Great hopes were pinned on doctors in the eighties of the last century: it was believed that B vitamins reduce the content of homocysteine in the blood — an amino acid, a high level of which is directly associated with heart and vascular diseases.
Many studies have been conducted in different countries, and as a result, the effectiveness of these vitamins was recognized as ambiguous: "50-50".
Indeed, when patients take more effective medications, "vitamins" play only an auxiliary role. But doctors continue to prescribe them for various cerebrovascular pathologies (diseases of the brain vessels). Additional help to the body is not a hindrance, right?
Yes, modern, effective and inaccessible to most patients due to their high price, drugs act much faster. And of course, "vitamin therapy" is not so effective. But almost all drugs have a "dose-dependent "(the higher the dosage, the better) and "chrono-dependent " (the longer the drug is taken, the longer the positive dynamics persists) effect.
At the same time, the undeniable advantage of vitamins is the price. The doctor, prescribing the drug, can be sure that the medicine will be taken as much as necessary, and will not empty the patient's wallet. Many doctors, when prescribing group B, are guided by this.
Types of Vitamin B and Their Benefits
You know the main B vitamins for sure. These are the well-known B1, B6 and B12:
(pyridoxine) strengthens the immune system, has a beneficial effect on skin diseases, and restores the nervous system. According to some reports, 80 mg of vitamin B6 per day reduces the risk of myocardial infarction by 32%. 
(cyanocobalamin) has a beneficial effect on the function of the liver and nervous system, and participates in the restoration of metabolism. In the treatment of chronic fatigue syndrome, vitamin B12 is effective in 50-80 % of people. 
But their less famous counterparts also deserve attention:
(folic acid, folacin, vitamin Bc) is extremely important for the development of the brain and nervous system of the embryo, it is also necessary for the development of a breastfed child, and adults primarily for the normal functioning of the nervous system. 
B vitamins are indispensable for diseases of the nervous system.
Once the head aches, then the irritability has increased, then the back has been "shot", then there are problems with memory… B vitamins are called "neurotropic" because of their effect on the functions of nerve cells.
Currently, more than a hundred studies have been published that have shown clinical improvement in the use of B vitamins in patients with pain syndromes.
When do B vitamins help?
Especially often, vitamins of this group are prescribed to patients with back pain. Why?
Because it has been repeatedly proven that these "magic" vitamins have an effect on nerve cells that go from sensitive receptors to the brain, as if "slowing down" pain impulses.
If the nerve fiber is damaged, consisting of hundreds and thousands of processes of neurons (nerve cells), then for their successful "restoration" the same vitamins are needed that work, laying proteins like bricks, to recreate the fiber shell.
However, many neurologists remain skeptical about their therapeutic capabilities, believing that in many cases there is a placebo effect.
The fact is that when prescribing vitamins alone, no one has ever managed to achieve a 100% effect in treatment. Therefore, if you have back pain, consult a doctor that will choose the right combination of medicines for you, including the B-complex.
In 2000 and 2002, the American Association of Psychiatrists published research results in the American Journal of Psychiatry, proving the effect of vitamin B12 deficiency on the appearance of clinical depression in elderly patients. Many of them were not shown antidepressants, so vitamin complexes paired with diet and gymnastics gave good results. [9, 10]
Taking into account these data, many doctors began to actively prescribe B-complexes for the treatment of depression and achieve an effect. The results of other studies have shown that the use of foods rich in folic acid by pregnant women, or taking adequate doses of folic acid and vitamin B12 significantly reduces the risk of developing neural tube laying defects. This is also the "gold standard" of pregnancy management all over the world.
And B1 deficiency also plays an important role in the development of alcoholic polyneuropathy, which is one of the most common forms of generalized peripheral nerve damage in Russia.
The only questionable purpose of B vitamins is still asthenic conditions, such as the notorious "chronic fatigue syndrome".
Too many diseases can be hidden under the mask of this seemingly innocent diagnosis. The person is tired... stress, lack of sleep and irregular nutrition have done their dirty work. Drink some vitamins – and everything will pass? And they drink after all! By handfuls and kilograms!
...And we are at risk of overdose
When using excessive doses (three or more times higher than the recommended daily intake) of B vitamins, intoxication develops.
Hypervitaminosis of vitamins B1, B2 and B6 can cause fatty liver dystrophy.
Among the elements of group B, the most toxic are B6 and B12. And allergic reactions are observed mainly with an overabundance of them, as well as with an overdose of vitamins B1 and B2.
So, an overabundance of vitamin B1 causes symptoms in the form of allergic reactions and spasmodic headaches. Blood pressure decreases, fever appears, weakness, nausea, vomiting may occur, chills are replaced by a feeling of heat, tinnitus worries, severe sweating and dizziness appears.
With prolonged use of vitamin B6 in excess dosages, anemia develops, coordination of movements is disrupted and numbness of the limbs appears.
Excess vitamin B12 leads to heart failure, pulmonary edema, vascular thrombosis due to increased blood clotting and anaphylactic shock. The heart rate increases, there are pains in the heart area, nervous disorders increase, allergic rashes appear on the skin in the form of urticaria.
As you can see, caution is needed even with such seemingly harmless drugs as vitamins. Therefore, it is better to consult a doctor for advice.
1. WebMD, Thiamine (Vitamin B1), retrieved from https://www.webmd.com/vitamins/ai/ingredientmono-965/thiamine-vitamin-b1
2. WebMD, Pyridoxine HCL, retrieved from https://www.webmd.com/drugs/2/drug-5427/pyridoxine-vitamin-b6-oral/details
3. WebMD, VITAMIN B-12, retrieved from https://www.webmd.com/drugs/2/drug-1010/cyanocobalamin-vitamin-b-12-oral/details
4. WebMD, Riboflavin, retrieved from https://www.webmd.com/vitamins/ai/ingredientmono-957/riboflavin
5. National Institutes of Health, Nicotinic acid, retrieved from https://pubchem.ncbi.nlm.nih.gov/compound/Nicotinic-acid
6. Harvard T.H. Chan School of Public Healt, Folate (Folic Acid) – Vitamin B9, retrieved from https://www.hsph.harvard.edu/nutritionsource/folic-acid/
7. Scott Buesing, Miranda Costa, Jan M. Schilling, Tobias Moeller-Bertram, Vitamin B12 as a Treatment for Pain, retrieved from https://pubmed.ncbi.nlm.nih.gov/30700078/
8. American Physiological Socie, B-vitamins prove effective in relieving chronic pain, retrieved from https://www.eurekalert.org/pub_releases/2003-04/aps-bpe040903.php
9. Gary Payinda, M.A., and Todd Hansen, B.A., Vitamin B12 Deficiency Manifested as Psychosis Without Anemia, retrieved from https://ajp.psychiatryonline.org/doi/10.1176/appi.ajp.157.4.660
10. Brenda W.J.H. Penninx, Ph.D., Jack M. Guralnik, M.D., Ph.D., Luigi Ferrucci, M.D., Ph.D., Linda P. Fried, M.D., Ph.D., Robert H. Allen, M.D., and Sally P. Stabler, M.D., Vitamin B12 Deficiency and Depression in Physically Disabled Older Women: Epidemiologic Evidence From the Women’s Health and Aging Study, retrieved from https://ajp.psychiatryonline.org/doi/full/10.1176/appi.ajp.157.5.715