Written by Dr. Jill Cline, Ph.D.
Some pet owners are in the habit of adding nutritional supplements to their pet’s commercial diet. However, there are both risks and potential benefits of supplementation. While supplementation may be helpful in certain circumstances with some nutrients, for others the risks clearly outweigh the potential benefits and supplementation should be avoided altogether.
Role of calcium: Calcium is a primary mineral component of bones and teeth and is also found in small amounts throughout the body’s fluids. The calcium in bones supports skeletal strength and health and helps to maintain the strictly regulated levels of calcium that circulates in the bloodstream. Circulating forms of calcium have essential roles in nerve impulse transmission, muscle contraction, and blood coagulation.
Relationship between calcium and phosphorus: Phosphorus, another essential mineral, has an important relationship with dietary calcium. Because an excess of one of these two minerals can interfere with the absorption or use of the other, the ratio of calcium to phosphorus in a dog’s diet is an important consideration. A ratio of approximately 1:1.8 between calcium and phosphorus is recommended for pet foods. Feeding a diet that has an improper calcium/phosphorus ratio or supplementing a balanced food with excessive amounts of either of these minerals can lead to nutrient imbalances.
Beliefs about supplementation: The reason that some pet owners supplement their dog’s diet with calcium relates to its essential role in skeletal growth. Some dog enthusiasts believe that supplementation with calcium during growth is necessary for proper bone development and will help to prevent skeletal diseases such as hip dysplasia and osteochondrosis. In addition some breeders supplement their females’ diets with calcium during gestation and lactation. The added calcium and phosphorus is believed to ensure healthy development of puppies during pregnancy and to aid in milk production during lactation.
Health risks associated with calcium supplementation: Contrary to beliefs, supplementing growing dogs with calcium does not contribute to skeletal health. Rather, adding excess calcium to the diet is associated with abnormal changes to bones that may contribute to the very diseases that owners are attempting to prevent! Because young dogs are unable to efficiently regulate calcium absorption from the intestine, they are highly susceptible to excessive levels in the diet. Any excess calcium that is absorbed is “stored” in the bones, and over time this excess mineral affects cartilage maturation and bone development, leading to abnormally dense bones. Together, these changes can result in serious skeletal disorders.
Tips for healthy calcium nutrition: While it is true that dogs require slightly more calcium during growth, gestation and lactation, these higher requirements are provided through the consumption of a larger volume of food during these nutritionally demanding stages of life. Here are a few feeding tips to ensure that your dog receives optimal calcium nutrition throughout life:
• When feeding a well-balanced, high quality food that is formulated for your dog’s age, breed size and lifestyle, calcium supplementation should not be necessary and is unwarranted.
• Avoid using calcium supplement pills or powders. These provide a highly concentrated source of the mineral and excess levels can be rapidly attained. For example, adding as little as 2 to 3 teaspoons of calcium carbonate each day can increase a dog’s calcium intake to a level that may be harmful. In addition, many commercial calcium supplements do not contain phosphorus and increase the risk of imbalancing the food’s calcium to phosphorus ratio.
• Although they are not as concentrated, adding calcium-rich foods to the diet should also be avoided. Dairy products can contributed excess calcium and may cause gastrointestinal upsets in some dogs.
Vitamin C (Ascorbic Acid) Supplementation
Role of vitamin C: Vitamin C is an essential nutrient that is needed for the formation of collagen, a structural protein found in bone, teeth and connective tissues. Vitamin C also acts as a water-soluble anti-oxidant in the diet and has roles in wound healing and immune health. Although vitamin C is an essential nutrient, dogs do not have an actual dietary requirement for it because they synthesize sufficient quantities of ascorbic acid in the liver. Unless a dog has an unusually high demand for vitamin C, a dietary source of ascorbic acid is not needed (see below).
Beliefs about supplementation: Some owners routinely administer supplemental Vitamin C to their dogs because they believe supplementation will support bone growth and a healthy immune system. Beliefs about the connection between vitamin C nutrition and skeletal development came about as a result of a report published during the 1970’s that suggested vitamin C deficiency as an underlying cause in hypertrophic osteodystrophy (HOD). HOD is a developmental bone disorder characterized by increased density of certain long bones. However, later studies showed that neither HOD nor other developmental bone diseases were related to vitamin C deficiency. Most importantly, there is no evidence that supplementing growing dogs with vitamin C plays a role in preventing skeletal disease. There is some evidence for increased demands for vitamin C during periods of hard work, physiological stress or illness. However, the additional vitamin C found in high quality pet foods should provide for this need.
