The B vitamins are needed for energy production because they are required as cofactors in a number of key enzymes in glycolysis and the citric acid cycle such as pyruvate carboxylase (biotin), pyruvate dehydrogenase (riboflavin and thiamine) and α-ketoglutarate dehydrogenase (riboflavin and thiamine). In addition, the electron carriers NAD+ and FAD require niacin and riboflavin, respectively. Because nerves have a high requirement for energy, the B vitamins play an important role in nerve function. In addition, pyridoxal phosphate (vitamin B6) is required as a co-factor for tryptophan decarboxylase which catalyses the conversation of 5-hydroxytryptophan to serotonin. The high concentration of neurones in the CNS, and the use of serotonin as an important neurotransmitter, suggest that B vitamins may play a role in mood regulation. In fact, some B vitamins have been shown to be inversely related to depressive symptoms when measured in the plasma.
For example, researchers1 have investigated the relationship between dietary vitamin B6, plasma pyridoxal 5’-phosphate and depressive symptoms in 618 Hispanic and 251 white elderly subjects. The Hispanic subjects had lower vitamin B6 intakes when compared to whites, but their plasma pyridoxal 5’-phosphate levels were not significantly different. Plasma pyridoxal 5’-phosphate was significantly inversely associated with the Centre for Epidemiological Studies Depressive Scale definition of depressive symptoms. Levels of pyridoxal 5’-phosphate below 20nmol/L, a levels that would be classed as deficient, typically doubled the risk of depression. Total intakes of vitamin B6 (diet plus supplements) were not associated with depression, but dietary vitamin B6 was significantly associated with depression. This suggests that the cause and effect between vitamin B6 and depression is not straight forward and may involve confounding variables, evidence supported by the lack of effect of B6 supplements in depressed patients in some studies.
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