itamins are needed in the diet because they cannot be synthesised endogenously but are required for vital metabolic functions. Most vitamins serve as co-factors to enzymes in metabolic pathways, but some are required for other physiological roles such as reducing agents. A deficiency of any of the vitamins can cause a specific disease, which if left untreated will eventually result in death. However, a chronic low intake of any of the vitamins can cause sub-clinical deficiencies which are difficult to diagnose because they produce vague symptoms that can increase and decrease in severity depending on the intake of the vitamin and the temporal requirement for that vitamin. While a deficiency will ultimately result in death, a sub-clinical deficiency, also called an insufficiency, will likely result in long-term ill heath. Insufficiencies of vitamins can therefore seriously effect physical performance.
Researchers have assessed the effects of short-term vitamin insufficiencies on healthy individuals. For example, in one study1, healthy male subjects were fed diets deliberately restrictive in thiamine, riboflavin, vitamin B6 and vitamin C, but which contained adequate intakes of the other known vitamins and minerals. The restriction of the vitamins selected was only to 32.5 % of the Dutch recommended intake, and as such would likely have caused ill health if the diet was continued long term. The erythrocyte enzyme activity, blood levels and urinary excretion of the four vitamins decreased in all the subjects suggesting that the diet was providing an inadequate intake. While no ill health was reported in the subjects and physical performance was generally unaffected, the subjects did experience a reduction in aerobic performance and deterioration in the blood lactate accumulation time of onset.
These results therefore support the hypothesis that sub-clinical deficiencies can be present in individuals and cause apparently no ill health, but have subtle physiological effects that are difficult to determine. In particular, these insufficiencies may first become apparent by a deterioration in physical ability when close to the limit of performance. If the insufficiency continues, more noticeable symptoms may appear. Evidence from nutritional research papers that have investigated vitamin and mineral intakes of supposedly healthy humans have shown that a high percentage of individuals from Western nations have inadequate micronutrient intakes. It is likely that many of these individuals have changes to their physiology that result from decreased flux through certain metabolic pathways, due to inadequate co-factor activity. However it is unlikely they will be aware of their problem.
RdB
