Complications

Complication
Timeframe
Likelihood
long term
high

Those inadequately treated for vitamin B12 deficiency can have progressive neurological damage.

long term
high

Those inadequately treated for vitamin B12 deficiency can have progressive anaemia, leukopenia, and thrombocytopenia.

long term
low

Gastric cancer is a long-term complication of untreated pernicious anaemia (with antibodies to intrinsic factor). A two to threefold excess risk of gastric cancer has been noted in patients with pernicious anaemia.[81]

Stomach cancer

variable
high

Vitamin B12 deficiency may manifest with psychiatric symptoms such as cognitive impairment and irritability, or with conditions including dementia and depression.[43][59]

In one prospective study of adults aged ≥50 years, those with deficient to low vitamin B12 status were 51% more likely to develop depressive symptoms over 4 years.[110]

The potential for improvement of depressive symptoms in patients receiving vitamin B12 supplementation may differ between those with recent onset and those with more advanced neurological disorders.[106][107]

There is no clear evidence that vitamin B12 supplementation alone improves dementia or cognitive decline, although some studies suggest that supplementation with a vitamin B complex or folic acid combined with vitamin B12 may slow progression and improve symptoms.​​[7]​​[8][9][109]

Overview of depression

variable
low

One systematic review found that vitamin B12 deficiency is common during pregnancy and that levels of vitamin B12 decrease from the first to the third trimester.[30]

Vitamin B12 deficiency in pregnancy may be associated with an increased risk for preterm delivery, lower birth weight, and lower infant levels of vitamin B12.[56][57]

NHS Specialist Pharmacy Service: vitamin B12 deficiency: treatment during pregnancy Opens in new window​​

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