‘Subtle changes’
ANOVA analyses revealed a “highly significant” reduction in anxiety at post test (F[1,173] = 10.03; P = .002; np 2 = .055), driven primarily by reduced anxiety in the B6 group (t[88] = 3.51; P < .001; d = .37). The placebo group also showed some reduction in anxiety, but it was not deemed significant, and the overall interaction itself did not reach significance.
A comparison of the B12 group with the group that received placebo revealed a significant reduction in anxiety at post test (F[1,175] = 4.08; P = .045; np 2 = .023), similarly driven by reduced anxiety in the B12 group (t[89] = 1.84; P = .069; d = .19) – but the interaction was not significant.
Among the B6 group, there was a highly significant reduction in scores on the generalized anxiety disorder and social anxiety subscales of the SCAARED, and there was a trend toward reductions on the other subscales. Among the B12 group, there was a significant reduction only on scores on the separation anxiety subscale. No significant changes were found in the placebo group.
The ANOVA test analysis of the B6 and placebo group data showed “no uniform direction of change” in depression at post test. The researchers found a “tendency” for depression scores to decrease between baseline and post test in the B6 group but to increase in the placebo group – an interaction that “approached” significance (F[1,96] = 3.08; P = .083; np 2 = .031), they report.
The ANOVA analysis of the B12 and placebo group data revealed no significant or trending effects, and the t-test comparing baseline and post-test scores in the B12 group was similarly nonsignificant.
B6 supplementation did change visual contrast thresholds, but only when a suppressive surround was present. There were “no clear effects” of B6 supplementation on other outcome measures, including binocular rivalry reversal rate and the tactile test battery, the investigators note.
“We found that supplementation with B6 produced subtle changes in tests of visual processing in a way that suggested an increase in the level of the inhibitory neurotransmitter GABA,” Dr. Field reported.
Vitamin B6 is a “cofactor for a metabolic pathway in the brain that converts the excitatory neurotransmitter glutamate into the inhibitory/calming GABA,” he said.
“By increasing the quantity of the cofactor, we slightly speed up the rate of this metabolic process, and so you end up with a bit more of the GABA neurotransmitter and a bit less glutamate. The net effect of this is to slightly reduce the amount of activity in the brain,” Dr. Field added.
Most common nutrient deficiency
Carol Johnston, PhD, professor and associate dean for faculty success, College of Health Solutions, Arizona State University, Phoenix, said vitamin B6 is “the most common nutrient deficiency in the United States;” 16% of men and 32% of women are reportedly B6 deficient.
“Young women on birth control are at higher risk for B6 deficiency due to effects of oral contraceptives on B6 metabolism,” whereas vitamin B12 deficiency is more common in older adults, said Dr. Johnston, who was not involved with the study.
The current study’s population mainly consisted of young women, and the interpretation of the data is “limited” because the researchers did not measure blood status for B6 and B12, Dr. Johnston noted. It is possible the sample was low in B6 and that the supplements “improved cognitive measures.”
Because the population was young – no one was older than 60 years – B12 status was likely “adequate in the sample, and supplementation did not have an impact,” she said.
Overall, Dr. Johnston cautioned that it is important to “alert clinicians and the general public about the concerns of overdosing B6.” For example, supplementation at high amounts can cause potentially irreversible sensory neuropathy, she noted.
“The safe upper limit defined by experts is 100 mg per day – the dosage used in this trial. Daily supplementation should not exceed this level,” Dr. Johnston said.
The vitamin tablets used in the study were supplied by Innopure. The investigators and Dr. Johnston have reported no relevant financial relationships.
A version of this article first appeared on Medscape.com.