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The MastAttack 107: The Layperson’s Guide to Understanding Mast Cell Diseases, Part 70

84. Is the problem for mast cell patients that they can’t break down histamine properly?

  • Not exactly. Mast cells that are overly activated will make and release more histamine but the activation comes before the histamine, not the other way around. There’s no evidence that indicates that in mast cell disease there is something wrong with the way the body breaks down histamine.
  • Histamine intolerance is not a well accepted diagnosis in the general medical establishment. Histamine intolerance is when patients react to foods and activities that contain or cause the production of histamine in the body. The general thinking on why this happens is that the body doesn’t make enough enzyme to break down the histamine at a normal rate. I have not seen convincing data that histamine intolerance is in fact due to the inability of the body to break down histamine fast enough. Regardless, I know a lot of people who feel better when they take DAO supplements or each DAO rich foods. DAO (diamine oxidase) is one of the enzymes your body uses to break down histamine.
  • Please keep in mind that histamine intolerance is a distinct phenomenon from mast cell disease. In mast cell disease, the problem is that the mast cells are too activated so they release excessive histamine into the body. In histamine intolerance, the mast cells are not overly activated, and the body can’t break down histamine fast enough. This means that even if a person with histamine intolerance makes a normal amount of histamine, their body can’t break it down at a normal rate.
  • It is theoretically possible to have both mast cell disease and histamine intolerance. There’s not a reliable way to test for histamine intolerance beyond symptoms, and there aren’t really robust diagnostic criteria. Some people with suspected mast cell disease test negative despite having mast cell symptoms and responding to treatment. This means that there’s no way to definitively know right now if a trigger causes a reaction because of histamine intolerance or a mast cell reaction beyond having a prior, firm diagnosis of mast cell disease.
  • There is something I find intriguing that may be linked to histamine intolerance. I mentioned diamine oxidase (DAO) above. It is one of enzymes your body uses to break down histamine. The other enzyme your body uses for this is called histamine n-methyltransferase. When this enzyme breaks down histamine, it produces n-methylhistamine.
  • N-methylhistamine is the most common breakdown product of histamine. It is also the molecule that we test for as part of the diagnostic workup for mast cell disease. The reason we test for n-methylhistamine instead of histamine is because histamine is broken down so quickly that n-methylhistamine stays in your body much longer than histamine. We use it as a surrogate marker for histamine since it’s easier to measure.
  • I know a lot of mast cell patients who have flagrant histamine symptoms that repeatedly have normal tests for n-methylhistamine both in blood tests and in 24-hour urine tests. There are a few reasons why this could be but I have started to wonder if the reason those tests come back normal is because your body doesn’t make enough of the enzyme that breaks down histamine in this way. As I said above, there is no real evidence to support this, just something I think about sometimes.


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