol, and amino acids for energy. Similar to thiamin, physical activity stresses the biochemical pathways that metabolize these substrates. The dietary requirement for riboflavin is also expressed in terms of energy intake. The current U.S. recommendation is 0.4 mgtl,OOO kcal for people of all ages, with a minimum intake of 1.2 mg/day. Because pregnancy and lactation increase energy demands, an additional 0.3 mg/day is recommended during pregnancy and an additional 0.~.05 mg/day is recommended during lactation.


A major function of vitamin B6 is the metabolism of proteins and amino acids. The most metabolically active form of vitamin B6 is pyridoxal 5′-phosphate (PLP). PLP is a cofactor for transverses, transaminases, decarboxylases, and other enzymes used in the many metabolic transformations of amino acids. During exercise, the gluconeogenic process involves the breakdown of amino acids for energy in the muscle and the conversion of lactic acid to glucose in the liver. Another function of vitamin B6 directly related to energy production during exercise is the breakdown of muscle glycogen. Thus, adequate vitamin B6 must be present to release glucose-1-phosphate from muscle glycogen. Because vitamin B6 is directly involved in amino acid metabolism, the requirements for vitamin B6 are expressed in terms of protein intake. The current U.S. recommendation for adults age 25 or older is 0.032 mg of B6/g of protein. As with thiamin and riboflavin, vitamin B6 requirements increase slightly with pregnancy and lactation (0.032-0.036 mg B6/g protein).


Rationale for Increased Need

Because exercise stresses metabolic pathways that use thiamin, riboflavin, and vitamin B6, it has been suggested that the requirements for these vitamins are increased in athletes and active individuals. Theoretically, exercise could increase the need for these nutrients in the following ways: increase the turnover, metabolism, or loss of the nutrient; increase the enzymes that require the nutrient; or increase the need for the nutrient for tissue maintenance and repair. Although biochemical evidence of vitamin deficiencies in some active individuals has been reported for these nutrients, studies examining these issues are limited and equivocal. Reasons for these inconsistencies may be related to a number of factors: dietary control, type and intensity of exercise, status indices measured, level of regular physical activity, type of subjects, or lack of a control group.


We do know that exercise increases both energy and protein needs and, thus, also increases the total daily needs of thiamin, riboflavin, and vitamin B6 in active individuals. However, the RDAs for these nutrients are already linked to energy and protein intakes. Thus, ideally dietary intakes of these vitamins by active individuals should be adequate unless dietary food choices are poor or energy intake is restricted. No extensive research has been done on whether nutrient requirements are higher in active individuals with chronic diseases, energy restriction, musculoskeletal injuries, or individuals under high stress.



References


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