Optimal B12 Levels For Females: Full Explanation (2024)

What are the optimal B12 levels for females?

Before we give specific numbers, we should mention that yes, women do have different average B12 levels than men. One Nepalese study found slightly higher median levels in females. Another study, from Czechia, also found higher levels in females, although the differences were only of a borderline statistical significance. Third time’s a charm, so here’s another one, by Israeli researchers, who found a similar trend:

In all, 7,963 individuals met the inclusion criteria. Serum vitamin B12 mean levels were 312.36 and 284.31 pmol/L for women and men respectively (p < 0.001). Deficiency prevalence was greater for men (25.5%) in comparison with women (18.9%; p < 0.001). Men were strongly associated with severe deficiency.

Vitamin B12 Deficiency and the Role of Gender

The Optimal B12 Levels For Females

Now, for the interesting part:

Determining optimal B12 levels for women can be challenging, because the traditional blood test doesn’t provide a complete picture of functional B12 levels. As explained in our article about optimal B12 levels, the test suffers from a couple of limitations:

  • Your body can only use “active B12” (holoTC), not the inactive analogues (holoHC). However, the regular B12 blood test doesn’t distinguish between the two. In fact, inactive analogues of B12 may representas much as 90%of your total-B12 blood levels. Only an active-B12 test can discover your true, functional B12 levels.
  • That being said, there is a positive correlation between active-B12 levels and total-B12 levels. But they tend to agree at the extremes – either the very-low or the very-high. However, most people exist in the middle, and so up to 50% of the population will have total-B12 levels above the 150pmol/L cut-off, but with low active-B12 levels. Therefore, if you rely on the regular blood test, you may think that your levels are fine, even though an active-B12 test may reveal a legit B12 deficiency.
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The solution?

Test For Active-B12 Levels

First, if you can find a place that does the active-B12 test, go for it. When it comes to B12 deficiency tests, this is as accurate as it gets. The numbers you should be aiming for:

Optimal B12 Levels For Females: Full Explanation (2)

Unfortunately, you’re not likely to find active-B12 tests in regular hospitals.


Aim Higher, Just In Case

As a workaround, aim for total-B12 levels of at least 500-550, which has been shown to be a good indicator of sufficient active-B12 levels in most cases.

Again, most people exist on the middle of the normal B12 level range. At these levels, you’ll find patients with both low and high active-B12 levels. This is why the normal test misses out on so many patients with a true underlying B12 deficiency.

Look at this graph:

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The red dots on the left side show patients with total-B12 levels of 150pmol/L or less. In many countries, this is the cut-off for B12 deficiency. The red dots on the right side show levels of 301pmol/L or higher, where doctors would normally rule out a deficiency.

However, notice the concentration of gray dots in the middle (314 out of 468 patients, exactly two-thirds). We didn’t color them gray for no reason. We call this range the gray-zone. The patients in bold gray are those with low levels of active-B12 (meaning, they have a B12 deficiency). The light gray ones have sufficient levels of active-B12.

This easily shows you why the regular blood-test is so problematic. But, you can also see how aiming for total-B12 levels of 500-550 or more is a good insurance policy for ensuring sufficient active-B12 levels. True deficiencies aren’t common at these levels, but they do exist. We like Sally Pacholok’s suggested B12 level chart in Could It Be B12?:

B12 StatusB12 Levels(pg/ml)
Deficiency< 550
Normal> 550
Healthy nervous system & disease prevention in the elderly> 1000

At this time, we believe normal serum B12 levels should be greater than 550 pg/ml. For brain and nervous system health and prevention of disease in older adults, serum B12 levels should be maintained near or above 1000 pg/ml.

Sally M. Pacholok & Jeffrey J. Stuart, “Could It Be B12?

Of course, many people with B12 levels of 300, 400, or 500 do not have a B12 deficiency (as measured by active-B12 levels, and as you saw in the graph prior). However, you can’t overdose on B12, so there’s no risk in aiming higher. It makes sense to set the bar higher, because it can prevent a lot of B12 deficiencies that would otherwise be dismissed.

