The Nervous System · Part One · How It Is Built and Fueled
Lesson 15 / 61
The B-Vitamins and Cofactors: Active Forms, Transport, and Enzyme Saturation
Thiamine to cobalamin, plus magnesium, and the enzymes that empty first.
The B-vitamins are coenzymes, molecules an enzyme must hold before it can run its reaction. Thiamine, riboflavin and niacin each become a different active form inside the cell. Pyridoxine becomes pyridoxal 5'-phosphate, cobalamin becomes two coenzymes, and magnesium completes the ATP those reactions spend. Nervous tissue declares a shortfall first because it runs these enzymes closest to capacity. The Unified Model of Tone reads cofactor status as the share of enzyme already loaded, a quantity the body holds inside a defended band.
Active B1 form
Thiamine diphosphate, about 90 percent of whole-blood thiamine
Active B6 form
Pyridoxal 5'-phosphate, made by a riboflavin-dependent oxidase
Cofactors on the cycle
B1, B2, B3, pantothenic acid as coenzyme A, plus magnesium
Thiamine saturation assay
TPP effect 8.3 to 18.5 percent in healthy adults
B-vitamin
One of the water-soluble vitamins numbered B1 through B12. A protein carrying none of its coenzyme is an apoenzyme and does nothing at all. The loaded protein is a holoenzyme. The body keeps only small stores of these vitamins and recycles what it can, so supply has to be continuous and any failure of absorption declares itself within weeks to months.
Saturation and tone
Add the missing cofactor to a patient's own enzyme in a test tube and the activity jumps. The size of that jump is the unfilled share of the enzyme pool, and healthy people hold it inside a narrow band rather than at zero. The Unified Model of Tone treats that held share as reserve, the spare catalytic capacity a neuron keeps for a demand that has not arrived.
01Coenzyme, not fuel
A B-vitamin is a coenzyme, so a neuron needs only a trickle of it and stops without it
The B-vitamins are spent as catalysts and recovered, which is why daily requirements sit in milligrams while glucose is counted in grams. An enzyme without its coenzyme is an apoenzyme, a correctly folded protein that cannot run its reaction. Bind the coenzyme and the same protein becomes a holoenzyme and turns over continuously. Each vitamin carries a chemical group from one reaction to the next and returns for another pass.
The vitamin in food is a precursor. The cell builds the working molecule. Thiamine is phosphorylated to thiamine diphosphate. Riboflavin becomes flavin mononucleotide and flavin adenine dinucleotide. Niacin becomes NAD and NADP. Pantothenic acid becomes coenzyme A. Pyridoxine becomes pyridoxal 5'-phosphate. Cobalamin becomes methylcobalamin and adenosylcobalamin.
Conversion is nearly complete before the blood is even drawn. About 90 percent of the total thiamine in human whole blood is already thiamine diphosphate Lu 2008. Adults not taking supplements run a mean of 114 nmol/L, with a range of 70 to 179. A number that tight across a healthy population is a regulated quantity, not a passive reflection of last night's dinner.
Magnesium is part of the substrate, not part of the enzyme
Magnesium works differently from the vitamins beside it. It is the second most abundant intracellular cation after potassium and participates in over 600 enzymatic reactions de Baaij 2015. Its main role is to complete the substrate. In vitro, ERK2 must bind two magnesium ions to phosphorylate at a physiological rate. Isothermal titration calorimetry detected no binding of free ATP by that enzyme at all, which makes the magnesium-ATP complex the true substrate Waas 2003.
Every ATP figure in this library is therefore a magnesium-ATP figure. The pumps costed out on Mitochondria and ATP cannot spend a molecule with no magnesium bound to it. A neuron short of magnesium is short of usable ATP at the same measured concentration.
02Findings
What the research shows
Measured cofactor failures, and what each one costs the nervous system.
