Diabetes and B12: Why This Vitamin Matters

Why does this matter?

Millions of people with diabetes in the United States may be experiencing avoidable nerve damage that is worsened by, or even caused by, vitamin B12 deficiency. This problem is often mistaken for diabetic neuropathy, even though it is relatively easy to prevent and treat.

Vitamin B12 supports nerve health by helping preserve the protective myelin sheath that prevents nerve injury. Too little B12 can contribute not only to diabetic nerve pain, but also to autonomic neuropathy associated with diabetes.

Some numbers

An estimated 2.2 million cases of neuropathy in the United States are linked directly to metformin use rather than diabetes alone. Many of these cases could be prevented or improved by giving people who take metformin a multivitamin with a high dose of vitamin B12.

Why? Metformin blocks B12 absorption. About 45% of patients taking metformin have diabetic or other peripheral neuropathy, compared with 32% of diabetics who are not taking metformin. Even so, metformin remains an excellent medication.

That is only the beginning. Overall, vitamin B12 deficiency is estimated to contribute to 10 million preventable cases of neuropathy in the United States, and it is still often mislabeled as diabetic neuropathy.

• Metformin is only one of many reasons diabetics are at high risk for B12 deficiency. The prevalence of vitamin B₁₂ deficiency in diabetic patients taking metformin has been reported to be as high as 93%.

What other factors can cause B12 deficiency in diabetics?

• About 15% to 40% of diabetic patients use proton pump inhibitors (PPIs) such as omeprazole because diabetes mellitus can lead to gastroesophageal reflux disease (GERD) and gastroparesis. PPIs markedly reduce B12 absorption, as does...
• Small intestinal bacterial overgrowth (SIBO), which occurs in 8% to 15% of the general diabetic population. That figure rises to ~45% in patients with diabetic gastroenteropathy, autonomic neuropathy, or chronic dyspepsia, and it increases further to 76% among those taking GLP1 medication.

Can a B12 level be checked?

Unfortunately, this easily preventable issue is not being properly addressed. Medical guidelines recommend frequent vitamin B12 testing in patients taking metformin, yet a recent review found that fewer than 20% of doctors are checking these levels. The result can be serious.

B12 deficiency can contribute to neuropathy even when the blood level appears normal. A typical vitamin B12 blood range is 200 to 900 picograms per milliliter (pg/mL). Research suggests that higher levels, around ∼400 pmol/L [or 542 pg/mL], may be needed for optimal neurological function. Relying on a normal result near 200 pg/mL may miss most people who could benefit from supplementation.

Another concern?

Even with an elevated B12 level, about 6% of the population has a genetic enzyme deficiency that prevents B12 from reaching the brain. In other words, neuropathy can still be linked to B12 problems even when blood levels are high. A simple, low-cost supplement at an appropriate dose may be the safest approach.

Is a standard multivitamin enough?

Unfortunately, because diabetes interferes with B12 absorption in so many ways, the RDA of 2.4 micrograms is not enough. The following recommendations are intended to be discussed with a personal healthcare professional:

1. All diabetics should take a multivitamin containing 500 mcg of B12 as methylcobalamin. This should be done regardless of blood level. Since recent research also suggests vitamin D may reduce diabetic neuropathy pain, the supplement should also include vitamin D 1000 IU.
2. If diabetic neuropathy is already present, add a daily 5,000 microgram (5 milligram) B12 tablet for one year. The methylcobalamin form is preferred. It does not matter much whether it is sublingual or swallowed as a tablet. If the neuropathy is severe, a holistic physician may also consider methylcobalamin B12 injections for at least three months.

This is a strong example of why prevention matters. After nearly half a century of treating chronic pain, it is clear that most pain can be managed effectively. The bigger issue is not a lack of treatments, but a lack of meaningful physician education.