Your Concern About Folic Acid and B12 Deficiency
The warning you read is accurate and important, but in your specific situation—where you received a B12 injection before starting folic acid and continue to receive B12 treatment—you are not at risk for precipitating subacute combined degeneration of the spinal cord. The critical danger occurs only when folic acid is given instead of or before B12 treatment in someone with undiagnosed or untreated B12 deficiency 1, 2, 3.
Why This Warning Exists
The concern about folic acid masking B12 deficiency is well-established and appears in multiple authoritative sources:
Folic acid can correct the anemia caused by B12 deficiency while allowing irreversible neurological damage to progress unchecked 1, 2, 3. This creates a dangerous situation where blood tests look better but the nervous system continues to deteriorate.
Subacute combined degeneration of the spinal cord is the specific neurological complication that can become permanent if B12 deficiency goes untreated 1, 3, 4. This condition involves demyelination of the dorsal and lateral columns of the spinal cord, causing symptoms like numbness, weakness, gait problems, and cognitive difficulties 5, 6, 4.
The FDA drug label for cyanocobalamin explicitly warns that "doses of folic acid greater than 0.1 mg per day may result in hematologic remission in patients with vitamin B12 deficiency" but "neurologic manifestations will not be prevented with folic acid, and if not treated with vitamin B12, irreversible damage will result" 3.
Why You Are Protected
Your situation differs fundamentally from the dangerous scenario:
You received a B12 injection before starting folic acid, and you continue taking B12 regularly 1. This means your B12 deficiency is being actively treated, so there is no risk of masked progression.
The danger only exists when folic acid is given to someone with untreated B12 deficiency 1, 2, 3. Once B12 treatment has begun, adding folic acid (if folate deficiency also exists) is appropriate and safe 2.
Current guidelines explicitly state that folic acid should be added only "after B12 treatment is established" 2. Your treatment sequence followed this correct protocol.
The Correct Treatment Sequence
The proper algorithm, which your hospital followed, is:
Diagnose B12 deficiency first (serum B12 <180 pg/mL or functional markers like methylmalonic acid >271 nmol/L) 1, 2.
Initiate B12 treatment immediately with intramuscular injections (typically hydroxocobalamin 1 mg on alternate days until improvement, then maintenance every 2-3 months for life) 1, 2.
Check folate levels simultaneously to identify any coexisting folate deficiency 2.
Only after B12 treatment has begun, if folate deficiency is documented, add oral folic acid (typically 5 mg daily for at least 4 months) 2.
Common Pitfalls to Avoid (That Don't Apply to You)
The warning you read is meant to prevent these errors:
Never giving folic acid "just in case" to someone with suspected B12 deficiency before confirming and treating the B12 deficiency 2. This is the dangerous scenario.
Never relying on improvement in anemia alone as evidence that B12 deficiency is resolved, because folic acid can improve blood counts while neurological damage continues 3, 4.
Never assuming that because someone feels better on folic acid, they don't need B12 evaluation 3, 4.
Your Ongoing Treatment
Since you are receiving both B12 injections and folic acid supplementation:
Continue your B12 injections as prescribed (typically monthly for life if you have malabsorption) 1. Never stop these even if you feel well, as the underlying cause of your deficiency likely persists.
Your 1 mg daily folic acid dose is safe and appropriate now that B12 treatment is established 7, 2. The 1 mg threshold mentioned in guidelines refers to the maximum safe dose for the general population to avoid masking undiagnosed B12 deficiency 7—a concern that doesn't apply once treatment has begun.
Monitor both vitamins at 3,6, and 12 months in the first year, then annually 1. Your healthcare provider should check serum B12, complete blood count, and potentially methylmalonic acid or homocysteine to confirm treatment adequacy 1.
Bottom Line
The article's warning is medically sound and important for preventing a serious complication, but it does not apply to your situation because you received B12 treatment first. The hospital followed the correct protocol by giving you the B12 injection before the folic acid tablet. You are protected from the risk of precipitating subacute combined degeneration because your B12 deficiency is being actively treated 1, 2, 3.