03Enzyme saturation
Cofactor status is the share of an enzyme population already loaded, and that share can be measured directly
Cofactor status is read as a ratio between two runs of the same enzyme, not as a concentration in plasma. Hemolyzed whole blood is incubated with ribose-5-phosphate to read transketolase activity, then incubated again with thiamine pyrophosphate added to the tube. The rise between the two runs is the TPP effect, and it reports how much of that enzyme pool was sitting empty.
Healthy people are not fully loaded. In one healthy group the mean TPP effect came out at 13.5 percent, spanning 8.3 to 18.5 percent, while patients with Wernicke encephalopathy ranged from 28 to 67 percent Boni 1980. Obese women on an energy-restricted diet fell between them at 12.7 to 30 percent. The assay repeats well, with a coefficient of variation of 9.6 percent across TPP effects of 6 to 22 percent.
Riboflavin is read the same way, through the stimulation of erythrocyte glutathione reductase by added flavin adenine dinucleotide. Malaysian women averaged an activation coefficient of 1.49 plus or minus 0.17 against 1.38 plus or minus 0.11 in Canadian women Aljaadi 2019. Against a deficiency threshold of 1.40, that put 71 percent of the Malaysian sample and 40 percent of the Canadian sample below par.
A normal blood level and an empty enzyme are different findings
The two readings come apart routinely. Among Cambodian women, 39 percent in Phnom Penh and 59 percent in Prey Veng were thiamine insufficient by erythrocyte thiamine diphosphate Whitfield 2015. Suboptimal riboflavin status reached 89 and 92 percent in those groups, and 70 percent in a Vancouver comparison sample. A functional assay found a shortfall in a Canadian group that no clinical picture had flagged.
The Unified Model of Tone makes a claim about that gap. The quantity the body defends is not the vitamin in the plasma but the loaded share of the enzyme pool, and the unfilled remainder is reserve rather than failure. A person with a TPP effect of 14 percent has spare catalytic capacity available the moment demand rises. A person at 40 percent is already spending everything the enzyme can deliver, and the next demand has nowhere to come from.
The model stakes something checkable on that reading. Saturation and activity are meant to be one fact seen twice. Refill the enzyme until the activation coefficient comes back inside 8.3 to 18.5 percent, and the reaction rate has to come back with it, with blood lactate falling as pyruvate re-enters the cycle. An enzyme pool whose turnover returns as the activation coefficient comes back inside that band confirms the claim. Cofactor status is checked before any input is chosen, because an empty enzyme cannot answer one, and where that check sits in the order is set out on The Four Neurochemical Priorities.
04Thiamine-dependent enzymes
Thiamine deficiency stalls the enzymes that feed the citric acid cycle, and the lesion lands where they are worked hardest
Thiamine diphosphate serves pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase and transketolase. Alpha-ketoglutarate dehydrogenase is a rate-limiting enzyme of the tricarboxylic acid cycle, so losing its cofactor throttles the cycle at a single turn Butterworth 2009. End-stage chronic liver failure depletes liver thiamine stores and reduces that enzyme's activity, which is one reason ammonia-lowering treatment leaves some neuropsychiatric signs behind.
The enzyme loss is measurable in autopsied human brain. In Alzheimer brains the alpha-ketoglutarate dehydrogenase complex ran more than 75 percent below control and transketolase more than 45 percent below Gibson 1988. The deficits appeared in histologically undamaged regions as well as damaged ones. Small transketolase abnormalities showed up in red cells and cultured fibroblasts from the same patients, which puts the defect in the chemistry rather than in the tissue that died.
Supply is not the only way activity is lost. Peroxynitrite inactivated purified alpha-ketoglutarate dehydrogenase in a dose-dependent way by nitrating specific tyrosine residues, and glutathione restored the activity by removing those nitrations Shi 2011. Raising cellular glutathione in peroxynitrite-treated N2a cells returned the complex to control activity. The enzyme sits at a settable level that oxidative state moves in both directions.
