I am lucky with this topic as I can get a substantial start by referring to the course materials from my Nutritional Therapist Diploma Course, from The Health Sciences Academy.  Unless I list other sources, this is the main source of my information.

As a first note, it is generally best to ensure you get all the B vitamins as they mostly work better together, and it might not do much good if you took one type and didn’t get enough of another which is essential to its function.  I am thus including in my lists of each, their promoters (what is needed to help make them effective) and their adversaries (what might interfere with them being able to work).  You might notice that many of them are found in the same sort of foods anyway.

The vitamin B complex consists of a range of Vitamin B’s:

Vitamin B1 or Thiamine

Effective for: Energy production, brain function, and digestion.  Helps the body make use of protein.

Top food sources: Watercress, squash, courgette, lamb, asparagus, mushrooms, peas, lettuce, peppers, cauliflower, cabbage, tomatoes, brussel sprouts, beans.

Deficiency symptoms: Tender muscles, eye pain, irritability, poor concentration, poor memory, stomach pains, constipation, prickly legs, tingling hands, rapid heartbeat.

Promoters: Works with other B vitamins, magnesium, manganese.

Adversaries: Antibiotics, tea, coffee, stress, birth-control pills, alcohol, alkaline agents (such as baking powder or bicarb), sulphur dioxide (preservatives), overcooking, processed foods.

RDA: 1.4 mg

B2 or Riboflavin

Effective for:  Helping to turn fats, sugars, and proteins into energy.  Repairing and maintaining healthy skin, inside and out.  Helping to regulate body acidity.  Important for hair, nails, and eyes.

Top food sources:  Mushrooms, watercress, cabbage, asparagus, broccoli, pumpkin, bean sprouts, mackerel, milk, bamboo shoots, tomatoes, wheat germ.

Deficiency symptoms:  Burning or gritty eyes, sensitivity to bright lights, sore tongue, cataracts, dull or oily hair, eczema or dermatitis, split nails, cracked lips.

Promoters:  Works with the other B vitamins and Selenium.  Best supplemented as part of a B complex, with food.

Adversaries:  Alcohol, birth control pill, tea, coffee, alkaline agents (such as baking powder or bicarb), sulphur dioxide (preservative), overcooking and food refining or processing.

RDA:  1.6 mg

B3 or Niacin (or Nicotinamide or Niacinamide)
Effective for:  Energy production, brain function, skin.  Helps balance blood sugar and lower cholesterol levels.  Also involved in inflammation and digestion.

Top food sources:  Mushrooms, tuna, chicken, salmon, asparagus, cabbage, lamb, mackerel, turkey, tomatoes, courgettes and squash, cauliflower, whole wheat.

Deficiency symptoms:  Lack of energy, diarrhoea, insomnia, headaches or migraines, poor memory, anxiety or tension, depression, irritability, bleeding or tender gums, acne, eczema, dermatitis.

Promoters: Works well with other B complex vitamins and chromium, best taken with food.

Adversaries:  Antibiotics, tea, coffee, birth control pill, alcohol.

RDA:  18 mg

B5 or Pantothenic Acid

Effective for:  Energy production, controlling fat metabolism, brain and nerves.  Helps make anti-stress hormones (steroids) and helps maintain healthy skin and hair.

Top food sources:  mushrooms, watercress, broccoli, alfalfa sprouts, peas, lentils, tomatoes, cabbage, celery, strawberries, eggs, squash, avocados, whole wheat.

Deficiency symptoms:  Muscle tremors or cramps, apathy, poor concentration, burning feet or tender heels, nausea or vomiting, lack of energy, exhaustion after light exercise, anxiety or tension, teeth-grinding.

Promoters:  Works with other B complex vitamins. Biotin and folic acid aid absorption. Best taken with food.

Adversaries:  Stress, alcohol, tea, coffee, and it’s destroyed by heat and food processing.

RDA: 6 mg

B6 or Pyridoxine such as in meat, whole grains, most vegetables, nuts, etc.

Effective for: Protein digestion & utilisation, brain function, hormone production.  Helps balance sex hormones, hence use in PMS and Menopause.  Natural anti-depressant & diuretic.  Helps control allergic reactions.

Top food sources:  Wheat germ, watercress, cauliflower, cabbage, red kidney beans, peppers, bananas, squash, broccoli, asparagus, brussel sprouts, lentils, eggs, onions, salmon, tuna, turkey.

