In this post I’m going to look at the B vitamins in nutrition and health. But let’s take a step back and actually look at what a vitamin is, and isn’t. In order to be defined as a vitamin, a molecule must meet four criteria.
- A vitamin must be an organic compound, very simply this means it must contain at least one carbon atom.
- Vitamins must be vital to life, i.e. without it a person could not survive.
- They are required in limited amounts, this definition is the most woolly as there is no hard description of what “limited” refers to.
- Finally, vitamins cannot be synthesized by a person in sufficient quantities, i.e. they must come from the diet.
Let’s look at a few common nutrients to see if they tick all the boxes.
What are vitamins?
We’ll start with iron. Whilst it ticks the latter three points, iron falls at the first hurdle as it doesn’t contain a carbon atom. A compound containing both iron and carbon (such as iron carbonate) passes this check, but then fails on the vital to life aspect, as whilst iron is vital to life, iron carbonate is not.
OK, let’s pick something a bit more complex. Glucose is a simple carbohydrate, is definitely vital to life, and since it contains six carbon atoms it passes that point as well. But it falls down on the other two points, firstly because it can be synthesised in the body from the longer complex carbohydrates and fats that we eat, and secondly because it is required in large amounts to provide energy.
Let’s try one more example, ascorbic acid or Vitamin C, a very famous vitamin indeed. Containing six carbon atoms it passes the first point, it is defiantly vital to life as it plays a key role in tissue maintenance and repair. Indeed, diseases such as scurvy, characterised by breakdown of the bodies tissues, rapidly appear in the absence of ascorbic acid.
The exact amount required isn’t known but estimates range from 60-100 mg per day, with little to know benefit from exceeding this amount, so we can definitely say it’s required in limited amounts. Finally, ascorbic acid cannot be synthesised directly by humans, rather we must obtain it from food (citrus fruits and tomatoes are especially rich) or via supplements. It ticks all the boxes and so is classed as a vitamin. Interestingly, most plants and animals on the planet can synthesise ascorbic acid, whereas humans and a few other species can’t. So, whilst ascorbic acid is a vitamin for us, it isn’t for most other species.
You may have noted that above I said ascorbic acid was the most common form of vitamin C. This is important as vitamins are classified based on function, not exact structure. So for example sodium ascorbate is also classified as vitamin C.
There are currently thirteen recognized vitamins. Vitamin A, C, D, E and K and 8 types of B vitamin. The functions of these vitamins is very diverse, for example vitamin C is important in tissue repair, whereas vitamin D, which I’ve talked about previously, is important for regulating bone mineral metabolism. In this post I’m going to focus on the eight B vitamins, their sources, and the proposed health benefits of each.
The B Vitamins
B vitamins are a class of water (as opposed to fat) soluble vitamins which play an important role in many cellular processes. When present in supplements individually, B vitamins are referred to by their individual name, for example, vitamin B1. When all are present they are often termed “vitamin B complex.”
Below is a quick summary table of the B vitamins, but I’ll give more info about the role of each, the potential harmful effects arising from a lack of each, and where available, information about the recommended daily amount of each.
|Vitamin||Alternative Name||Brief Function|
|B1||Thiamine||Breakdown of sugars and amino acids|
|B2||Riboflavin||DNA repair, ATP (the energy currency of the body) generation|
|B5||Pantothenic acid||Breakdown of sugars and amino acids, synthesis of fatty acids and amino acids|
|B6||Pyridoxine||Synthesis of amino acids|
|B7||Biotin||Fatty acid synthesis, break down of sugars|
|B9||Folic acid||DNA synthesis and repair, important for rapid cell division|
|B12||Hydroxocobalamin||DNA synthesis and repair, fatty acid and amino acid synthesis|
Vitamin B1 – Thiamine
Thiamine’s major role is to act as a coenzyme (helps catalyse a reaction) involved in the breakdown of sugars and amino acids into their constituent parts. These are then available to be used to make other molecules required by the body.