The lesion picks an address
Thiamine deficiency does not damage the brain evenly. In the pyrithiamine-induced rat model of Wernicke encephalopathy the thalamic nuclei take the lesion, and the proposed mechanism combines impaired energy metabolism with converging glutamate inputs Langlais 1995. Reduced alpha-ketoglutarate dehydrogenase activity in autopsied human Wernicke brain and in pyrithiamine-treated rats is followed by focal lactic acidosis, increased glutamate release and depolarization Hazell 1998. The downstream injury runs through the pathway described on Excitotoxicity.
Clinically the deficiency hides. Across 131 cases of the Wernicke-Korsakoff complex diagnosed at necropsy, only 16 percent had shown the classic clinical triad and 19 percent had no documented clinical signs at all Harper 1986. A separate necropsy series had found that 80 percent were never diagnosed during life. A cofactor failure with a named lesion and a cheap treatment is missed because the enzyme fails before the syndrome assembles.
Lactate is the bedside signal
Among 270 critically ill patients admitted with COVID-19, 15.6 percent were thiamine deficient in the first hours in intensive care Gonçalves 2021. Thiamine correlated negatively with arterial lactate at r = -0.711 in the patients with diabetes and r = -0.489 in those without. Diabetes raised the odds of deficiency more than fourfold, at 4.28 with a 95 percent confidence interval of 2.08 to 8.81. When the cofactor runs out, pyruvate cannot enter the cycle, and the lactate on the chart is the reaction that could not proceed.
Infants show the sharpest version. In northern Laos, 54 infants presented with acute severe cardiac failure attributed to thiamine deficiency, 49 of them recovered after parenteral thiamine and 3 died Barennes 2015. In the same villages 50 of 468 live-born infants died in the first year, and verbal autopsy attributed 17 of those deaths to suspected infantile thiamine deficiency. One missing coenzyme, delivered by injection, separated recovery from death.
05Transport sets the ceiling
Cofactor supply into the brain is a gated flux, and the gate saturates far below what a supplement delivers
Thiamine reaches the brain on carriers that are already running near their working rate. In rats, thiamine monophosphate entered cerebellum, cortex, pons and medulla by a saturable mechanism Patrini 1988. Maximal transport ran 27 to 39 pmol per gram per minute, with half-saturation at 2.6 to 4.8 micromolar. At physiological plasma concentrations the actual rate was 2.06 to 4.90 pmol per gram per minute, a small share of that capacity.
The carrier is specific enough to be jammed. Pyrithiamine, thiamine disulphide and acetylthiamine all inhibited thiamine flux across the rat blood-brain barrier by competing for the saturable component, while oxythiamine did not affect it despite close chemical similarity Greenwood 1985. That selectivity is why pyrithiamine plus a deficient diet produces central deficiency signs quickly in rats and why the same trick does not work with every analogue.
Saturation shows up in people as a plateau. Across 127 healthy young adults, ten times the recommended daily dose of nine vitamins ran against placebo for a year Benton 1995. Blood status reached a ceiling after three months and went no higher for the remaining nine. Better attention scores appeared in the women taking the supplement, and improved thiamin status tracked improved performance across several cognitive measures.
The transporters have names and diseases
SLC19A2 encodes thiamine transporter-1, the first mammalian thiamine transporter identified, and its loss produces thiamine-responsive megaloblastic anemia with diabetes and deafness Fleming 1999. Pharmacological thiamine corrects the anemia and sometimes the diabetes, while the sensorineural deafness does not reverse. One carrier defect, three organs, and only two of them recoverable.
Its neighbor SLC19A3 encodes a related carrier. Missense mutations there cause biotin-responsive basal ganglia disease, a childhood encephalopathy that progresses to cogwheel rigidity, dystonia and quadriparesis, with bilateral necrosis in the head of the caudate on imaging Zeng 2005. Symptoms disappear within a few days on biotin at 5 to 10 mg per kilogram per day. A transport defect answers to flooding the gate.
