Prior to the study, there was limited evidence regarding the link between B vitamin supplementation and improved endothelial function through lowered plasma homocysteine levels.
Based on this, researchers at Japan’s Ehime University, Osaka University, Dokkyo Medical University and Fukushima Medical University, as well as Egypt’s Minia University, conducted an RCT to determine if low-dose B vitamin supplementation could enhance endothelial function in Japanese adults who had one or more components of metabolic syndrome.
There’s a B in my beverage
The trial — which did not have a washout period or subject blinding — involved 127 Japanese men and women aged 40 to 65, each with at least one component of metabolic syndrome. They were also not taking any medication for their condition.
For two months, they were given a supplement in the form of a beverage, which contained B vitamins, as well as vitamins C, D and E
They were then divided into an early intervention and a later intervention group. The researchers measured their flow-mediated dilation, plasma homocysteine levels, serum B vitamins, and vitamin C levels.
Subsequently, the researchers reported a significant rise in serum B vitamins and vitamin C levels, along with a reduction in plasma homocysteine levels.
They wrote: “The mean serum homocysteine level pre- and post-intervention was 9.8µmol/L and 8.2µmol/L in the early intervention group and 10.8µmol/L and 7.4µmol/L in the later intervention group. However, no significant changes in flow-mediated dilatation was found.”
They added that past research had found the effects of multi-vitamin supplementation on heart disease risk factors ‘controversial’: therapies using only vitamin C or both vitamin C and vitamin E were said to have prevented acute impairment in endothelial function.
Furthermore, long-term vitamin C supplementation has been linked to improvement in flow-mediated dilation in patients with coronary artery disease.
However, the researchers also referred to a recent systematic review and meta-analysis of 16 RCTs and “found no effect of vitamin D on endothelial function, and two large-scale trials could not find any association between vitamin C and E supplements and major cardiovascular outcomes”.
They added that unfavourable interactions between folate and vitamins C and E could modify the impact of B vitamin supplementation; one study had reported significantly improved endothelial function when either vitamin C or vitamin E alone were used.
Co-administration of both vitamins, on the other hand, was found to be ineffective. They also noted that at each examination, most of the current study’s participants had not sufficiently fasted, so their serum triglyceride levels were likely to be higher, making it especially important to interpret the results carefully.
Levels and limitations
The researchers acknowledged that the in vivo interaction of combined supplementation could not be confirmed, as the sole effect of each of the B vitamins, as well as vitamins C or E, had not been assessed.
Additionally, since they had not included a washout period in the study, thus leading to a carryover effect on serum vitamins B6 and B12, folate and vitamin C (though there was no such effect on the participants’ plasma homocysteine levels).
The researchers further noted that the study subjects’ mean dietary intakes of vitamins B6, and B12, folate and vitamin C, when assessed at two and four months, were “similar to those at baseline for both the early and later intervention groups (data were not shown)”.
They then concluded: “Dietary intakes of these vitamins during the study period were unlikely to be affected by the intervention.
“Among subjects with one or more components of metabolic syndrome, low-dose multivitamin supplementation, including B vitamins, was associated with a significant reduction in plasma homocysteine levels, but not with flow-mediated dilation.”
Source: Journal of Clinical Biochemistry and Nutrition
“Association between vitamin B group supplementation with changes in % flow-mediated dilatation and plasma homocysteine levels: a randomized controlled trial”
Authors: Koutatsu Maruyama, et al.