Thiamin is a water-soluble vitamin. The active variety is a phosphorylated form called thlarnin pyrophosphate, which functions in carbohydrate metabolism to help convert pyruvate to acetyl coenzyme A for entry to the Krebs cycle and subsequent steps to generate ATP. Thiamin also functions in maintaining the health of the nervous system and the heart muscle. Food sources include nuts, liver, brewer’s yeast, and pork. Dietary supplements containing thiamin are frequently marketed with claims of increased energy production, maintenance of memory, and improved carbohydrate tolerance.

Because exercise and stress can tax the metabolic pathways that depend on thiamin and riboflavin, it is logical that the requirements for these vitamins maybe increased in athletes, active people, and persons exposed to acute or chronic stressors. In these groups, marginally low intakes of thiarnin and riboflavin can be corrected easily and safely by supplements containing the recommended dietary allowance (RDA) of these nutrients; for such purposes, a balanced multivitamin is the best approach.

The term B complex simply refers to a mixture or combination of the eight essential B vitamins: thiamin (Bt), riboflavin (B2), niacin (B3), pyridoxine (B6), pantothenic acid, folic acid, cyanocobalamin (B12), and biotin. Most of the B vitamins play a critical role as cofactors in cellular energy metabolism. Cofactors can be thought of as “helper nutrients” that assist chemical reactions. For example, the process of glycolysis, which converts energy stored as glycogen into glucose molecules, requires vitamin B6 and biotin. The conversion of pyruvate (a metabolite of glucose) to acetyl coenzyme A (the first step in the Krebs cycle in energy metabolism) requires pantothenic acid, and further metabolism requires biotin, riboflavin, and niacin. Lack of any of the B vitamins can cause fatigue and lethargy, which is why B-complex supplements are often promoted as “energy boosters” and “stress formulas.”

Because of thiamin’s role in carbohydrate metabolism and nerve function, supplements have been promoted for increasing energy and maintaining memory. It is well known that thiamin deficiency (beriberi) is associated with generalized muscle weakness and mental confusion. Although beriberi is rare in industrialized countries, there continue to be reports of the condition in the medical literature. For example, thiamin insufficiency has been reported in Chinese prisoners (Chen et al., 2003), surgical patients (Nakasaki et al,, 1997), rural Cubans (Marcais-Matos et al., 1995), Gambian children (Bates et al., 1987), alcoholics (Walden-lind et al., 1981), and older women (Wouters-Wesseling et al., 2002). In addition to these populations, which may be “expected” to have deficient thiamin intakes, other populations that have been shown to have marginal or suboptimal thiamin intake include female collegiate volleyball players (Papadopoulou et al., 2002), collegiate wrestlers (Williams, 1989), and other athletes who may be restricting energy and/or food intake (Manore, 2000; van der Beek et al., 1994). Luckily, inad-equate thiamin status is easily and rapidly corrected by thiamin supplements in the range of 50-100 mg/day (Descombesetal., 2000; Nakasaki et al., 1997; Powers et al., 1985; Waldenlind et al., 1981).

Thiamin appears to be involved in the release of acetylcholine, a neurotransmitter, from nerve cells a fact that may account for isolated studies showing thiamin supplementation to benefit cognitive functioning (Benton et al., 1995). As a coenzyme for carbohydrate and branched-chain amino acid metabolism, thiamin has been touted as both a performance and an energy supplement, but supplementation studies of subjects already at normal thiamin status have not shown a beneficial effect. Because dietary thiamin requirements are based on caloric intake, people who consume more calories, such as athletes, are likely to require higher-than-average intakes of thiamin to help process the extra carbohydrates into energy. In persons who consume “whole” forms of carbohydrates, intakes of thiamin and other B vitamins will increase along with carbohydrate intake.

During acute periods of stress, including exercise, thiamin needs may be temporarily elevated, but outright thiamin deficiencies are rare except in persons consuming a severely restricted diet. On the basis of metabolic studies (Manore, 2000), there is biochemical evidence that riboflavin and/or thiamin status is poorer in persons who exercise moderately (2~ 5 hours/week) and who diet (restrict their food intake for weight loss).

Suboptimal dietary intakes of thiamin, riboflavin, vitamin B6, and vitamin C are known to compromise physical performance with reductions in mitochondrial metabolism and aerobic power (van der Beek et al., 1994). In one study, subjects consuming a diet low in thiamin and riboflavin (55% of RDA for 11 weeks) showed 7-11% reductions in oxygen uptake and power output (van der Beek et al., 1994). Exercise has also been shown lo compromise riboflavin status an effect that may be compounded and more severely affect performance when dietary intake is marginal (Soares et al., 1993; Winters et al., 1992).

No adverse side effects are known with thiamin intakes at RDA levels or even at levels several times the RDA. The daily value (DV) for thiamin is 1.5 mg (RDA is 1.2 mg/day for men, LI mg/day for women). The Food and Nutrition Hoard (FNB) has not established an upper-limit intake level for thiamin, but a level of 50 mg has been established by the Council for Responsible Nutrition as the NOAF.L (no observed adverse effect level). Virtually every multivitamin contains thiamin at 100% DV levels (1.5 mg) or higher. Isolated supplements of thiamin are not necessary.

When it comes to defining optimal amounts of vitamins and minerals, confusion is more the rule than the exception. Before 1997, the benchmark of nutritional adequacy was the RDA, established by the I7NB, which is part of the National Academy of Sciences. In general, the RDAs have always been viewed (as judged by the FNB) “to be adequate to meet the known nutrient needs of practically all healthy persons.” Because scientific knowledge regarding the roles of nutrients, and their role in health and disease, has expanded dramatically since the inception of the RDAs, a new set of terminology dietary reference intakes (DRIs) has been established. The DRIs are based on contemporary scientific studies related to the role of nutrients in reducing the risk of osteoporosis, cancer, cardiovascular disease, and other chronic conditions. DRI is a generic term used to refer to the following reference values:

Estimated average requirement (EAR): the intake value that meets the nutrient requirements of 50% of an age and gender-specific population.

Recommended dietary allowance (RDA): the intake value that meets the nutrient requirements of nearly all people in an age- and gender-specific group.

Upper intake (UL): maximum intake of a specific nutrient that is unlikely to pose health risks.

Adequate intake (Al): suggested levels of nutrient intake that are established when insufficient data exist to establish a true RDA.

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