I've only seen one published research study involving the relationship between cinnamon and histamine, and that study showed that cinnamon was effective in preventing excessive formation of histamine!
Certain foods do indeed have high histamine content. Histamine is a substance typically produced from the amino acid histidine. This amino acid is found in many protein-containing foods, especially if those foods have had time to age. When a food is high in the amino acid histidine and certain types of bacteria are given enough time to start metabolizing parts of the food, they can convert histidine amino acids found in the food's proteins into histamine. (In biochemical terms, they decarboxylate the histidine using a decarboxylase enzyme.)
Practically speaking, since this buildup of histamine from histidine in food can take a good bit of time, it is often aged, higher protein foods that contain larger amounts of preformed histamine. These foods can include fermented soybean products (like fermented soy sauce), many cheeses, and other fermented foods like sauerkraut. Aged meats can also contain higher amounts of preformed histamine. When fish starts to spoil—even before the signs of spoilage are detectable—there can be a buildup of histamine in the fish from this same bacterial process. For this reason, it's important to include the freshest of fish in your Healthiest Way of Eating if you are trying to avoid all preformed food histamines.
The histamine question gets more complicated, however, when you consider the digestion of any higher protein food. Certain bacteria found in the digestive tract can also take the histidine in any food and convert it into histamine. In other words, if a person does not have a fully healthy digestive tract, there is a chance that his or her body will end up with too much food histamine, not because that histamine is found preformed in food, but because the histidine amino acids in food are being converted into histamine inside of the digestive tract. In this case, avoiding high-histamine foods won't help a person nearly as much as restoring digestive vitality and digestive tract function.
In my book, The World's Healthiest Foods, I note that there are 160 milligrams of total protein in two teaspoons of ground cinnamon. I've been unable to find a breakdown of specific amino acids in cinnamon, but there would definitely be far lower than 160 milligrams of histidine in two teaspoons of cinnamon because there would be a pattern of various amino acids in this spice (like in every spice). For this reason, cinnamon would be an unlikely source for much histamine exposure (either preformed in the spice or formed upon breakdown in the digestive tract).
One nutrient that stands out in the histamine allergy research is vitamin B6. In the cells that line our digestive tract (and elsewhere in our body as well) there are enzymes called diamine oxidases. These enzymes can break down histamine into other substances before it gets absorbed into our bloodstream. They are also enzymes that require vitamin B6 to function. Making sure that you've got optimal B6 intake is one way to help lower the risk of histamine reaction in your body. In my book, you'll find a full profile of vitamin B6 and food that provide it in the greatest quantity.
For more information on this topic, please see:
Csaba G, Kovacs P, Tothfalusi L, et al. Prolonged effect of stress (water and food deprivation) at weaning or in adult age on the triiodothyronine and histamine content of immune cells. Horm Metab Res. 2005;37(11):711-5.
Oguri S, Enami M, Soga N. Selective analysis of histamine in food by means of solid-phase extraction cleanup and chromatographic separation. J Chromatogr A. 2007;1139(1):70-4.
Sato T, Horiuchi T, Nishimura I. Simple and rapid determination of histamine in food using a new histamine dehydrogenase from Rhizobium sp. Anal Biochem. 2005;346(2):320-6.
Wood JD. Histamine, mast cells, and the enteric nervous system in the irritable bowel syndrome, enteritis, and food allergies. Gut. 2006; 55(4):445-7.