Deficiency symptoms:  Infrequent dream recall, water retention, tingling hands, depression, anxiety, irritability, muscle tremors or cramps, lack of energy, flaky skin.

Promoters:  Works with other B-complex vitamins as well as with zinc and magnesium.

Adversaries:  Alcohol, smoking, birth control pill, high protein intake, processed & refined foods.

RDA:  2 mg.  This one can cause toxicity if you overdose on taking it without the other B vitamins in the B vitamin complex to balance the intake.

B12 (Cyanocobalamin is the most stable source) such as in meat, liver, shellfish, milk, etc.  Your body converts it to the two active forms of vitamin B12, which are methylcobalamin and adenosylcobalamin.

Effective for:  Making use of protein, helping blood carry oxygen (so essential for energy).  It’s needed for synthesis of DNA, essential for nerves, and it deals with tobacco smoke and other toxins.

Top food sources:  Oysters, sardines, tuna, lamb, eggs, shrimp, cottage cheese, milk, turkey and chicken, cheese.

I noticed that a vegan diet excludes all of these sources – so I looked up what sources might help for vegans.  The vegan society says “It’s essential that all vegan diets contain a reliable source of vitamin B12. This nutrient is needed to help speed up reactions in your body, and deficiency can cause anaemia and nervous system damage. Vitamin B12 is made by micro-organisms, and isn’t produced by plants. Fortified foods and supplements are the only proven reliable sources for vegans. Vitamin B12 is added to some alternatives to milk products, vegan spreads, nutritional yeast flakes, yeast extracts and breakfast cereals.”

Deficiency symptoms:  Poor hair condition, eczema or dermatitis, pale skin, mouth sensitivity to heat or cold, irritability, anxiety or tension, lack of energy, constipation, tender or sore muscles.

Promoters:  Works with folic acid.  Best taken as B complex, with food.

Adversaries:  Alcohol, smoking, lack of stomach acid.

RDA:  1.5 mcg

Folic Acid (Folate or B9) such as in leafy veg, sunflower seeds, yeast, liver, etc.

Effective for:  Critical during pregnancy for development of brain and nerves in the baby.  Always essential for brain and nerve function.  Needed for utilising protein and for red blood cell formation.

Top food sources:  Wheat germ, spinach, broccoli, boiled lentils, boiled chickpeas, peanuts, sprouts, asparagus, sesame seeds, hazel nuts, cashew nuts, cauliflower, walnuts, avocados.

Deficiency symptoms:  Anaemia, eczema, cracked lips, prematurely greying hair, anxiety or tension, poor memory, lack of energy, poor appetite, stomach pains, depression.

Promoters:  Works with other B-complex vitamins especially B12, so best to supplement with the whole complex, and should ideally be taken with food.

Adversaries:  High temperature, light, food processing, birth control pill.

RDA:  200 mcg (Toxicity on higher doses has rarely been reported, but there has been a small occurrence of gastrointestinal and sleep problems on doses above 15 mg (15000 mcg).

The DailyBurn.com says that Folic Acid is the synthetic form used in supplements and fortified foods like cereal and bread, and that the real name is Folate or Vitamin B9  They go on to say that “Studies suggest folate may help keep depression at bay and prevent memory loss. This vitamin is also especially important for women who are pregnant since it supports the growth of the baby and prevents neurological birth defects.  Get it from: Dark leafy greens, asparagus, beets, salmon, root vegetables, milk, bulgur wheat, beans.”

Biotin

Andrew Weil, MD, says that this is Vitamin B7, and helps support adrenal function, helps calm and maintain a healthy nervous system, is necessary for key metabolic processes, and is essential for the metabolism of carbohydrate and fat.

Livestrong.com says that “Taking a supplement that contains all the B-complex vitamins, including biotin, helps ensure that your body has the nutrients it needs to make energy. The B-complex vitamins work together to help your body metabolize carbohydrates, proteins and fats, so that your cells can use them as sources of energy.  Biotin, specifically, plays a key role in carbohydrate metabolism.”

Effective for:  Helping the body use essential fats, assisting in promoting healthy skin, hair, and nerves.  Particularly important in childhood.

Top food sources:  Cauliflower, peas, lettuce, tomatoes, oysters, grapefruit, watermelon, sweetcorn. cabbage, almonds, cherries, herrings, milk, eggs.

