In humans, epidemiological data have associated low vitamin D status with many diseases, including a variety of cancers. Moreover, it has been shown in humans that low vitamin D status is linked with poor prognosis in cancer patients. Until recently, there has been little interest in applying this information to dogs- even though cancer has become more common as dogs live longer that in previous years. Estimates are that 40-50% of pet dogs die of cancer. We now have an epidemic of cancer in dogs- and very little is being done to reduce the cancer death rate in dogs. A beginning would be to apply the knowledge we have about cancer in humans to dogs.
In humans, only 5-10% of all cancers can be attributed to genetic defects, whereas the remaining 90-95% have their roots in the environment and lifestyle. It seems reasonable to assume that the same is true of dogs. Again in humans, many factors have been associated with cancer- smoking, poor diet, excessive alcohol consumption, and lack of exercise are well known. There are many other factors that are less well known. Vitamin D status is one of them.
A review of the literature by VDI Labs found recent studies associating low vitamin D status with disease in the dog. Three of these studies demonstrated that low vitamin D status is associated with increased risk for cancer of various types. The other studies found the same association of low vitamin D with diseases such as renal failure, congestive heart failure, and inflammatory bowel disease.
One of the studies found that the risk of cancer increased as the level of vitamin D decreased. The protective level of vitamin D was found to be a serum level greater than 100 ng/ml. Another study of 320 apparently healthy dogs on 41 different manufacturers of commercial dog food showed that serum vitamin d levels ranged from 9.5 to 249 ng/ml. It is necessary to test individual dogs to find their vitamin D levels as too little is not protective and too much is toxic. Serum vitamin D testing is done by an inexpensive blood test. Given the importance of Vitamin D as a preventive health care measure, we recommend it for all dogs.