Scarcity is answered by recycling
Biotin is the coenzyme for five carboxylases in mammals, and biotinidase is the enzyme that strips it back off lysine so it can be used again Zempleni 2008. In five children with late-onset multiple carboxylase deficiency, serum biotinidase ran at 0 to 3 percent of the mean control activity of 5.80 nmol per minute per milliliter Wolf 1983. Their parents sat at 46 to 65 percent. Children who cannot recycle biotin depend entirely on what arrives from outside. The body's defense against cofactor scarcity is recovery and reuse, not a large store.
06Pyridoxal phosphate
Pyridoxal 5'-phosphate runs the decarboxylases that build transmitters, and part of that enzyme pool is held unloaded as reserve
Pyridoxal 5'-phosphate is the busiest coenzyme in amino acid chemistry. In many free-living prokaryotes almost 1.5 percent of all genes code for PLP-dependent enzymes, and the share falls in higher eukaryotes Percudani 2003. Catalytic promiscuity extends the reach further. A single PLP enzyme can run more than one reaction, so an organism holds more PLP-dependent activities than it has genes for them.
In the nervous system those reactions include the decarboxylations that create transmitters. GABA is made from glutamate by two glutamate decarboxylase isoforms, GAD65 and GAD67, and the isoforms differ in how saturated they are with cofactor Kash 1997. The transmitter chemistry itself is set out on GABA, Glutamate and the Balance.
Unloaded enzyme is the reserve
Mice lacking GAD65 look normal at rest. Basal brain GABA and holo-GAD activity are normal, and what is significantly reduced is the pyridoxal 5'-phosphate-inducible apoenzyme reservoir, the pool of enzyme waiting unloaded Kash 1997. Those mice develop spontaneous seizures, and the seizures can be precipitated by fear or mild stress. Losing the empty fraction costs nothing at baseline and everything under demand, which is the clearest experimental picture of reserve in this chemistry.
The cofactor can be destroyed rather than missing
Pyridoxine-dependent seizures come from mutations in ALDH7A1, which encodes antiquitin Mills 2006. The substrate that accumulates, delta-1-piperideine-6-carboxylate, inactivates pyridoxal 5'-phosphate by forming a Knoevenagel condensation product with it. Intake is normal, absorption is normal, and the coenzyme is chemically consumed inside the cell. Urinary alpha-aminoadipic semialdehyde confirms the diagnosis.
Inflammation moves the reading too. Across 68 patients with stage 2 to 5 chronic kidney disease and 68 on hemodialysis, plasma pyridoxal 5'-phosphate correlated inversely with C-reactive protein at a partial rs of -0.21 Chen 2017. Homocysteine showed no significant correlation with any inflammatory marker in the same patients. A low PLP can report the state described on inflammation rather than a thin diet.
Excess injures the same neurons as deficiency
Seven adults developed ataxia and severe sensory nervous system dysfunction after daily high-level pyridoxine intake, four of them severely disabled, and all improved after withdrawal Schaumburg 1983. Weakness was not a feature and the central nervous system was clinically spared, which localizes the injury to the sensory neurons and their ganglia. Deficiency of B6 causes seizures and excess causes a sensory neuronopathy, so the healthy value is a band with an injury waiting on each side of it.
07Cofactors gate each other
One cofactor decides how much of another the body can activate, so a single-nutrient reading misses the failing step
Riboflavin controls vitamin B6 status. Pyridoxine is converted to pyridoxal 5'-phosphate by a flavin-dependent oxidase, so the B6 reading depends on the B2 supply. Across 407 healthy adults aged 18 to 92 who took no B-vitamin supplements, the riboflavin activation coefficient predicted plasma PLP at P = 0.019 Jungert 2020. Dietary B6 intake, age and body mass index were among the other determinants.
