girl on a train with her head down to rest because of vitamin b12 deficiency

Vitamin B12 Deficiency

Vitamin B12 is an essential nutrient which humans cannot produce and must obtain from foods. However, it is almost exclusively found in animal food sources and may pose a problem for some vegetarians or vegans. Vitamin B12 is absorbed in a unique fashion, as we described in our previous article “Vitamin B12 in the Body”. According to the DGE, the recommended daily intake of vitamin B12 is 4.0 µg. There are several reasons why someone might not get enough vitamin B12 and this can lead to serious health consequences if the deficiency is not resolved. This article will describe both the causes and symptoms of vitamin B12 deficiency.

Check out our previous article on the importance of vitamin B12 and how our body absorbs this essential nutrient.

Risks for Vitamin B12 Deficiency

Low Intake

Vitamin B12 deficiency can be caused by reduced intake, reduced absorption or increased demand. Low intake leading to insufficient B12 levels is common for some diets, particularly for those who choose a vegetarian, vegan or plant-based diet. B12 is the only vitamin known to be absent in a diet based entirely on plant foods. Therefore, it is highly recommended that strict vegans regularly take B12 supplements or consume B12-fortified foods. Ovo-Lacto vegetarians who consume limited amounts of eggs and dairy may also benefit from taking supplements. Supplements and fortified foods are the only reliable substitutes to obtaining vitamin B12 from animal products.

Excess vitamin B12 is stored in the liver. The liver stores of vitamin B12 can provide the body with approximately a year’s supply of the vitamin once you choose to remove or limit animal products from your diet. However, this means long-term vegans are at a higher risk of suffering from vitamin B12 deficiency if they choose not to supplement.

Others may have fewer nutrients in their diets due to undernutrition. Undernutrition can lead to vitamin B12 deficiency, especially in at-risk populations such as the elderly. Those who suffer from anorexia or chronic alcoholism are also at risk of not getting enough B vitamins in their diet.

High Demand

Pregnant and breastfeeding women have a higher demand for B12 than other groups, requiring a daily intake of 4.5 and 5.5 µg to support the growth of their infant, respectively. Pregnant and breastfeeding mothers who also follow a vegan diet can risk symptoms of vitamin B12 deficiency in their infants if they do not meet the nutrient requirements. Mothers who do not consume enough B12-containing foods in their diet should choose supplements to avoid risks of B12 deficiency.

Poor Digestion

Some people eat enough vitamin B12-rich foods but are still prone to B12 deficiency because their digestive system cannot take up the vitamin. There are many causes for this problem which can be grouped into two categories. One is maldigestion, which is the reduced ability to breakdown foods, and the other is malabsorption, the reduced ability to absorb foods in the gut. Either type of digestive disorder can lead to B12 deficiency if not accounted for.

Vitamin B12 found in animal sources of food is bound to proteins. B12 must be freed from these proteins for it to be transported and absorbed successfully in the gut. Stomach acid helps break down these B12-protein bonds. Therefore, some conditions that affect stomach acid production can impair complete digestion of B12-rich foods. Pancreatic enzymes also help breakdown and transport vitamin B12 from food, and reduced pancreas function can also result in B12 deficiency. Fortunately, foods that are fortified with vitamin B12, or vitamin B12 from supplements, are not protein bound and can be absorbed despite maldigestion of B12 from most foods.

Poor Absorption

Following the digestion of vitamin B12 from food, the vitamin requires a protein called intrinsic factor (IF) to be absorbed through the intestines and into the bloodstream. IF is produced in the stomach and binds to vitamin B12 in the first segment of the small intestine and this IF-B12 complex is recognized and absorbed at a later part of the small intestine. The production of IF is needed to maintain adequate serum levels of vitamin B12 because very little B12 is absorbed without it.

Malabsorption of B12 occurs for some people who are unable to produce enough intrinsic factor, a condition known as pernicious anaemia. Inflammation in the small intestine can cause malabsorption of B12 by reducing the area for absorption; this is more common in people who suffer inflammatory conditions such as celiac disease or Crohn’s disease. Surgeries of the stomach or small intestines can also reduce the absorption of B12 by reducing IF production and absorption area, respectively.

The ability to absorb vitamin B12 is the most important risk factor because unlike maldigestion of vitamin B12-foods, a supplement cannot help those who suffer from malabsorption disorders. Instead, an intramuscular injection of vitamin B12 performed at a medical centre can provide vitamin B12 to the bloodstream.


Low levels of vitamin B12 in the blood can lead to a variety of symptoms depending on the severity of deficiency. Many of the symptoms of vitamin B12 deficiency can take a long time to manifest. It is important to intervene early and correct the cause of B12 deficiency to avoid permanent damage.

If left untreated, vitamin B12 can cause a condition called megaloblastic anaemia. Anaemia is a type of disease characterized by a decrease in the blood’s ability to carry oxygen. Megaloblastic anaemia is caused by a vitamin B12 deficiency and decreases the total number of healthy red blood cells.

Symptoms related to megaloblastic anaemia include:

  • Fatigue
  • Low appetite
  • Weakness
  • Headaches
  • Pale skin
  • Diarrhoea
  • Constipation

In addition to anaemia, vitamin B12 deficiency can cause neurological conditions. Signs of neurological damage are reported in approximately 20-30% of patients deficient for vitamin B12, and symptoms can occur independently of anaemia.

Symptoms associated with neurological damage include:

  • Reduced cognitive performance
  • Apathy
  • Depression
  • Listlessness
  • Psychosis
  • Poor memory
  • Dementia
  • Numbness and tingling in the hands and feet

Children who suffer from vitamin B12 deficiency risk impaired growth and cognitive development. Low vitamin B12 levels are also associated with cognitive decline in the elderly. However, many of the symptoms for megaloblastic anaemia and neurological damage are non-specific and may be caused by conditions unrelated to B12 deficiency.


Several groups have a higher risk of vitamin B12 deficiency:

  • Vegans and vegetarians
  • Elderly
  • Suffers from gastrointestinal disease
  • Pregnant or newborns

You should not wait for symptoms to appear before making changes to your diet. Check out the next article in our vitamin B12 series to see what the best B12-rich foods and our detailed supplement guide.

Part 3: Vitamin B12-Rich Foods

If you are unsure of your nutritional status, a blood test for vitamin B12 is a good way to determine if you are at risk of deficiency. Routine monitoring of vitamin B12 is especially important for those who suffer from celiac disease and Crohn’s disease.

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