Iron, Insulin, and Laminitis

Since this article appeared, and indeed long before it, the idea that too much iron could be harmful and that there is a connection between iron and insulin has generated an enormous push-back.

Iron in Horses

Most of the objections begin with statements to the effect that iron uptake from the intestinal tract is well-regulated and iron is not toxic to horses. However, dietary iron overload is well documented in humans, lab animals, and many zoo species when taken out of their native habitat (CLICK HERE, to read more).  Severe iron toxicity has also been demonstrated in foals and adult horses (CLICK HERE, to read more).

The point here is that it is indeed possible for iron to be over absorbed and be toxic, even fatal, to the horse. 

The connection between iron and metabolic syndrome is so strong in humans that a paper representing an international consensus statement was recently published (CLICK HERE, to read more). If you want to delve deeper, start with the Recommendations section which describes in part:

"In a large prospective cohort of middle-age healthy men conducted in South Korea, elevated serum levels of ferritin were independently associated with development of the metabolic syndrome during the 5-year follow-up period32. Furthermore, in a large prospective study on European cases of incident type 2 diabetes mellitus, increased serum levels of ferritin were associated with an increased risk of type 2 diabetes mellitus, even among individuals with no overt inflammation, liver disease, high alcohol consumption or obesity33."

Getting back to the horse paper linked above, rabid criticism centers around the themes iron does not cause laminitis and does not cause metabolic syndrome. There was even a paper published recently that stated Thoroughbreds fed high levels of iron do not develop metabolic syndrome.

The problem is that nowhere in our paper was it ever stated that iron caused metabolic syndrome or laminitis. What we said was 100% of the hyperinsulinemic horses from the ECIR group tested for iron were overloaded and when results from another study were reexamined we found significantly elevated ferritin (p = 0.05) in horses considered hyperinsulinemic by dynamic insulin testing compared to horses with a normal response. Our conclusion was simply:

"These results suggest the potential for iron overload in hyperinsulinemic horses, a feature documented in other species and should stimulate further study into the relationship between insulin and iron dysregulation in the horse."

Both hyperinsulinemia and iron overload are multifactorial conditions. It's not as simple as Strep causes Strep throat. You can't expect x units of change in insulin correlates to y levels of iron, or vice versa. What we do know is there is good evidence of a connection.


- Eleanor Kellon, VMD

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