Even when taken in very high doses of 3–4 g, niacin is almost completely absorbed. Once absorbed, physiologic amounts of niacin are metabolized to NAD. Some excess niacin is taken up by red blood cells to form a circulating reserve pool. The liver methylates any remaining excess to N1-methyl-nicotinamide, N1-methyl-2-pyridone-5-carboxamide, and other pyridone oxidation products, which are then excreted in the urine. Unmetabolized nicotinic acid and nicotinamide might be present in the urine as well when niacin intakes are very high.
I vaguely remember this being the rationale behind taking TMG when supplementing with high dose niacin. IIRC there was evidence that TMG/betaine is in the pathway that is disrupted via high dose niacin (rather than B12 and other methyl donors)
1,000 to 2,000 mg is quite a normal dose and is good for the circulation and blood pressure as it's a vasodilator, to lower triglycerides, increase 'good' colesterol and reduce the 'bad' cholesteol and improve mental health. A way of lowering the requirement is to adopt a ketogenic diet.
Whether 1000 to 2000 mg is too much is a matter of opinion, but I would not claim that this dosage is 'normal.' The Recommended Dietary Allowances (RDAs) for niacin for adults is about 16 mg, which can easily be achieved with a normal diet. The Tolerable Upper Intake Levels (ULs) for Niacin is 35 mg. When the bioavailability of vitamin B3 is insufficient, it is often due to a deficiency of, yes, there they are again, B1, B2, and B6. Because deficiencies in these vitamins are particularly evident in those with PD, supplementation of all B vitamins with a B-complex is often more essential.
The Niacin Fact Sheet for Health Professionals is highly recommended:
From a subjective standpoint, since people have been taking 3000+ mg of Niacin for dislipidemia, it seems 100 mg per day I am taking is safe and not excessive, though I understand that it is still way above the RDA.
If you think that high dosages are better for you, then by all means go ahead. Just don’t claim that it’s ‘normal.’ My main concern here is the safe maximum dosage that we have collectively established, the ULs standard of 35 mg. You may find it nonsense, but I prefer to mention it for the sake of completeness.
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