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Thursday 6 February 2020

Vitamins and Supplements (Things We Don’t Know about Pregnancy Series #13)

Is it a safe and good idea to take vitamins whilst pregnant? One thing’s for certain – it’s the norm.

Bacteria. Public Domain.
Whilst scientists have shown that taking certain specific vitamin supplements can protect you against diseases to which you are at risk, taking high, regular doses of multivitamins is actually proven to increase your risk of heart disease or cancer[1]. We don’t know why – it could be because of the fibre, or the various digestive pathways food goes through in your body – but swallowing a broccoli vitamins tablet just doesn’t do the same as eating a broccoli. It may also mean you are missing out on foods rich in other stuff your body needs, perhaps things we haven’t even discovered yet. Then there’s your microbiome: we still understand relatively little about this, but we know you can alter the microbial constitution of your gut through diet and use of supplements.

Overall, a varied diet is recommended as the most healthy one – supplementing where necessary.

If you’re having a baby, you may have increased needs for certain nutrients. Supplementing is generally advised for all pregnant women – but should it be? Do we actually absorb many of the nutrients in tablets, and do they make any difference?

In particular, I wanted to know this – because I’m a vegetarian.

Women who especially may need to consider supplementing include those who have “gone off” fruits and vegetables, those with particular conditions, poor absorption capacities, or those expecting a baby born in winter. What we don’t know is whether vegetarians and vegans should supplement more than meat-eaters. A body of contradictory evidence shows that we don’t know whether vegetarians and vegans are healthier or less healthy than meat-eaters[2]. This is largely due to environmental effects: in Western culture, people who choose plant-based diets tend to be more health conscious than the average person, smoking and drinking less and exercising more. Elsewhere, many vegetarian and vegan cultures have survived healthily for thousands of years[3].


Everybody needs iron: it sits at the centre of the haemoglobin molecule, binding to oxygen and carrying it through to blood to where it is needed in cells throughout the body. During pregnancy, the mother’s blood supply increases by a further 20-50%[4], and the baby is also busy making blood, so iron demand increases. Pregnancy-based anaemia is not uncommon, and it’s important to get in lots of iron rich foods and vitamin C, which supports the absorption of iron. Most supplementary vitamins contain iron.

If you’re a vegetarian or vegan, vitamin C is especially important because the iron found in vegetables (dried fruits, seeds, nuts, pulses, tofu, cocoa, beans, wheat, green leafy vegetables and, apparently, black treacle!)[3] is less bioavailable (absorbable) than the iron found in meat, although it can be more abundant.

Vitamin C is abundant in citrus fruits and green vegetables including spinach, cabbage, broccoli and green peppers.

Cabbage by fir0002flagstaffotos via Wikipedia Commons.

Vitamin B12

Most B vitamins are widely available in grains, but vitamin B12 (cobalamin) is a special case. This vital nutrient supports the functioning of the nervous system and blood formation, so is particularly important for pregnant women. However, it’s only found in trace amounts outside meat and dairy products, except in fortified foods like cereals, soya milks and yeast extract. Researchers are unsure whether vegan sources of B12 are adequate. This is because measuring the quantity of B12 in foods is very difficult: there are several molecules similar to B12 (known as “analogues”) that disrupt the body’s use of B12. This means that a food measured to contain B12 may actually not contain B12 at all, just its analogues. It’s also possible that both are present, in which case if the analogues are in similar quantities to the B12, the B12 may not be accessible. Food can only be declared a reliable source of B12 if there is evidence that it corrects or prevents deficiency.

Scientists are also unable to tell how long B12 stores in the body will last – they can diagnose deficiency, but not predict it.

If you get it naturally on a vegan diet, you may get it mostly from soil – yes, that’s right, from dirty vegetables. Whilst the liver can store B12 for up to 3 years, you can’t guarantee dirty vegetables will supply enough, and in any case should be avoided unwashed foods because of toxoplasmosis.

Toxoplasmosis is a parasitic disease common in cats that can be caught from meat (and, occasionally, soil!). © TWDK

If you’re vegan, and if you’re pregnant, supplement for vitamin B12.

Vitamin D

Vitamin D helps the body absorb calcium, and is thus important when you’re building baby bones. It’s found in fish, eggs, dairy, fortified breakfast cereals, beans, and green leafy vegetables, and is made by the body when exposed to sunlight*. This means that no matter whether you’re a vegetarian or a meat-eater, you can be deficient in vitamin D during the winter when it’s dark most of the time we’re outside. As such, supplementing for vitamin D is a good idea. My midwife suggested that after the first trimester I switched from a multivitamin to just a little vitamin D capsule, as my baby is due in February.

