Plain language summary
Research suggests that vitamin B12 may possess antioxidant properties (i.e. they neutralise free radicals that can cause damage to cells or ‘oxidative stress’). The triage theory suggests that nutrients may be reallocated to necessary functions for survival if there is not enough for all processes. As such, lower than optimum levels of B12 may contribute to oxidative stress and free radicals which may relate to age-related disease development. This systematic review explores if low vitamin B12 is related to increased oxidative stress. The systematic review included 15 articles and found evidence to suggest there is a relationship between lower vitamin B12, low antioxidant status and oxidative stress. However, there is a lack of robust studies (in the form of randomised controlled trials and prospective studies) in humans suggesting that further research is needed to establish cause and effect.
Abstract
The triage theory posits that modest micronutrient deficiencies may induce reallocation of nutrients to processes necessary for immediate survival at the expense of long-term health. Neglected processes could in time contribute to the onset of age-related diseases, in which oxidative stress is believed to be a major factor. Vitamin B12 (B12) appears to possess antioxidant properties. This review aims to summarise the potential antioxidant mechanisms of B12 and investigate B12 status in relation to oxidative stress markers. A systematic query-based search of PubMed was performed to identify eligible publications. The potential antioxidant properties of B12 include: (1) direct scavenging of reactive oxygen species (ROS), particularly superoxide; (2) indirect stimulation of ROS scavenging by preservation of glutathione; (3) modulation of cytokine and growth factor production to offer protection from immune response-induced oxidative stress; (4) reduction of homocysteine-induced oxidative stress; and (5) reduction of oxidative stress caused by advanced glycation end products. Some evidence appears to suggest that lower B12 status is related to increased pro-oxidant and decreased antioxidant status, both overall and for subclinically deficient individuals compared to those with normal B12 status. However, there is a lack of randomised controlled trials and prospective studies focusing specifically on the relation between B12 and oxidative stress in humans, resulting in a low strength of evidence. Further work is warranted.
Methodological quality
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