By Dr. Becker
It’s common knowledge that vitamin D is essential for proper functioning of the human heart, and research has found a direct link between vitamin D deficiency and congestive heart failure (CHF). The relationship is so strong, in fact, that vitamin D blood levels are used to predict the chances of survival of people with CHF.
The muscles and nerves of the body rely on precise levels of calcium in the blood to function correctly. Vitamin D plays a crucial role in maintaining those precise levels through regulation of calcium absorption from the intestines. In humans, vitamin D directly supports heart muscle electrical activity and muscle contraction.
Our canine companions also acquire heart disease, and congestive heart failure is a common cause of death in affected dogs. Canine heart disease is either acquired or congenital, with the vast majority of cases – about 95 percent – in the acquired category. It is estimated up to 60 percent of aging dogs have a heart problem.
What role, if any, vitamin D plays in canine heart disease has never really been investigated. But a new study conducted at Cornell University’s College of Veterinary Medicine and published recently in the Journal of Veterinary Internal Medicine1 sheds some light on the subject. The researchers determined that vitamin D may indeed play a role in congestive heart failure in dogs similar to the part it plays in human heart disease.
What the Cornell Study Revealed: Dogs with Congestive Heart Failure Have Abnormally Low Blood Levels of Vitamin D
The Cornell researchers compared blood levels of vitamin D in dogs with CHF and healthy dogs. The dogs with congestive heart failure had lower blood levels of vitamin D than the dogs without heart disease. The researchers also noted that, as with humans, low blood levels of vitamin D were linked to poor survival rates in the dogs.
Unlike humans who get vitamin D both from exposure to sunlight and through certain foods and dietary supplements, dogs don’t produce vitamin D in their skin, so diet alone must supply all their vitamin D requirements. Unfortunately, the Cornell study failed to demonstrate whether diet was a cause of vitamin D deficiency in dogs with CHF. Instead of analyzing the dogs’ diets, the researchers relied on information compiled from questionnaires, and also made various assumptions about approximate vitamin D intake.
The study also did not address other possible causes for vitamin D deficiency in the dogs with CHF. In humans, heart disease is linked to patient fitness levels and amount of body fat. Vitamin D is fat-soluble and can be isolated in body fat, reducing blood levels. All the dogs in the Cornell study had normal amounts of body fat, so no association between heart disease and body fat could be made.
Another piece of information missing from the Cornell study was whether the dogs with CHF were taking medications that might contribute to their low vitamin D blood levels. Diuretics, which are commonly used to treat heart disease in both humans and dogs, can cause the loss of chemicals in the blood through increased urination. The researchers didn’t evaluate whether the dogs in the study were excreting vitamin D in their urine, a situation that could contribute to a deficiency.
This study is the very first to examine the relationship between vitamin D and congestive heart failure in dogs. Much more research is needed, but what the study does clearly demonstrate is that dogs with CHF have abnormally low levels of vitamin D in their blood, and those deficiencies decrease their survival times. The researchers concluded, “Strategies to improve vitamin D status in some dogs with CHF may prove beneficial without causing toxicity.”
In Otherwise Healthy Dogs, Too Much Vitamin D is a Greater Risk Than Too Little
Despite evidence that dogs with heart disease may benefit from vitamin D therapy, what every dog owner should keep in mind is that vitamin D toxicity is actually much more common than vitamin D deficiency. Most commercial dog food formulas contain at least the AAFCO minimum recommended amount, as does a balanced homemade diet. (Food sources of vitamin D include halibut and other fish, cod liver oil, cheese, yogurt or kefir, liver, and eggs. These are the vitamin D sources I recommend you provide to your dog instead of a vitamin D supplement.)
Since vitamin D is fat-soluble, your pet’s body absorbs it in the same way dietary fats are absorbed, and excess amounts are stored in the liver. Toxicity most often occurs when a dog gets into either some rodent bait or vitamin D supplements. It can also occur in dogs with well-intentioned owners who feel a daily vitamin D supplement is appropriate for their pet. I do not recommend supplementation with this vitamin, instead opting for a fresh food diet containing abundant food sources of vitamin D. If you can’t feed a fresh food diet, you can opt to use foods rich in vitamin D as treats throughout the day, instead.
Symptoms of toxicity can include excessive drooling, vomiting (sometimes with blood), loss of appetite, increased thirst and urination, weakness, depression, abdominal pain, dark tarry feces, weight loss, constipation, muscle tremors, and seizures.
Vitamin D toxicity is a very serious and potentially life-threatening emergency that requires immediate veterinary intervention. After accidental ingestion of a compound containing vitamin D, the first 72 hours are crucial in saving the dog’s life. Typically, prolonged hospitalization is necessary, and treating a dog with vitamin D poisoning is very costly.
The best way to prevent vitamin D toxicity in your dog is to keep your pet far from any rodent-killing agent, feed a balanced, species-appropriate diet, and never casually offer your pet a vitamin D dietary supplement. Consult with your holistic vet before changing your pet’s diet or starting a new supplement.