Magnesium… You see it listed on dog food ingredient labels and it’s often reported on a patient’s blood work, but what does it do in the body? I confess that I had only the sketchiest of ideas; so I did some research. Here’s what I found.
Magnesium is classified as an essential macromineral. The word “essential” in nutritional circles simply means that the body cannot manufacture it (or manufacture enough of it) to meet the body’s needs. Therefore, it must be included in the diet in sufficient amounts to avoid deficiencies. Macrominerals—calcium, phosphorus, magnesium, sodium, potassium, chloride, and sulfur—are minerals (inorganic nutrients) that the body requires in relatively larger amounts than it does microminerals (e.g., iron, zinc, copper, manganese, iodine, and selenium).
According to Medline Plus:
Magnesium is needed for more than 300 biochemical reactions in the body. It helps to maintain normal nerve and muscle function, supports a healthy immune system, keeps the heart beat steady, and helps bones remain strong. It also helps regulate blood glucose levels and aid in the production of energy and protein.
Hypermagnesemia (too much magnesium in the body) is not a common problem for dogs, unless they are suffering from chronic kidney failure. If a dog ingests too much magnesium, healthy kidneys are extremely efficient at excreting the excess.
On the other hand, hypomagnesemia (too little magnesium in the body) is seen quite frequently in sick dogs. One study found that 33.6% of critically ill dogs and cats suffered from hypomagnesemia, which tends to develop when a dog has one of the following conditions:
Some types of liver disease
Treatment with insulin
Acute kidney failure
Chronic heart failure
Sepsis (an overwhelming bacterial infection)
Iatrogenic (the use of some types of IV fluids, diuretics, other drugs, etc.)
Hypomagnesemia is often accompanied by other mineral deficiencies, particularly low calcium and potassium levels. The clinical signs associated with these conditions include:
Poor appetite and digestive function
Abnormally strong reflexes
Abnormal heart rhythms
Keep in mind that a dog without any of these symptoms can still have hypomagnesemia. Blood tests for magnesium levels tend to be quite reliable in dogs, although some individuals with normal blood levels (especially low-normal levels) might be whole body magnesium-deficient.
Treatment is simple and involves some form of supplementation—intravenous infusions when a dog’s condition is critical, oral when it is less so. Commercially available dog foods contain enough magnesium for healthy dogs, but if your dog is sick with one of the conditions listed above, magnesium supplementation might be a good idea to prevent or treat hypomagnesemia. The only time that I would worry about giving a dog a magnesium supplement is when he or she is at risk for chronic kidney failure.
Talk to your veterinarian if you think your dog needs a magnesium supplement.
Dr. Jennifer Coates
Hypocalcemia and hypomagnesemia. Dhupa N, Proulx J. Vet Clin North Am Small Anim Pract. 1998 May;28(3):587-608.