*Vitamin D is not a good excuse to overexpose yourself to sunlight.

Omega acids

Fish are a good source of omega 3 fatty acids, vital nutrients essential for brain development, blood and heart regulation. Scientists are still investigating other health benefits, but it’s been suggested that they are preventative towards cancer, dementia, and rheumatoid arthritis. There are three types of omega 3 fatty acids in foods: ALA (alpha-linolenic acid), which is also found in plants, and EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid), which are much less available in sources other than fish. The body can convert ALA into these other types, but it’s not very efficient. It’s not clear whether vegetarians and vegans need to supplement for EPA and DHA, though some recommend it.

Fish, however, especially large fish such as tuna, can be a source of heavy metals such as mercury, which can damage the brain and nervous system. So how much fish should we eat? Does the risk of environmental contaminants outweigh the risk of being deficient in essential fatty acids at a time when you need them more than ever? A pregnant woman is, after all, growing at least one whole new brain from scratch, and she needs essential fatty acids to do that. This dilemma really needs addressing, because at the moment mothers are being pulled in two different directions.

Pills. Image credit: frolicsomepl .

Vitamin A

Vitamin A is essential for growth and development, and healthy eyesight and immune system. As such, you’d think it was important for pregnant women to get lots of it, but in fact pregnancy vitamins are low on vitamin A and healthcare professionals warn against taking too much. This is because the liver stores it, and can accumulate dangerous levels, whereupon it starts to act as a toxin and cause birth defects in babies. Liver is also not recommended in the diet of pregnant women for the same reason. Normally, vitamin A levels in the livers of herbivores are safe, but during pregnancy you should watch out (carnivores, on the other hand, accumulate dangerous vitamin A levels, especially as they age, which is how Antarctic explorers poisoned themselves by eating dog liver during desperate time).

Folic acid

Folic acid helps us build proteins for growth, including the metalloprotein haemoglobin, and metabolise DNA. For pregnancy, we need 10 to 20 times as much as normal[5] to build neural networks, but this needs to be in your system before you conceive. This means that folic acid is an essential nutrient to get before having a baby and during the first trimester, coming mainly from green leafy vegetables, pulses and avocados, but also fortified in breakfast cereals and in pregnancy-specific vitamins.

However, importantly, recent research has suggested that getting too much folic acid later in pregnancy can mask vitamin B12 deficiency[6] and may increase the risk of autism[7]. Current research is inconclusive and so ongoing. Luckily, it seems unlikely that it would be possible to get too much folic acid from foods naturally rich in it, and it takes supplementation or foods that are enriched to get too much, so stopping taking it after 12 weeks is probably the safest course of action.

There are many unknowns when it comes to pregnancy, and over the next few months, I’ll be exploring more of them with you. Look out for my next blog post, which will be about baby brain.

To read our full article on the things we don't know about pregnancy, check out our site. This article will be updated as we add posts across the coming months.

why don't all references have links?

[1] Martínez, María Elena, et al. Dietary supplements and cancer prevention: balancing potential benefits against proven harms. Journal of the National Cancer Institute 104.10 (2012): 732-739.
[2] Ginter, E. Vegetarian diets, chronic diseases and longevity. Bratisl Lek Listy 109.10 (2008): 463-466.
[3] Vegetarian and Vegan Mother and Baby Guide, Rose Elliot, Viva! and the Vegetarian and Vegan Foundation, 2001. Brighton.
[4] Hytten, Frank. Blood volume changes in normal pregnancy. Clinics in haematology 14.3 (1985): 601-612.
[5] Soma-Pillay, Priya, et al. Physiological changes in pregnancy. Cardiovascular journal of Africa 27.2 (2016): 89.
[6] Morris, M.S., Jacques, P.F., Rosenberg, I.H., et al. (2007). Folate and vitamin B12 status in relation to anemia, macrocytosis and cognitive impairment in older Americans in the age of folic acid fortification. Am J Clin Nutr; 85(1):193–200.
[7] Beard, C. Mary, Laurel A. Panser, and Slavica K. Katusic. Is excess folic acid supplementation a risk factor for autism?. Medical hypotheses 77.1 (2011): 15-17.

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