The synthesis of pentoses is important when considering the hexomonophosphate shunt. This is a pathway where sugars of various carbon lengths are interconverted and NADPH is produced. Pentoses are also used in the production of nucleic acids, whereas NADPH is needed for the synthesis of fatty acids. Furthermore, thiamin is needed for membrane and nerve conduction; however, it is not clear how thiamin functions in regard to nerve conduction.

Sources

Thiamin is widely distributed in foods. Good sources of thiamin are whole grain products, enriched wheat, lean pork, yeast, liver, and nuts. Naturally occurring anti-thiamin factors are present in raw fish but are negated by cooking fish. Thus, these factors are thermolabile. Other foods that contain anti-thiamin factors are tannic and caffeic acids; these are thermostabile and found in coffee, tea, betel nuts, blueberries, black currants, brussel sprouts, and red cabbage. Thiamin destruction can be prevented or reduced if the offending agent is eaten with a food containing vitamin C or citric acid .

Governmental Recommended Intake

0.5 mg/1000 calories or no less than 1 mg per day. Dietary supplements often contain more than this amount.

Deficiency symptoms

Deficiency is rare. It can occur with long-term extremely low intake or high alcohol intake. The first symptom of deficiency is loss of appetite, progressing to cardiac hypertrophy or dysrhythmia, and neurologic symptoms due to alcoholism (Wernicke's encephalopathy/Wernicke-Korsakoff syndrome). Beriberi (dry, wet, or acute) is a common deficiency identified in older adults.

Human Studies

To date, studies indicate that athletes' intake of thiamin appears to be adequate. However, evidence for an ergogenic effect of thiamin is equivocal. Knippel et al. found that supplementation of 900 mg/day for 3 days enabled trained cyclists to achieve lower blood lactate and heart rate levels during intense exercise. This increase in the lactate threshold was significant. The mechanism for this improvement can be understood because thiamin is one of the cofactors serving as part of the pyruvate dehydrogenase complex (PDHC). PDHC drives the forward reaction of pyruvate to acetyl CoA to produce energy through the Krebs cycle. Theoretically, if less pyruvate is needed for the acetyl CoA product, more may be available for the glucosealanine cycle and thus less lactate is produced during intense exercise. Studies conducted with pyruvate alone illustrate a possible buffering capacity. However, the current study mentioned above has yet to be replicated.

One could surmise that the need for thiamin might be increased in athletes due to their greater demand for carbohydrates or energy during prolonged endurance events. Because research with pyruvate and dihydroxyacetone (DHA) has shown the benefit for enhancing endurance exercise, future research should examine if a synergy or potentiation of ergogenics can occur by adding thiamin to exogenous pyruvate during intense exercise.

Safety and Toxicity

Toxicity has rarely been seen (with doses as high as 500 times the recommended daily intake)