Q & A Thursday: the B12 in your diet
Posted by kathryn in Nutrition
Continuing from Naomi’s question about iron and B12.
B12 is a whole different kettle of fish. It’s a curious, complex vitamin. Instead of being one molecule, B12 is actually a group of compounds, which are structurally similar and all contain cobalt.
What is vitamin B12?
- B12 can’t be made by either plants or animals. Instead it’s manufactured by bacteria and it ends up in our food as a result of this bacterial activity.
- The bacteria in your digestive tract can also make B12, which we can then absorb.
- It’s only required in tiny amounts, but B12 is hard to absorb and deficiency is common.
- To absorb this vitamin your digestion needs to be in relatively good shape. It takes actions and enzymes produced by your stomach, pancreas and small intestines to absorb B12.
Is it stored in the body?
- There are about 2,000 – 5,000mcg of B12 stored in the body. Mostly in the liver.
- B12 can be stored for years. The average intake needs to be about 2.4mcg per day to maintain these stores. But losses and gains occur over time, so this is an average figure.
- Deficiency symptoms can take five years or more to develop.
Sources of B12
- Our main source of B12 is animal foods and products, including milk and dairy.
- Plants only provide B12 when the soil they were grown in has not been washed away. For a long time mushrooms were advertised as being high in B12 and “meat for vegetarians”. But this is a myth. It is the soil surrounding the mushrooms that contains B12, not the mushroom itself.
- Some foods like tempeh and other cultured foods may contain small amounts of B12 – but these are not reliable sources.
How much do you need?
Current Australian RDIs specify 2.4mcg per day, although more is required in pregnancy and lactation.
- 1 cup of low fat yoghurt contains 1.4mcg
- 50g tinned salmon contains 0.75mcg
- 100g lean beef contains 1.9mcg
- 100ml fortified soy milk contains 0.3mcg
These a full list of the B12 in different foods at Food Standards Australia New Zealand.
What is Q & A Thursday?
This post is part of Q & A Thursday – a monthly burst of blogging, where you get to dictate the subject matter. Q & A Thursday is all about simple, practical answers to food and diet dilemmas sent in by readers.
If you have a question you’d like answered send me an "email":mailto:me@kathrynelliott.com.au. For more information you can take a look at the Q & A Thursday archives.
08 May, 2008
Comments
Hi Kathryn, loving the Q&A this month. I was wondering, what are the signs of B12 deficiency?
That’s a tricky one Vegeyum, as it’s often asymptomatic. The most frequent presentation is anaemia, as B12 is needed for the correct formation of red blood cells. As with iron-deficiency anaemia it presents with tiredness, etc and can be diagnosed with a blood test.
In more serious and long-term cases B12 deficiency causes nervous system damage. This can include numbness or tingling in hands and feet, problems with coordination and walking. But this appears after years of B12 deficiency and is very rare.
I’ve seen reports of 40 percent mild deficiency rates in Western populations. Prevalence is higher in vegans and the elderly, as the latter have problems absorbing B12.
If anyone is concerned, then it’s worthwhile visiting your GP and having the blood test.
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