As such, a severe deficiency in thiamine can prove fatal with symptoms including weight loss, loss of sensory perception, weakness, pain, increased heart rate, and shortness of breath. These symptoms are sometimes taken together and classed as Beriberi disease, although it is also commonly referred to as thiamine deficiency. Whilst very severe cases are rapidly identified, low level occurrences of these symptoms can pass un-noticed for many years or often be misdiagnosed .
However, a relatively simple blood test is possible.
Thiamine is readily available in many foods, including numerous food containing yeast based products or cereal grains, in particular those containing the wholegrain. Other rich food sources include asparagus, kale, liver and eggs. For adults the Recommended Dietary Allowances (RDA) are 1.2 mg in men and 1.0 mg in women, rising to 1.4 mg during pregnancy and breastfeeding.
Vitamin B2 – Riboflavin
Riboflavin acts as coenzyme and plays a major role in the production of ATP, the bodies “energy currency”. Deficiencies in riboflavin are uncommon in the West as many of our foods are enriched during their processing. However, when Riboflavin deficiency is present, symptoms can include inflammation of the skin, especially around the lips and the mouth, light sensitivity and anaemia. In very severe cases there is a severe lack of energy which eventually leads to the collapse of the bodies systems. However, this is incredibly rare and often associated with severe malnutrition .
Outside of the widely available fortified foods, liver, milk, mushrooms, spinach and almonds are all rich sources of riboflavin. The RDA for men over the age of 14 is 1.3 mg per day and 1.0 mg per day in women rising to 1.4 mg during pregnancy and 1.6 mg during breastfeeding.
Interestingly, when added to a B complex formula or a multivitamin, B2 seems to have a protective effect against an increased cancer risk associated with high doses of certain B vitamins.
Vitamin B3 – Niacin
Niacin is the most common form of vitamin B3, with nicotinamide being another common form. As with riboflavin, both niacin and nicotinamide play an important role in the generation of ATP, but are also important in the break down of dietary fats, carbohydrates and proteins and the synthesis of carbohydrates and fatty acids.
As with riboflavin, deficiency of niacin leads to the development of inflammatory disorders, but also similarly to riboflavin this is now incredibly rare in the West due to fortification of foods .
One interesting usage of niacin, but not nicotinamide, is as a lipid-lowering medication. Acting to reduce the amount of low-density lipoproteins and increase the amount of high-density lipoproteins. Although as we know from this previous post such an effect may not be entirely desirable .
Foods rich in niacin include liver, tuna, salmon, avocados, leafy vegetables, dates and wholegrain cereals. The RDA for men is 16 mg per day and 14 mg per day for women with an upper limit of 35 mg per day for each. At doses exceeding this there are some mild side-effects including facial flushing whereby blood rushes to the face causing a redness and tingling.
Vitamin B5 – Pantothenic acid
Pantothenic acid is a cofactor used in the synthesis of coenzyme A, which is important in the synthesis of fatty acids and the generation of ATP. As the “pan” in its name would suggest, pantothenic acid is found in nearly every food, in part because it is so vital to life.
Deficiency in pantothenic acid is virtually unheard of as it is so prevalent in the diet, although some small trials have described similar effects to those seen with other B vitamin deficiencies .
The RDA for pantothenic acid has been set at 5 mg per day for men and women, increasing to 7 mg per day for pregnant and breastfeeding women. No upper limit or side effects have been described.
Vitamin B6 – Pyridoxine
Pyridoxine is vital in the synthesis of amino acids and important neurotransmitters such as serotonin, dopamine and GABA. Deficiency of pyridoxine gives rise to similar symptoms described above including inflammation and a lack of energy or confusion. Although severe deficiency is uncommon low level deficiency can be relatively common and as with other B vitamin deficiencies can be missed or misdiagnosed.
Foods rich in pyridoxine include chick peas, bananas, pork and beef. The RDA for pyridoxine is 1.7 mg per day for men and women rising to 2.0 mg per day for pregnant and breast feeding women. As with all B vitamins pyridoxine is water soluble meaning that excessive doses are often passed out in urine. However, continued very high doses of pyridoxine are associated with very severe side effects including the development of heart arrhythmia and neurological damage. Confusingly, the maximum recommended dose varies quite widely, set at 10 mg per day in the UK, 25 mg per day by the EU and 100 mg per day in the US.
