Vitamin B₁

The chemical name of vitamin B₁ is thiamine. The Dietary Reference Intakes for Japanese has set the amount of thiamine hydrochloride. Vitamin B₁ is involved in glucose metabolism and branch amino acid metabolism, the deficiency of vitamin B₁ causes beriberi and Wernicke-Korsakoff syndrome. The excess of vitamin B₁ causes headache, irritation, insomnia, rapid pulse, weakened, contact dermatitis and itching.

Vitamin B₁ in food is present bound to the enzyme protein as thiamine diphosphate (TDP). As foods is cooked and processed and enzyme protein is released from most of TDP with gastric acid, TDP is hydrolyzed in the digestive tract to thiamine and absorbed in the small intestine. The relative bioavailability of vitamin B₁ has been reported 60%​​..

In adult and child, the required amount of vitamin B₁ has been determined from the inflection point in the relationship between the urinary excretion and intake. In general, water soluble vitamins more than the required amount are excreted into the urine. The intake of vitamin B₁ that increases to excrete into the urine has been determined the Estimated Average Requirement of vitamin B₁. In the meta-analysis that has been reported in 18 countries, the inflection point is 0.35 mg/1,000 kcal as thiamine and 0.45 mg/1,000 kcal as thiamine hydrochloride. The point of value has been set to　the reference value of the Estimated Average Requirement calculation of 1-69 years of age group, multiplied by Estimated Energy Requirement and determined Estimated Average Requirement. The recommended amount has been determined by multiplying the Estimated Average Requirement by Recommended Amount calculation coefficient 1.2.

Because energy requirements during pregnancy varies with each individual and the metabolism is enhanced, the additional amount 0.2 mg/d has been applied to the first trimester pregnancy and the second trimester pregnancy.

For the additional amount of lactation, the approximate amount has been set to 0.169 mg/d, with multiplying concentration in human milk 0.13 mg/L by milk yield 0.78 L/d and dividing by the relative bioavailability 60 % and rounded to 0.2 mg/d.

In 0-5 months infant, the approximate amount has been set to 0.10 mg/d by multiplying the concentration of human milk 0.13 mg/L by standard mammals amount 0.78 L/d. In 6-11 months infant, the approximate amount has been set to the rounded average between the extrapolated value of 0-5 months infant and the extrapolated amount of adult.

　Although there are some reports of clinical symptoms with high intake of thiamine, it is insufficient to set the upper limit, therefore the upper limit has not been set.

References: br>
The Dietary Reference Intakes for Japanese (2015 edition) Water Soluble Vitamin (pdf) br>
The Dietary Reference Intakes for Japanese (2010 edition) Vitamin B₁ (pdf)