Deficiency symptoms:  Dry skin, poor hair condition, prematurely greying hair, tender or sore muscles, poor appetite or nausea, eczema or dermatitis.

Promoters:  Works with other B vitamins, magnesium and manganese.  Best supplemented as part of B complex with food.

Adversaries:  Raw egg white, which contains avidin (but this is not significant in cooked egg whites), and fried food.

RDA: 150 mcg

Livestrong.com also has this to say about blood and nerve health:
“Biotin and the other B-complex vitamins support the health of nerves and blood cells. Niacin, vitamin B6 and vitamin B12 all help synthesize red blood cells, the specialized cells that bind to the oxygen you inhale, and distribute it to tissues throughout your body. Low biotin levels also interfere with oxygen transport and cause anaemia.  The B-complex vitamins, including thiamine and B12, also promote healthy nerve and brain function. Low levels of certain B-vitamins harm the nervous system – for example, a B-12 deficiency can cause nerve damage.”
They also note that “Too much vitamin B-5 can interfere with biotin absorption, but a B-complex vitamin has a balance of all the B-vitamins to prevent you from getting too much B-5.”
However, they add that “It’s better to get B-complex vitamins from foods. Meats, eggs, dairy, whole-grains, legumes, fruits and vegetables have a variety of B-complex vitamins, and if you include these in your diet you’ll likely meet your needs. Foods especially rich in biotin include eggs, nuts, mushrooms, bananas and cauliflower.”

Other contents listed on my bottle of complete vitamin B complex are:

Choline Bitartrate which upon further research turns out to sometimes be called B4, but this also relates to Adenine and Carnitine, according to Wikipedia, although I saw them also list other numbers for Carnitine.: (A promoter of Choline is B5, so they work together, and it’s needed to break down fat in the liver, move fat into cells, protect the lungs, and synthesise cell membranes in the nervous system.
Deficiency Symptoms include high blood cholesterol and fat, fatty liver, nerve degeneration, high blood pressure, atherosclerosis, senile dementia, and reduced resistance to infection.
You can obtain this from foods such as lecithin, eggs, fish, liver, soya beans, peanuts, whole grains, nuts, pulses, citrus fruits, wheat germ, and brewer’s yeast.)

Inositol which according to Wikipedia can also be called B8, but this also relates to adenosine monophosphate (AMP), also known as adenylic acid:  A promoter of Inositol is Choline, so they work together, and Inositol is needed for cell growth, the brain and spinal cord, and the formation of nerve sheath.  Also for maintaining healthy hair, reducing blood cholesterol, and it’s a mild tranquilizer.  
Deficiency symptoms include irritability, insomnia, nervousness, hyper-excitability, reduction in nerve growth & regeneration, and a low HDL level.  
You can obtain this from foods such as lecithin, pulses, soya flour, eggs, fish, liver, citrus fruits, melons, nuts, wheat germ, and brewer’s yeast.)

PABA (ParaAminoBenzoic Acid):  Livestrong.com says that “Sometimes, people refer to PABA as “vitamin Bx,” but it is not a true vitamin, according to the U.S. National Institutes of Health on its MedlinePlus website.” And it’s “often included in sunscreen products and other skin care items.”  
PABA is not considered an essential nutrient, as noted by the Beth Israel Deaconess Medical Center, or BIDMC. “It is usually present in supplements that contain B vitamins, because it is a component of folic acid, or vitamin B-9.  PABA is found in Brewer’s yeast, beef liver and other meat, eggs, milk, mushrooms, spinach, whole grains and molasses.”  Wikipedia lists PABA as B10, but says that Bx is an alternative name for both PABA and Pantothenic Acid.  It says that PABA is “a chemical component of the folate molecule produced by plants and bacteria, and found in many foods.”

According to Wikipedia “other substances once thought to be vitamins were given numbers in the B-vitamin numbering scheme, but were subsequently discovered to be either not essential for life or manufactured by the body, thus not meeting the two essential qualifiers for a vitamin. See section related compounds for more information.”  There is a long list of strange things there after you get past the first few, beyond even my curiosity at the moment.

Notes and conclusion from me:

You can see that many of these are crucial to the nervous system, spinal cord, brain, etc, which are obviously all crucial to brain function & mental health directly.  But also many of the other deficiency symptoms could be a likely factor in causing mental health issues, such as lack of energy, fatigue, insomnia, restlessness, anxiety, ongoing pain, and digestive issues (often including gut inflammation – which has other knock-on effects such as:  more deficiencies due to inability to absorb nutrients sufficiently, skin rashes, “brain fog”, and the possible triggering of autoimmune issues, all of which I have experienced myself.)   

