THIAMIN, RIBOFLAVIN AND VITAMIN-B-6 - IMPACT OF RESTRICTED INTAKE ON PHYSICAL PERFORMANCE IN MAN

Objective: A combined marginally deficient status of thiamin, riboflav in, vitamin B-6 and vitamin C may affect physical performance, but the relative contribution of each vitamin can only be speculated. In a pr evious study we did not find any effect of restricted intake of vitami n C individually. Therefore, the functional effect of restriction of t hiamin, riboflavin or vitamin B-6, individually or in conjunction, was investigated. Methods: A double-blind, 2 x 2 x 2 complete factorial e xperiment on the effects of thiamin, riboflavin and vitamin B-6 restri ction 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 Recom mended Dietary Allowances (RDA) for thiamin, riboflavin and vitamin B- 6. Other vitamins were supplemented at twice the RDA level. Results: I n vitamin-restricted subjects, blood vitamin levels, erythrocytic enzy me activities and urinary vitamin excretion decreased and in vitro ery throcytic 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 acc umulation (OBLA; 7.0%) and oxygen consumption at this power output (VO 2-OBLA; 12.0%), peak power (9.3%), mean power (6.9%) and related varia bles (p < 0.01). However, the observed performance decrements could no t be attributed to marginal deficiency for any of the vitamins studied . Conclusion: The absence of vitamin-specific effects on performance d ecrements due to thiamin, riboflavin and vitamin B-6 restriction sugge sts quantitatively similar but non-additive effects of these B-vitamin s on mitochondrial metabolism.