Vitamin B12 and Perimenopause: What You Need to Know
Low B12 can make perimenopause fatigue and brain fog much worse. Learn the signs of deficiency and how to get enough through food and supplements.
Why Vitamin B12 Matters During Perimenopause
Vitamin B12 plays a central role in producing red blood cells, supporting the nervous system, and helping your body convert food into energy. When levels fall, the effects can look remarkably similar to perimenopausal symptoms: fatigue, brain fog, low mood, and tingling in the hands or feet. Because these symptoms overlap so heavily with hormonal changes, B12 deficiency is frequently missed in midlife women. Getting tested is straightforward, and identifying a deficiency can make a meaningful difference to how you feel day to day.
Who Is Most at Risk
B12 is found almost exclusively in animal products, so vegetarians and vegans are at significantly higher risk of deficiency. However, diet is not the only factor. Absorption depends on a protein called intrinsic factor, produced in the stomach lining, and this can become less efficient with age. Women who take metformin for insulin resistance, or who use proton pump inhibitors for reflux, are also at increased risk because both medications interfere with B12 absorption. If you have had gut surgery or have a condition such as coeliac disease or Crohn's, your ability to absorb B12 from food may also be reduced.
Signs Your B12 May Be Low
Persistent fatigue is the most common sign, particularly the kind that does not lift after a good night's sleep. Brain fog, difficulty concentrating, and memory lapses are also strongly associated with low B12, which can make them easy to attribute to perimenopause rather than a nutritional gap. Some women notice a low mood or increased anxiety. Physical signs include a sore or swollen tongue, mouth ulcers, pale or slightly yellowed skin, and in more advanced cases, numbness or tingling in the hands and feet. If any of these resonate, a blood test is a sensible next step.
How to Get B12 Through Food
The richest dietary sources of B12 are animal foods. Clams, liver, and other organ meats contain very high amounts. Fish such as salmon, trout, tuna, and sardines are excellent everyday sources. Eggs and dairy products, including milk, yogurt, and cheese, contribute meaningful amounts, though less than meat and fish. For vegetarians and vegans, fortified foods are the most reliable option: plant milks, breakfast cereals, nutritional yeast, and some soy products are commonly fortified with B12. Checking labels for the B12 content per serving is worth doing, as fortification levels vary significantly between products.
Choosing the Right B12 Supplement
B12 supplements come in several forms, including cyanocobalamin and methylcobalamin. Both are effective for most people. Methylcobalamin is often recommended for those with absorption issues or certain genetic variants, as it does not need to be converted before the body can use it. Sublingual tablets, which dissolve under the tongue, allow some absorption directly through the mouth lining and can be useful when gut absorption is impaired. For confirmed deficiency, particularly when caused by intrinsic factor problems, injectable B12 administered by a GP is the most reliable solution. Standard oral supplements are usually sufficient for dietary shortfalls.
B12 and Brain Health in Midlife
There is growing evidence that adequate B12 levels support cognitive function and may reduce the rate of brain shrinkage associated with ageing. In midlife, when many women already experience memory lapses and concentration difficulties linked to fluctuating oestrogen, keeping B12 in the optimal range is a reasonable priority. B12 works alongside folate and B6 to manage homocysteine, an amino acid that at elevated levels is associated with cognitive decline and cardiovascular risk. Eating a varied diet that covers all three B vitamins, or taking a B-complex supplement, addresses this trio together.
Getting Tested and Next Steps
A serum B12 blood test is available through your GP and gives a clear picture of your current level. Standard reference ranges vary between labs, but levels below 200 pg/mL are generally considered deficient, while levels between 200 and 300 are often described as borderline. If you are symptomatic in that borderline range, many doctors will treat anyway, especially given the safety of B12 supplementation. If heavy fatigue or brain fog are affecting your daily life, tracking these symptoms over time in the PeriPlan app can help you notice patterns and give your doctor a more complete picture of what is going on.
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