The gradient is stepwise. Plasma PLP fell from optimal riboflavin status through low to deficient at P = 0.001, independent of how much vitamin B6 the person ate Jungert 2020. Deficient riboflavin status covered 37 percent of that sample. Someone eating adequate B6 can read low on B6 because their riboflavin is short. Treating the number rather than the network moves nothing.
The same coupling reaches the blood. Across 416 women, those whose riboflavin activation coefficient sat at or above 1.40 were twice as likely to be anemic Aljaadi 2019. The adjusted odds ratio was 2.38, with a 95 percent confidence interval of 1.08 to 5.27. What a fall in carrying capacity does to the brain is counted on Oxygen, Red Cells and Anemia.
Loading a cofactor can restart the machinery it serves
Fifteen patients from 11 pedigrees had riboflavin-responsive multiple acyl-CoA dehydrogenation deficiency, and all of them carried mutations in the gene for electron transfer flavoprotein-ubiquinone oxidoreductase Olsen 2007. Riboflavin corrected their clinical and biochemical abnormalities wholly or partly. In one patient the deficiencies of flavin-dependent acyl-CoA dehydrogenases and respiratory chain complexes were mostly restored to control levels. Loading a flavoprotein with its cofactor rescued enzymes a mutation had destabilized.
Loading has a ceiling in the other direction. Sixty milligrams of tryptophan is conventionally equivalent to 1 milligram of nicotinamide in humans, and the conversion ratio is changeable Fukuwatari 2007. In six young women, nicotinamide supplements up to 562 micromol per day raised urinary nicotinamide metabolites linearly and left every intermediate of de novo synthesis unchanged. A pathway that is already met absorbs extra input without altering what it makes.
Niacin is the one coenzyme on this list the body can also build for itself. It makes nicotinamide from tryptophan through the kynurenine intermediates, starting from the same amino acid that Serotonin and the Gut-Brain Link begins with. What an axon does with its NAD once it has it belongs to Fuel Failure and Degeneration.
Coenzyme A failure has an imaging signature
Pantothenic acid becomes coenzyme A through pantothenate kinase, and PANK2 is the isoform that fails in pantothenate kinase-associated neurodegeneration Zhou 2001. Across 123 patients from 98 families, every classic early-onset case and one third of atypical cases carried PANK2 mutations Hayflick 2003. T2-weighted MRI showed hyperintensity inside the hypointense medial globus pallidus in every mutation carrier and in nobody else. A single step in coenzyme A synthesis writes dystonia and parkinsonism into the basal ganglia.
08Magnesium and the panel
Magnesium works from inside the channel, and the shape of a shortfall names the reaction that slowed
Cobalamin is the outlier in this group. It is activated into two coenzymes serving two compartments, methylcobalamin for methionine synthase in the cytosol and adenosylcobalamin for methylmalonyl-CoA mutase in the mitochondrion. It also injures nerves while the blood count reads normal, in 28 percent of 141 consecutive cases Lindenbaum 1988. The enzymes, the markers and the one-carbon traffic behind that are worked through on Methylation, Folate and MTHFR.
Magnesium sits in the channel
Magnesium blocks the NMDA receptor from inside the pore, and the block is voltage dependent. In mouse central neurones under patch clamp, glutamate and NMDA opened cation channels whose properties were voltage independent in magnesium-free solution Nowak 1984. Restore magnesium near its physiological level of about 1 mM and single-channel currents at resting potential are chopped into bursts. Opening probability falls, and both effects steepen as the cell hyperpolarizes.
The same block shows at the level of the whole cell. In hippocampal granule cells and CA1 pyramidal neurones in slices, NMDA lowered input resistance without magnesium and appeared to raise it with magnesium present Crunelli 1984. A depolarized or energy-starved membrane relieves the block, which is why magnesium standing guard at the pore and ATP holding the resting potential are the same protection read twice.
