High MCV with low B12

by Greg

I recently had a blood workup, and my MCV and MPV levels were both high. 94 on the MCV. I'm 60 years old, and looking back over the years since 1995, my MCV typically runs from 90 to 101. However, recently the upper limit has dropped to 92, therefore, the 94 stood as an outlier.

My physician was astute enough to see this and said "let's do another blood test to check for B12 deficiency". Test came back with B12 levels 382; low end of normal.

I did a bit of internet research, and sure enough, I have a few (1 mo to 1 yr) of the typical symptoms of B12 deficiency.

I'm athletic, getting plenty of aerobic exercise (but not overdoing it). No prescription or other drugs, don't smoke, very minimal alcohol usage. We eat pretty healthy, not much red meat. No concerns about heart disease, etc.

I take a few vitamins daily (multi, calcium, etc), and a baby aspirin dr recommended.

So, my questions:
1) Is it likely that I have been B12 deficient for decades?
2) If the recommended daily amount of B12 is 6 mcg/day, why am I prescribed 1000 mcg/day for six months to bring B12 values into the nominal 600's range?
3) I've read that aspirin can interfere with B12 absorption. I'm considering dropping the daily baby aspirin. Yes?
4) If my B12 levels come into normal ranges, would my past and future normal eating B12 intake at, say, 12 mcg/day suffice?
5) How long does it take for the typical person to drop from a nominal B12 level with these large supplements to their deficient level without taking the supplements?

Thank you!

Comments for High MCV with low B12

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Lots of Questions
by: Kerri Knox, RN

Awesome to see a doctor actually know what a high MCV means and that an MCV Blood Test can be used to find Vitamin B12 Deficiency.

Fortunately, you actually had low B12, but most people's B12 levels are within the 'normal' limits on a vitamin b12 test- even though they are still deficient since the 'normal' vitamin B12 levels used in the US are generally incorrect and don't catch actual vitamin B12 deficiency even when the test is done. But in your case, you were 'lucky' to have low enough vitamin B12 levels that you actually got a diagnosis.

1) I don't know. However, it takes about 3 to 4 years of Vitamin B12 deficiency to show up on lab results as a high MCV. So, it's possible that you've been at least marginally vitamin B12 deficient for a long time. Prior to 1995, most likely.

2) Because that is the dose it takes to 'fill up' your liver again and bring your levels higher. Why he's prescribing it for 6 months is strange though.

3) Aspirin can cause leaky gut and stomach irritation, which can then interfere with vitamin b12 absorption. I cannot in any way advise you whether or not to keep taking the aspirin. There are pros and cons you need to discuss with your health care practitioner.

4) How will you be sure you are getting 12 mcg of Vitamin B12? And why do you think that if you couldn't absorb vitamin B12 for decades, that taking vitamin B12 will suddenly change that? There is a reason that you were unable to absorb B12, taking B12 for 6 months will not change your ability to absorb B12 from food in the future. There is an underlying reason why you are not absorbing B12. See my page on Vitamin B12 Malbsorption.

5) I don't know. It depends upon how deficient you are and how much you are using. There is no 'formula'. There is also no 'downside' to taking B12 for life. I take large doses (10 to 20 milligrams, which is 10,000 to 20,000 micrograms) of Methylcobalamin B12 once a week or so, despite not having Vitamin B12 Deficiency, simply to prevent Vitamin B12 Deficiency in the future, and for the many benefits of Methylcobalamin.

While 1000 mcg is the 'standard' dose for Vitamin B12 Deficiency, it's not necessarily the proper dose for the proper functioning of the body. See the page on Vitamin B12 Deficiency Treatment to see why anyone with fatigue or other health issues might want to consider taking 'enough' methylcobalamin B12 for an 'optimal level of well being', which, in one study, took upwards of 10,000 mcg per day.

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Kerri Knox, RN- The Immune System Queen
Functional Medicine Practitioner
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