This is because the enzyme that degrades adrenaline, the enzyme COMT, requires niacin as a cofactor. It actually requires two things: SAMe and niacin, and giving niacin helps with both of those things.
I think that some people here might be interested in knowing why, so I will explain, because I think it also explains one of the underlying contributors to adrenal fatigue and how people with adrenal fatigue can improve their condition even more by just taking niacin more than once a day. By the way, I think you should be able to get the same effect using niacinamide without getting the flush. I stumbled on to all this while I was leaning how to help my son with fatigue and depression.
You (this is a general you, not directed any specific person) have to ask yourself “Why do I have so much adrenalin?” Well, I think the reason is that you have histamine problems. Probably gut dysbiosis is the underlying cause and either gut bacteria are releasing histamine, especially when you eat, or leaky gut is causing food sensitivities causing a release of histamine, which may or may not give you obvious symptoms.
High histamine in the body requires high adrenaline to balance it, or your blood pressure would drop too low.
So why can't you get rid of the histamine so you don't need to make so much adrenaline?
There are two biological pathways to get rid of histamine. (And vitamin C gets rid of it for a little while if you take a ton of it.) The pathway that is designed only to get rid of histamine is the enzyme DAO, which is made in the gut and in other parts of the body. This pathway responds quickly to changes in histamine levels. The other pathway – methylation – does many things and responds quite slowly to changes in histamine. It takes a methyl group from SAMe and degrades the histamine with it. So if your DAO pathway is blocked, and you have to use the methylation pathway to get rid of histamine – your body can't adjust the levels of SAMe to the constantly changing amounts of histamine, and part of the time you don't have enough and part of the time you have too much SAMe. At night the SAMe levels rise as your histamine levels drop and the production of SAMe stays the same, leading to an excess of adrenaline which you can't get rid of because although you have enough SAMe, your niacin has been used up by the DAO pathway in trying to get rid of the histamine.
So you will probably be saying “What!”, niacin isn't a cofactor for DAO! DAO cofactors are Vitamin C, B6 and copper!” Well, that is true, but DAO is inhibited by its own product: imidazole acetaldehyde. Since the enzyme that degrades imidazole acetaldehyde, aldehyde dehydrogenase, requires NAD(P)+ (from niacin) to function, a shortage of niacin will lead to a feedback inhibition of DAO when the levels of imidazole acetaldehyde become too high. Magnesium may also be used as a cofactor in addition to niacin.
The niacin is needed for a step below the DAO step in the same pathway to get rid of histamine.
“Histamine can be metabolized by extracellular oxidative deamination of the primary amino group by diamine oxidase (DAO) (2) or intracellular methylation of the imidazole ring by histamine-N-methyltransferase (HNMT) (3). Therefore, insufficient enzyme activity caused by enzyme deficiency or inhibition may lead to accumulation of histamine. Both enzymes can be inhibited by their respective reaction products in a negative feedbackloop “
“The active site binds to one molecule of an aldehyde and an NAD(P)+ that functions as a cofactor. “
So a lack of niacin is not only preventing you from getting rid of adrenaline, it's preventing you from getting rid of all your excess histamine, which is probably why you have excess adrenaline in the first place. And your need to get rid of the histamine is draining your niacin levels. So if you take niacinamide 3 times a day instead of just at night, you might just keep your histamine levels down to where you don't have to produce so much adrenaline! And your SAMe levels will be much more stable through the day if your histamine levels are kept low and you won't need as many supplements for the methylation cycle, because your SAMe won't be getting used up getting rid of tons of histamine. And your adrenal glands would probably enjoy not having to make so much adrenaline to balance out the histamine, and after they get a good rest, they might not be so fatigued!
P.S. You might need some extra P5P (B6) and also a couple grams of vitamin C a few time a day because I can tell you from experience that it does not work without the vitamin C. (I mean he DAO pathway won't work without vitamin C, you will still get rid of adrenaline during the night without Vitamin C, because by then the histamine will be gone already by the time you feel the adrenaline. I guess that as long as the adrenaline is balancing the histamine, you don't really feel it because it isn't in excess until the histamine is gone.)