Vitamin B12 is critical for the function of the nervous system, so it’s natural to wonder if it plays a role in mental illness like anxiety or depression.
But anxiety is tough to study, because you can’t do interventional studies in most cases. Instead, most research focuses on observational studies to find correlations, which has limitations.
I’m going to summarize the several studies on vitamin B12 deficiency and anxiety that I’ve read in this short post. If you just want a short answer, I’ve basically seen that:
- Vitamin B12 deficiency doesn’t directly cause anxiety
- However, a vitamin B12 deficiency can lead to high serum levels of homocysteine, which is highly linked to both anxiety and depression.
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Research on Vitamin B12 Deficiency and Anxiety
Most high quality studies on this topic show either no or minimal effect of vitamin B12 levels and anxiety after controlling for variables (e.g. age, gender, etc.).
A 2019 review identified 18 high quality studies and had 2 major findings (1):
- Vitamin B12 had a positive effect on overall mood in 11 of the 18 articles compared to a placebo group.
- There was no statistically significant effect on depression or anxiety, even though there was a very small benefit.
There may be some cases, where a B12 supplement does in fact help anxiety, but for the average person with an anxiety disorder, it likely won’t do much. Although it’s not likely to make it worse either.
The few studies that do show some benefit are either weaker studies, or done in very specific populations. For example:
- A study in men with HIV found an association between low vitamin B12 levels and anxiety (2).
- A cross-sectional analysis found that low vitamin B12 intake was correlated with depression, but only in women (3).
Current research makes a pretty strong case that a typical vitamin B12 deficiency does not cause anxiety or depression, at least not directly.
Research on High Levels of Homocysteine and Anxiety
Here’s where things get interesting…
Some studies have measured more than just vitamin B12 and folate, like homocysteine levels.
And multiple studies have found that while folate and B12 haven’t correlated with anxiety disorders, excess homocysteine (aka hyperhomocysteinemia) does.
Here’s a summary of a few of those:
- Hyperhomocysteinemia was associated with about a 300% increased risk for depression, and 600% increased risk for generalized anxiety disorder (4).
- An analysis of data from a cohort of middle aged and elderly men found that hyperhomocysteinemia resulted in a 90% increased risk of depression (5).
How is Vitamin B12 Related to Homocysteine?
Folate (B9), vitamin B12, and homocysteine are all highly related.
Both vitamins B9 and B12 are needed to break down homocysteine (6). If someone has a low intake of vitamin B12 or B9 over the long term, it can lead to hyperhomocysteinemia.
In theory, if hyperhomocysteinemia causes anxiety or depression, then so should a vitamin B9 or B12 deficiency.
But that’s not what the research shows…why not?
Even with a low intake of vitamin B12, it takes a long time for a deficiency to develop, and a relatively long time for the consequences to develop like hyperhomocysteinemia.
So if someone just meets the condition of having low B12 levels, it may not have been long enough for homocysteine to rise to a dangerous amount.
Obviously more research will be needed, but my theory would be that if you only looked at subjects with a large and chronic B12 deficiency, you would find a correlation to anxiety and depression as well.
Vitamin B12 is needed to break down the amino acid homocysteine, so a B12 deficiency often results in excess homocysteine.
Summary: Could a Vitamin B12 Deficiency Cause Anxiety?
Having a small vitamin B12 deficiency by itself doesn’t appear to be a significant risk factor for anxiety or depression.
However, a long-term B12 deficiency can have an impact on other substances like homocysteine, which is in fact linked to a much higher risk of anxiety and depression when serum levels are too high (hyperhomocysteinemia).
So while more research is needed, it’s possible that a long-term vitamin B12 deficiency could increase the risk of anxiety, whether directly or indirectly.