Thiamin, riboflavin and vitamin B6: impact of restricted intake on physical performance in man.

OBJECTIVE: A combined marginally deficient status of thiamin, riboflavin, vitamin B6 and vitamin C may affect physical performance, but the relative contribution of each vitamin can only be speculated. In a previous study we did not find any effect of restricted intake of vitamin C individually. Therefore, the functional effect of restriction of thiamin, riboflavin or vitamin B6, individually or in conjunction, was investigated. METHODS: A double-blind, 2 x 2 x 2 complete factorial experiment on the effects of thiamin, riboflavin and vitamin B6 restriction on physical performance was executed with 24 healthy men. During 11 weeks of low vitamin intake, the subjects were given a daily diet of regular food products providing no more than 55% of the Dutch Recommended Dietary Allowances (RDA) for thiamin, riboflavin and vitamin B6. Other vitamins were supplemented at twice the RDA level. RESULTS: In vitamin-restricted subjects, blood vitamin levels, erythrocytic enzyme activities and urinary vitamin excretion decreased and in vitro erythrocytic enzyme stimulation increased. Short-time vitamin restriction had no harmful effects on health. A significant overall decrease was observed in aerobic power (VO2-max; 11.6%), onset of blood lactate accumulation (OBLA; 7.0%) and oxygen consumption at this power output (VO2-OBLA; 12.0%), peak power (9.3%), mean power (6.9%) and related variables (p < 0.01). However, the observed performance decrements could not be attributed to marginal deficiency for any of the vitamins studied. CONCLUSION: The absence of vitamin-specific effects on performance decrements due to thiamin, riboflavin and vitamin B6 restriction suggests quantitatively similar but non-additive effects of these B-vitamins on mitochondrial metabolism.