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explained by the rapid decline in absorption that occurs at intakes above 5 mg (Hayes and Hegsted, 1973; SCOGS/LSRO, 1978) and the rapid urinary excretion of thiamin (Davis et al., 1984; McAlpine and Hills, 1941; Najjar and Holt, 1940).

Dose-Response Assessment

In the absence of known toxic effects by ingestion, a lowest-observedadverse-effect level (LOAEL) and an associated no-observed-adverseeffect level (NOAEL) cannot be determined. Supplements that contain up to 50 mg/day of thiamin are widely available without prescription, but effects of this level or more of intake do not appear to have been studied systematically.

Intake Assessment

Although no UL can be set for thiamin, an exposure assessment is provided here for possible future use. Based on data from the Third National Health and Nutrition Examination Survey, the highest mean intake of thiamin from diet and supplements for any life stage or gender group was reported for men aged 31 through 50 years: 6.7 mg/day. The highest reported intake at the ninety-fifth percentile was 11.0 mg/day in women aged 51 years and older (see Appendix H).

Risk Characterization

Although no adverse effects have been associated with excess intake of thiamin from food or supplements, this does not mean that there is no potential for adverse effects resulting from high intakes. Because data on the adverse effects of thiamin intake are extremely limited, caution may be warranted.

RESEARCH RECOMMENDATIONS FOR THIAMIN

Priority should be given to studies useful for setting Estimated Average Requirements (EARs) for thiamin for children, adolescents, pregnant and lactating women, and the elderly. Future studies should be designed around the EAR paradigm, use graded levels of thiamin intake with clearly defined cutoff values for clinical adequacy and inadequacy, and be conducted for a sufficient duration. To do this, close attention should be given to the identification of indicators on which to base thiamin requirements.



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