Health risks associated with vitamin C supplementation: Because ascorbic acid is one of the water-soluble vitamins, it is commonly believed that supplementation will not cause ill effects because excesses are rapidly excreted in the urine. Like many myths, this is partially, but not completely, true. It is true that excess ascorbic acid is excreted in the urine; it is excreted as the break-down product, oxalate. However, increases in urinary oxalate may increase the risk of calcium oxalate uroliths or stones in the urinary tract in dogs who are susceptible. While vitamin C supplementation poses a minimal risk to the majority of dogs, supplementation should be avoided in dogs who are known to be at risk for developing calcium oxalate urinary crystals or bladder stones.
Vitamin E Supplementation
Vitamin E is a fat soluble vitamin that helps to maintain the body’s defenses against cellular damage and disease through its action as an antioxidant. The currently recommended level of vitamin E in dog food is 20 IU per kilogram. This provides optimal vitamin E nutrition for the majority of dogs. However, there is evidence for increased needs for vitamin E in canine athletes during periods of prolonged strenuous exercise. As working muscles rapidly break down (oxidize) nutrients for energy, they also rapidly utilize vitamin E. Providing a food with increased vitamin E or adding a dietary supplement can help to minimize the oxidative tissue damage associated with endurance exercise and prevent vitamin E depletion in hard working dogs. Most high quality commercial foods that are formulated for performance include additional vitamin E to meet the needs of canine athletes. Alternatively, if supplementation is used, the form of vitamin E is important. Products containing alpha-tocopherol, alpha-tocopherol acetate, or alpha-tocopherol succinate are the most effective forms of vitamin E and should be selected.
Potential health risks associated with Vitamin E supplementation: Because vitamin E is absorbed into the body by the same route as the other fat soluble vitamins (A, D and K), excessive supplementation may interfere with the absorption of these nutrients. For example, there is evidence that excessively high levels of vitamin E intake can contribute to bleeding disorders that are associated with vitamin K deficiency. The source of vitamin E should also be considered. Some supplements contain other fat-soluble vitamins, such as Vitamin A. Feeding this type of supplement to dogs on a long term basis could lead to vitamin A toxicity and should be avoided.
Omega-3 Fatty Acid Supplementation
Although the omega-3 fatty acids are not classified as essential nutrients, they have important immune and anti-inflammatory functions that contribute to a dog’s health and vitality. Research studies have shown that increasing the amount of omega-3 fatty acids in the diet modulates the immune response and is helpful in managing certain types of inflammatory disorders. One particular omega-3 fatty acid, Docosahexaenoic acid (DHA), is also important for development of the nervous system and vision. Increasing omega-3 fatty acid intake is usually accomplished by feeding a therapeutic diet containing higher levels of these nutrients or adding an omega-3 fatty acid supplement to the dog’s normal maintenance diet.
Potential health risks associated with omega-3 fatty acid supplementation: Although the omega-3 fatty acids have a very wide safety margin, providing too high a concentration should be avoided. An excessively high intake may contribute to alterations in immune function, modified blood clotting response, and increased susceptibility to disease. If your dog has been diagnosed with an inflammatory disease that may respond to omega-3 fatty acid supplementation, follow your veterinarian’s recommendations regarding the use of an appropriate therapeutic diet or providing a safe level of supplementation.
A Few Cautionary Tips
• Nutritional supplements should never be used in place of a nutri¬tionally complete and balanced diet. Attempting to improve a poor quality dog food through supplementation can cause nutrient deficiencies and imbalances.
• Although supplements may be beneficial in certain situations, they should never replace veterinary care and a complete diagnosis for suspected disease states. If your dog shows signs of illness, seek veterinary care.
• Just as with human foods and supplements, it is important to read labels! If you are using a supplement, select a product that contains the nutrient in highly available forms and does not include unnecessary (or unwanted) nutrients. Avoid “economical” brands as these often contain nutrients that are less available or may be contaminated with other components.