During the course of normal digestion and metabolism, the calcium from the food the iguana eats is mixed with calcium mobilized (pulled by the body) from the bones. This mixture of dietary and bone-derived calcium is circulated throughout the body in the bloodstream. The calcium is used by many of the body's systems and cellular processes. The amount of calcium that was originally "borrowed" from the bones is returned to the bone to solidify the bone matrix.

When a diet high in calcium oxalates is fed, this last step fails to take place. Instead of all of the borrowed calcium being returned to the bones, it keeps circulating until it deposits itself into the soft tissues, eventually causing pain and organ dysfunction. The bones, continually stripped of calcium over time, become brittle and porous. They become so fragile that they are at high risk of breaking under the least pressure. Loss of bone density due to high a high oxalate intake is just one type of metabolic bone disease, MBD being an umbrella term that covers the different types of health problems caused by the different ways calcium in the body is affected by diet, age, and other factors.

Effects of MBD

In most forms of metabolic bone disease, the bones begin to look like sponges as the calcium is pulled out of the bone matrix. Swellings along the long bones and tail begin to appear as fibrous growths are formed around the bone to try to hold the weakened remnant of the bone together. The bones at this time are easily fractured. In advanced cases, the jaws become too soft and swollen for the animal to self-feed. Partial paralysis and tremors may set in, and the iguana becomes too weak to climb or even support its body on its legs.

Early on, when the telltale bumps are first felt along both the thighbones, there is time to reverse the condition by correcting the diet and ensuring proper access to ultraviolet B. If the diet and/or environment remain unchanged, however, or not corrected to the degree required, the disease will progress to the point were veterinary intervention will also be required. Radiographs may be needed to assess the degree of bone loss and locate any fractures that need setting and immobilization. A vitamin D3 injection may be required, as well as injections of calcium and prescription calcium supplements. A course of antibiotic therapy may be necessary, as may rehydration by injecting the appropriate fluids. All in all, it is much easier and cheaper (in the long run!) to feed the proper foods to begin with.

High Oxalate Plants

Oxalates and oxalic acid cause two main problems in iguanas. They bind with calcium, leading to metabolic bone disease.

They can also create tiny crystals that are deposited in soft tissues and in joint areas. If the soft tissues they settle in any of the organs that keep the body running, the organ function is impaired and eventually cannot adequately perform its job: it fails. If the crystals settle in muscle tissue or around joints, they cause pain and stiffness, both of which impair mobility.

Spinach, rhubarb, beets, parsley and chard are high in oxalate and/or oxalic acid.  We cannot avoid oxalates completely, as most leafy greens, and some vegetables and fruits, have at least some oxalate and/or oxalic acid. What we can do is make decisions to maximize the nutritional punch of the overall diet while minimizing as much as possible the amount of these potentially harmful plant chemicals.