Reading the panel as a pattern
Because each cofactor occupies a different named step, the shape of a shortfall says which reaction slowed rather than which pill is missing. A rising lactate points at the thiamine-dependent dehydrogenases, which is why thiamine tracked arterial lactate at r = -0.711 in critically ill patients with diabetes. A low pyridoxal 5'-phosphate in someone eating adequate B6 points at riboflavin, whose status moved plasma PLP stepwise at P = 0.001. Sensory loss on its own points at either edge of the B6 band.
The chemistry is also open at the other end. Benfotiamine, a thiamine derivative, extended lifespan and reduced neurofibrillary tangles in P301S tauopathy mice Tapias 2018. Its metabolites rather than thiamine itself activated the Nrf2 antioxidant response, so the molecule chosen matters as much as the vitamin it came from.
Every shortfall in this lesson was a proportion rather than an absence. Transketolase sits 13.5 percent unfilled in healthy adults and 28 to 67 percent unfilled in Wernicke encephalopathy, and one assay reads both. What a clinic sees as beriberi, as a seizure arriving with mild stress, or as a sensory neuronopathy is that proportion pushed off its band in one direction or the other.
A cofactor is not a level in the blood. It is the share of your enzymes that can still run.
09Tone
How this system expresses tone
Tone in this chemistry is the loaded share of an enzyme population, held inside a band and reported by an activation coefficient. That share moves with supply, with transport, and with what the last week of demand asked the enzyme to do.
Set point
Whole blood holds thiamine diphosphate at 70 to 179 nmol/L in unsupplemented adults, and roughly 90 percent of total thiamine sits in that single active form.
Constraint
Thiamine transport into rat brain saturates, with half-saturation at 2.6 to 4.8 micromolar, so intake beyond the carrier's capacity changes nothing downstream.
Gain
GAD65 knockout mice keep normal resting GABA but lose the PLP-inducible apoenzyme reserve, and seizures then follow fear or mild stress.
Oscillation: the citric acid cycle is a loop with a rate-defining turn at alpha-ketoglutarate dehydrogenase, so a missing coenzyme sets how fast the loop comes back around. Load: 15.6 percent of critically ill patients admitted with COVID-19 were thiamine deficient, and arterial lactate rose as thiamine fell at r = -0.711 in those with diabetes. Time course: blood status in adults taking ten times the recommended dose of nine vitamins plateaued at three months and rose no further for the remaining nine. Coupling: riboflavin status predicted plasma pyridoxal 5'-phosphate independent of B6 intake across 407 adults, which makes two vitamins one measurement. Prediction: the liver holds the thiamine store the brain draws on, and liver failure empties it before any dietary change occurs. Input quality: 60 milligrams of tryptophan substitutes for 1 milligram of nicotinamide, so what arrives decides which pathway supplies the coenzyme.
10Across the library
How this page relates to the rest of the library
The fuel these coenzymes process. What arrives at the neuron, how little is stored, and why signaling fails before structure does.
The machinery the cofactors serve, from acetyl-CoA to the proton gradient, and the reason every ATP figure is really a magnesium-ATP figure.
The one-carbon half of cobalamin, where methylcobalamin and folate meet and homocysteine reports the traffic.
Where a cofactor shortfall ranks among the things checked before any input is chosen, and why that order decides what is addressed first.
What follows when the magnesium block is relieved and glutamate signaling passes from message into injury.
Where riboflavin status meets hemoglobin, and what a fall in carrying capacity does to the tissue with the highest demand.
11Frequently asked
Questions about this topic
What do B-vitamins actually do in the nervous system?
B-vitamins are coenzymes. Each one is a small molecule an enzyme has to be holding before it can run its reaction, and none of them is burned for energy. Thiamine becomes thiamine diphosphate for two dehydrogenases and transketolase. Riboflavin becomes FMN and FAD. Niacin becomes NAD. Pantothenic acid becomes coenzyme A. Pyridoxine becomes pyridoxal 5'-phosphate for the decarboxylases that build transmitters. Cobalamin becomes methylcobalamin and adenosylcobalamin. Nervous tissue notices a shortfall first because it runs these enzymes closest to their capacity.