Vitamin B7 – Biotin
Biotin is required for the production of fatty acids, and the break down of sugars, potentially to maintain blood sugar level. Biotin is commonly recommended as a dietary supplement for the strengthening of nails and hair. These claims arise from the fact that these symptoms arise when biotin is deficient, as well as other more common B vitamin deficiencies including inflammation of the skin. However, data supporting a beneficial effect in those already obtaining the required amount of dietary biotin is weak [6,7].
Whilst severe deficiency is rare, mild deficiency may be relatively common due to dietary deficiencies. Rich dietary sources include leafy green vegetables, nuts and egg yolks (but not the whites which contain avidin which neutralises biotin). Importantly there is no current RDA for biotin, rather there are “Adequate Intakes” which are meant to act as a guide until better information is available. These are currently set at 30 μg per day for both men and women.
Vitamin B9 – Folic acid
Vitamin B9 is perhaps the most famous of all the B vitamins due to its importance role in pregnancy and early infancy. Folic acid is converted into tetrahydrofolic acid which acts as a cofactor in many cellular reactions, but especially the synthesis of amino acids and nucleic acids, vital for rapid cell division. Times when rapid cell division is important? During pregnancy and early infancy, and also in the production of red blood cells which have a rapid turnover within the body.
As you can imagine a deficiency of folic acid is associated with some poor health effects. In pregnancy a lack of folic acid was linked with the risk of neural tube and congenital heart defects which are a major causes of miscarriage and early infant death [8,9]. As such folic acid supplementation is strongly recommended before and during pregnancy and also in the babies diet after birth.
Outside of pregnancy folate deficiency can lead to a variety of symptoms including depression, confusion, anaemia and fatigue . Anaemia caused by a lack of red-blood cell production may be the major symptom here driving the development of the other symptoms such as depression and fatigue as the brain is not being supplied with sufficient energy.
Foods rich in folic acid include leafy green vegetables such as spinach or kale as well as citrus fruits and many cereals. Fortified bread The RDA for folic acid varies by age and sex. For those over 14 years old a dose of 400 μg (micro-gram) per day is recommended, increasing to 600 in pregnant women and 500 in breastfeeding women. An upper limit of 1,000 μg per day has been recommended although no harmful effects have been associated with high levels of consumption. Interestingly there is some suggestion that high intakes of folic acid can mask vitamin B12 deficiency which can be much more serious, although no in-depth study has yet been performed .
Vitamin B12 – Hydroxocobalamin
Finally, to hydroxocobalamin. The most important role of hydroxocobalamin is in the synthesis of DNA in a similar fashion to folic acid, hence why it is possible for an excess of folic acid to mask a deficiency of hydroxocobalamin. Whilst there is a large overlap in function between the two hydroxocobalamin seems to also play an important role in the maintenance of adult neurological tissue in the brain. As such a deficiency can lead to several severe neurological disorders such as a loss of sensation, dementia and other neurological conditions, which unlike other vitamin B deficiencies may not be reversible [12,13].
Most animal derived foods including fish, meat, poultry and eggs is rich in hydroxocobalamin meaning vegetarians of vegans are strongly recommended to supplement their diet. A RDA of 2.4 μg per day for men and women has been set, rising to 2.8 μg per day in pregnant and breastfeeding women. No adverse effects have been associated with excess vitamin B12 intake from food or supplements in healthy individuals.
So hopefully that’s given you some understanding of the role of the various B vitamins, their sources and the potential effects arising from a deficiency. Eating, a healthy, varied diet rich in dark green vegetables, whole grains and meats should provide sufficient quantities of all B vitamins.
However, whilst it is often easy to identify severe cases of B vitamin deficiency, milder low-level deficiencies are often easily missed, or misdiagnosed. But with readily available tests to check the levels of your B vitamins and numerous supplements this should not be something impacting your health.
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