How much vitamin B12 do midlife women need?

I never thought much about vitamin B12 until brain fog hit me. Then I got my levels checked for the very first time at the doctor's over a year ago, and everything changed.

Vitamin B12 is a very important micronutrient at midlife. It not only helps make red blood cells, but it also plays a key role in the nervous system. Having optimal levels in blood and tissues helps to prevent disorders of the central nervous system, mood disorders, and vascular and Alzheimer’s dementia later in life.

Let’s think about that. Having suboptimal vitamin B12 levels over many years can negatively affect our cognitive health at older ages. We need more research because very few studies examine B12 needs at midlife according to a Cochrane review.

The reason B12 can go under the radar is that we can get enough from diet but still be deficient because of its complicated absorption. First, we need strong stomach acid to cleave B12 from food, a process that becomes less efficient with age. As people age, they are also more likely be taking medications like metformin and proton pump inhibitors, which interfere with vitamin B12 absorption.

A much smaller percentage of people deficient in B12 have pernicious anemia which occurs more frequently in those over 60 accounting for 1-2% of all deficiencies. In these cases, there’s an autoimmune reaction destroying intrinsic factor (another step in its absorption) so B12 cannot be absorbed. People with pernicious anemia need B12 injections.

Midlife is the ideal time to start thinking about vitamin B12 as should vegetarians (B12 is only found in animal foods), those with GI issues, and people on certain medications. The Institute of Medicine recommends all people over 50 consume supplemental sources of vitamin B12 either through fortification or supplementation. That's because the supplemental form of B12 does not need stomach acid to be utilized.

Although it's helpful, serum vitamin B12 is an imperfect marker. It can’t tell us for sure if our tissues have what they need. As I write about in the Midlife Woman's Biomarker Guide, when levels are normal with symptoms (<500pg/ml) or borderline (<300pg/ml), ask for a methylmalonic acid (MMA) and homocysteine test. When these two biomarkers are high, a vitamin B12 deficiency is likely.

If your levels are over 500pg/ml a vitamin B12 deficiency is not likely. But anyone with strange neurological symptoms should always get all the tests just to be sure it's not vitamin B12.

How much should we take to keep biomarkers optimal? The RDA is 2.4mcg but this may not be enough to keep tissue levels adequate. According to a study with healthy 18–50-year old’s, 4-7mcg was enough to keep MMY and homocysteine optimal. The researchers conclude:

Our findings, together with those of previous studies (7, 8, 19, 20), suggest that the current RDA of 2.4 lg vitamin B-12/d may be inadequate for optimal biomarker status

In his review in Blood, Ralph Green hematologist, Department of Pathology and Laboratory Medicine, University of California, Davis, recommends at east 10mcg/day of daily vitamin B12 to prevent problems.

A good multivitamin with higher B12 levels such as those found in over 50 formulations can work well. Although many B-vitamin complexes have mega-doses of B12 and it’s not toxic, some research suggests taking too much B12 may not be good either.

For example, one study showed women taking more than 20mcg of vitamin B12 and 35mg B6 had higher risk of fracture. Of course, this is one study, and more research is needed, but I can’t find evidence to justify such high levels for long period of times.

We just don’t have enough evidence to know for sure.

If you’re found to be deficient, you will be prescribed much higher levels often through B12 shots. What you take to prevent vitamin B12 deficiency is different than treating it.

But for now, getting a baseline vitamin B12 and tracking your levels while making sure you get the amounts your body needs can go a long way. 

Do you check your vitamin B12 regularly? Leave a comment and let me know!