Can a blood test miss a B-vitamin problem?
It can, because a plasma level and a working enzyme are different measurements. The functional assay runs a patient's own enzyme twice, once alone and once with the cofactor added in the tube, and the rise between them reports how much of the enzyme pool was sitting empty. Healthy adults show a thiamine pyrophosphate effect of 8.3 to 18.5 percent, while Wernicke encephalopathy ranges from 28 to 67 percent. Riboflavin is read the same way through erythrocyte glutathione reductase, with 1.40 marking deficiency.
Why does thiamine deficiency damage specific parts of the brain?
Because thiamine diphosphate serves alpha-ketoglutarate dehydrogenase, a rate-limiting enzyme of the citric acid cycle, and the lesion lands where that enzyme is worked hardest against converging excitatory input. In the pyrithiamine rat model the thalamic nuclei take the damage, and the sequence runs from reduced enzyme activity to focal lactic acidosis, increased glutamate release and depolarization. In people the corresponding lesions sit in diencephalic and brainstem structures, chiefly the medial thalamus. Only 16 percent of necropsy-confirmed Wernicke-Korsakoff cases had shown the classic clinical triad in life.
Can you take too much vitamin B6?
Yes, and the injury has a recognizable shape. Seven adults taking daily high-level pyridoxine developed ataxia and severe sensory nervous system dysfunction, four of them severely disabled, and all improved after they stopped. Weakness was not a feature and the central nervous system was clinically spared, which places the damage in the sensory neurons and their ganglia. B6 deficiency causes seizures and B6 excess causes a sensory neuronopathy, so the healthy value sits inside a band with an injury waiting on either side.
Can a genetic disorder be treated with a vitamin?
Several can, because a large dose can drive a step that a mutation left barely working. Loss of the SLC19A2 thiamine transporter causes megaloblastic anemia with diabetes and deafness, and pharmacological thiamine corrects the anemia and sometimes the diabetes while the deafness stays. Mutations in the neighboring SLC19A3 carrier cause biotin-responsive basal ganglia disease, whose symptoms disappear within days on biotin at 5 to 10 mg per kilogram per day. Pyridoxine-dependent seizures answer to B6 because the mutation consumes the coenzyme rather than blocking its supply.
What does magnesium do at the synapse?
It sits inside the NMDA receptor pore and blocks it in a voltage-dependent way. In mouse central neurones under patch clamp, glutamate and NMDA opened channels with voltage-independent properties in magnesium-free solution. Magnesium near its physiological level of about 1 mM chopped those currents into bursts and lowered the probability of opening. Depolarization relieves the block, which is how a depolarized or energy-starved membrane loses the guard. Magnesium also completes the substrate for ATP-using enzymes, since a kinase binds the magnesium-ATP complex rather than free ATP.
Do B-vitamin supplements help someone who is not deficient?
The pathways behave as though already met. Across 127 healthy young adults taking ten times the recommended daily dose of nine vitamins for a year, blood status reached a ceiling after three months. In six young women, nicotinamide up to 562 micromol per day raised urinary metabolites linearly while leaving every intermediate of de novo synthesis unchanged. Where a genuine shortfall exists the picture reverses, as in the riboflavin-responsive enzyme deficiency that corrected on treatment. A replete pathway absorbs extra input without changing what it makes.
Are B-vitamin deficiencies still common?
They are, and functional assays keep finding them where diets look adequate. Among Cambodian women, 39 percent in Phnom Penh and 59 percent in Prey Veng were thiamine insufficient, and suboptimal riboflavin status reached 89 and 92 percent. Deficient riboflavin status covered 37 percent of 407 healthy unsupplemented adults aged 18 to 92. Illness raises the rate again. Among 270 critically ill patients admitted with COVID-19, 15.6 percent were thiamine deficient, and diabetes raised the odds of deficiency more than fourfold.
12The sources
References
Sources: primary literature, linked inline.