Obviously if you have an allergy to something like wheat then do not consume any of the food sources that contain it, otherwise that in itself can cause the gut inflammation, brain fog, autoimmune chain to start up, and I can tell you that in itself is detrimental to mental health.  Brain fog can make you feel unable to do anything meaningful anymore, and gut issues can really wear you down too.  If the gut flora gets out of balance, the build up of bad bacteria can directly affect your state of mind, making you bad tempered, and prone to craving the foods they want (mostly sugar) rather than what would be better for you, which of course only makes the gut even more out of balance if you succumb!  

I had to mention the wheat allergy when I saw how many of the B vitamins have wheat listed as one of their possible food sources.  (Vitamin E supplements and skin creams can often be made from wheat too, but can be made from other sources.)  My doctors had no idea what was causing my symptoms so I figured it out for myself and after I cut wheat out of my diet I was a new person after 2 weeks!  I realise I always had an issue with wheat even as a kid, but as I got older my body was more and more overwhelmed by it.  Also, If your gut gets out of balance due to poor diet, or use of antibiotics (which kill the good bacteria along with the bad), or any of the above, then a good probiotic can help rebalance it (and quickly reduce the sugar cravings).  Also, I note that alcohol is listed as an adversary for most of the B vitamins, so it interferes with their absorption/function, plus it also contains a lot of sugar, and can often contain wheat (I’m okay with the odd beer if it is one made from barley instead of wheat).  

Another interesting one is how often the birth control pill is listed as an adversary for these B vitamins, and I already knew it was an adversary for other things too.  I wrote an article some years back about how depression, weight issues, and addiction could be at least partially caused by mineral imbalance – http://www.radiance-solutions.co.uk/articleseven.htm – I started the article by explaining the electrolytes in relation to cell function, and included this bit about magnesium – “Shortage of magnesium (known as “the great soother”) often means we seek other things to try to soothe us – like sugar, alcohol, or drugs.  Putting on weight or other effects of having too much sugar can cause depression, and so can feeling dependent on things like alcohol or drugs.”  Later in the article I included a bit about how the birth control pill (containing copper) may cause zinc deficiency, which can be particularly detrimental for girls at the age of puberty, possibly increasing the likelihood of co-dependent and addictive behaviours.  I see in my Nutritional Therapist course notes that zinc is also crucial for a healthy nervous system and brain, hormone control, growth and healing, and essential for constant energy.  It also lists a tendency for depression as one of the deficiency symptoms, along with frequent infections, and low fertility.  My course book also points out that “Copper/Zinc levels should be balanced”, and that wheat (even in a person without an allergy to it), oxalates, excess sugar, and copper are all adversaries to absorption of zinc, and that alcohol prevents uptake.  

I can see how many imbalances can quickly become vicious cycles as deficiency symptoms might often easily lead you to want more stuff like alcohol and sugar that then causes you to get even less of what you are lacking.  I guess that the moral of the story is that if you feel bad physically or mentally the last thing you need is sweet stuff or alcohol to drown your sorrows, you need to look to improving the diet first and foremost.  Make it a positive step to take care of yourself and don’t let anyone or anything stop you because you have to be fine in order to show up for anyone or anything else in life.

I note now that a sea salt spray I’ve been recently using for helping clear sinus infections also contains a fair bit of copper, so I might supplement a bit with zinc to see if that will help clear things up.  Sorry I’ve gone on a bit of a ramble here, but the trail of research just shows how much many different things are actually interlinked.

So to conclude, we can see that the B Vitamins are so absolutely crucial to our health, and some of that is particularly relevant to mental health.  Many of the deficiency symptoms, even those not directly linked to mental health, could certainly reduce your ability to cope.  We can also see that the B Vitamins work together, so it is best to not supplement with just one if you do supplement, take the whole complex ideally.  However it is still always preferable to eat a healthy diet to include some of the foods containing each of them.  Of course other vitamins, minerals, and substances are absolutely crucial to our health as well, but I think the Vitamin B Complex is particularly crucial to good mental health.  I think the essential fatty acids, or oils, are as well though, and I note that some of the vitamin B’s are promoters for these as well.

Happy Health to You.