So, what are the optimal B12 levels for women? If you’re unable to find an active-B12 test, just aim for total-B12 levels of 550 or higher. This applies to men as well.

Look At The Clinical Picture

It’s important to consider the clinical picture when assessing B12 levels. If you exhibit signs of B12 deficiency or pernicious anemia despite normal or high blood levels, start B12 supplementation immediately. B12 deficiency can lead to severe neurological symptoms, and early intervention is crucial. Here’s what NEQAS has to say:

In the event of any discordance between clinical findings of B12 deficiency and a normal B12 laboratory result, then treatment should not be delayed. Clinical findings might include possible pernicious anaemia or neuropathy including subacute combined degeneration of the cord. We recommend storing serum for further analysis including MMA, or holotranscobalamin and intrinsic factor antibody analysis, and treating the patient immediately with parenteral B12 treatment.


So, do you show clear signs of B12 deficiency or pernicious anemia? Then ignore blood numbers and start a B12 shots therapy immediately. You can even do it at home.

Remember,you can’t overdose on B12. There’s no risk in supplementing, even if you don’t have a B12 deficiency. However, if you are deficient, the risk in leaving it untreated is enormous. The myelin around your nerves gradually strips off, and before long, all kinds of neurological symptoms appear. You want to avoid this stage of B12 deficiency at all costs, where the window of opportunity for effective intervention is very short.

Optimal B12 Levels In Pregnancy

Pregnancy brings unique challenges in maintaining optimal B12 levels for females, as B12 deficiency can cause developmental issues in the baby. And there are physiological changes that affect the normal range of vitamin B12 in pregnancy:

One paperreported low B12 levels being present in up to 28% of normal pregnancies. Another studyfound that almost 35% of first-trimester pregnancies show B12 levels below 150pmol/L despite adequate B12 consumption. However, despite these findings, there were no visible signs of B12 deficiency. So, what gives?

The authors found that while B12 levels tend to drop naturally during pregnancy, this decrease is primarily due to a reduction in inactive B12 levels. They concluded that these are normal physiological changes during pregnancy:

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Another study foundan almost 50% decrease in total-B12 levels in late pregnancy among healthy, pregnant Danish women. The drop in B12 levels reversed after giving birth, and was not reflected in active-B12 levels (holoTC). Here again, it was due to declining levels of haptocorrin-bound B12, or inactive analogues of B12 (holoHC):

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As you can see, the traditional B12 blood test makes things complicated, even more so in pregnancy. But ensuring optimal B12 levels for females is especially important during pregnancy, because this way we can protect babies from developmental issues. This is double as true when she then breastfeeds.If we can diagnose B12 deficiency early enough in a mother, we can prevent it in her baby.

So, on one hand, we recommend to shoot for levels around the 500 mark or higher. On the other hand, we’re telling you that it’s normal for B12 levels to drop significantly during pregnancy. To solve this riddle and ensure optimal B12 levels during pregnancy, supplement daily with B12, preferably in a high-quality form like methylcobalamin.

By the way, if you know you need B12 shots and your doctors won’t prescribe enough of them, you can get injectable methyl-B12 from us (prescription-free):

Order Injectable Methylcobalamin B12

Optimal B12 Levels For Women: Summary

In conclusion, to maintain optimal B12 levels for females:

  • The regular vitamin B12 blood test is not accurate, because it doesn’t distinguish between active B12 levels and inactive analogues. If you want to ensure optimal B12 levels for females and males alike, opt for an active-B12 test.
  • If an active-B12 test isn’t available (this is very likely to be the case), aim for total-B12 levels of 500-550 or higher. This is because at these levels it’s rare to have low active-B12 levels, while below it (especially 350 and under) it’s a real risk.
  • Pay attention to clinical signs of B12 deficiency and supplement if necessary.
  • Be aware that B12 levels often drop during pregnancy, sometimes by as much as 50%. Don’t panic! This is normal, and is primarily a decrease in inactive-B12 levels. However, supplement with a good form of B12 daily, just in case.

Good luck 🙂

Optimal B12 Levels For Females: Full Explanation (2024)
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