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The dangers of vitamin B12 deficiencies

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A vitamin B12 deficiency can cause irreversible damage to the nervous system, but the condition is easily avoided.

QUESTION: I can’t absorb vitamin B12 from food and have to get it through regular injections. What is its role in the body?

ANSWER: Vitamin B12, or cobalamin, is essential for the proper functioning and development of the brain and nerve cells. A deficiency in the vitamin is dangerous because it causes progressive and irreversible damage. What starts as a bit of numbness and tingling in the hands and feet can cause permanent injury to the spinal cord and nerves outside the brain. Other effects include anaemia, fatigue, poor memory and stomach problems such as constipation, which result in weight and appetite loss. Prompt treatment is needed, because the longer the delay, the lower the chance of reversing the neurological complications.

The vitamin plays an important role in the synthesis of fatty acids contained in the myelin sheath that surrounds and protects nerves. It contains a cobalt atom, which, once cleaved from the vitamin, acts like a key, unlocking the enzymes that synthesise the acids for the sheath and also, importantly, enzymes involved in DNA synthesis.

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For that to happen we need plenty of B12-rich foods as well as the ability to extract the vitamin and absorb it.

A deficiency is not common in young adults, but it is in older people. A 2005 study, published in the European Journal of Clinical Nutrition, found 12% of older people in New Zealand were affected by the condition.

However, a 2018 study, published in the journal Nutrients, found that B12 needs were met by diet alone in more than 74% of older people. Their greatest food source contributors are milk, followed by beef, veal, fish and other seafood.

The vitamin is found only in foods of animal origin; there are no naturally occurring plant-derived forms. Vegans and some vegetarians will therefore need to eat B12-fortified foods or take supplements.

A B12 deficiency in older adults is usually caused by malabsorption, according to a 2010 study in Nutrients. This is because of reduced acid secretions in the stomach, which result in a decreased ability to extract B12 in food proteins.

Higher rates of atrophic gastritis among older adults are often blamed for the deficiency. The condition reduces secretions of gastric acids and intrinsic factor – a compound required for absorption of B12 from the gut.

However, the 2005 study found that although atrophic gastritis was a risk factor, it didn’t explain the majority of B12 deficiencies in older New Zealanders.

Malabsorption can also be caused by conditions such coeliac and Crohn’s disease, bowel resection, interference by bacterial overgrowth, chronic alcoholism and some less common genetic defects.

Certain medication-nutrient interactions may cause malabsorption, too, in particular, ulcer and reflux medication such as Losec, Pepcidine and Zantac, which reduce gastric acid secretions.

Pernicious anaemia, a condition affecting 1-2% of older adults, is characterised by a lack of intrinsic factor, which impairs B12 absorption from the gut, causing a deficiency.

A doctor must identify the problem. If malabsorption is the cause, eating more B12-rich foods won’t necessarily help and supplements might be required. Oral supplements don’t need to be cleaved from their protein source and are thus more available for absorption, and injections bypass the gut malabsorption problem altogether.

So, keep up your supplement regime as it’s an effective way to maintain vitamin B12 levels and prevent irreversible damage to your nervous system.

This article was first published in the June 22, 2019 issue of the New Zealand Listener.

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