Calcium, Phosphorus and Vitamin D

Why are calcium, phosphorus and vitamin D important for growing dogs?

Calcium, phosphorus and vitamin D have key roles in skeletal development and health as well as other metabolic functions. They are essential nutrients required as part of a complete and healthy diet. Healthy bones protect a dog’s brain, heart, lungs and other important organs. Bones also anchor muscles and store minerals. Your dog’s bone health depends on a balanced diet and quality nutrition.

Most commercial diets provide sufficient amounts of calcium, phosphorus and vitamin D, but homemade diets may be deficient or unbalanced in these nutrients. Calcium and phosphorus need to be provided in the diet in adequate amounts and bioavailable forms. Your growing puppy is not going to absorb enough calcium and phosphorus from eating raw chicken bones.

Calcium and phosphorus are the first and second most abundant minerals in the body. They are important in bone and tooth formation, as well as functional roles. Calcium is involved in blood clotting and nerve transmission. Phosphorus has a major role in energy metabolism. Dogs need vitamin D to absorb and retain calcium and phosphorus from their food.

Calcium is not made in the body, so it must be absorbed from food. If a dog’s diet is deficient in calcium, its body will use calcium from its bones for other purposes. This can lead to weakened, fragile and brittle bones. Calcium deficiency can also lead to nervous-system problems.

On the other hand, overloading a dog with calcium can also cause problems. Feeding high levels of calcium to puppies can promote excessively rapid bone growth, which can lead to decreased skeletal health as an adult.

There needs to be a proper balance between calcium and phosphorus for ideal bone growth and health. It is not a good idea to supplement calcium without knowing the dog’s actual calcium levels. Good-quality commercially prepared foods have the correct amount of calcium and other minerals, so additional supplements are not required.

Phosphorus works with calcium to build bones. The majority of phosphorus, up to 80 percent, is found in bone mineral. Phosphorus aids in calcium metabolism. It also aids in the repair of bones at the cellular level. The outer lining of bones contains protein that dogs also get from their diet. Phosphorus helps repair any damage to the outer lining of bones.

A deficiency of phosphorus can lead to weakened bones and pain.

Vitamin D is an essential vitamin and is required for a dog to absorb the calcium from his food. Dogs cannot produce enough vitamin D on their own. It must be included in their diet or by exposure to sunlight to maintain optimal health. Vitamin D plays an indirect role in the health of bones by managing the levels of calcium in the body. It also controls the absorption and movement of calcium throughout the body.

Like other nutrients, vitamin D must be appropriately balanced. Vitamin D is a fat-soluble vitamin, and excess amounts are stored in the liver instead of being excreted. Excess vitamin D in the liver can be toxic for dogs, so it is best to feed a high-quality dog food that has a balanced blend of vitamins and minerals.

Magnesium is another mineral that is important for healthy bones. Magnesium promotes muscle and nerve function, as well as supporting central nervous system and cardiovascular health. A lack of magnesium in a dog’s diet can lead to weakened bones, nervous system diseases, a lowered level of stamina, and an unresponsive immune system. Magnesium also plays a part in hundreds of biochemical reactions in the body.

What disorders are associated with calcium, phosphorus and vitamin D in dogs?

Defective bone formation is called osteodystrophy. In most cases it is caused by deficiencies or imbalances of calcium, phosphorus, vitamin D and the hormone that regulates them — parathyroid hormone. Supplementing a dog’s diet with too much calcium or phosphorus can increase the susceptibility to disease to which the dogs are genetically prone. Giant-breed dogs that are fed excess calcium are more likely to develop osteochondrosis and hypertrophic osteodystrophy (HOD).

Rickets is a rare disease of young, growing dogs that causes soft and deformed bones. It is commonly caused by insufficient phosphorus or vitamin D in the diet. More rarely, calcium deficiency is to blame. When dogs are fed too much calcium in their diet, they may develop rickets-like symptoms. The cause is typically an imbalance in the ratio of calcium to phosphorus in the diet. Dogs fed all-meat diets commonly develop rickets.

Signs may include bone pain and swelling, a stiff gait or limp, difficulty in standing up, bowed limbs and fractures. Affected puppies may become quiet and reluctant to play. Touching the bones will cause pain, and folding fractures of the long bones and vertebrae are common.

In folding fractures, pressure on the bones causes them to slowly “fold” over and deform instead of fracturing. X-rays will show distortions in the bone. In advanced cases, limbs can be deformed due to the bones growing at uneven rates.

The prognosis for treating rickets is good if there are no broken bones or irreversible damage to the bones. The primary treatment is to correct the diet. Exposure to sunlight (ultraviolet radiation) will also increase the production of vitamin D.

Adult rickets, also known as osteomalacia, develops similarly to rickets but in mature bones. Because bones mature at different rates, both rickets and osteomalacia can be seen in the same dog.

Affected dogs may be sickly, and crave and eat substances such as paint chips, clay, plaster or dirt. Bone fractures are most commonly found in the ribs, pelvis and long bones. Long bones are the main bones of the front and rear legs, which are the femur, tibia, fibula, humerus, radius and ulna. Deformities may also be seen in the spine, including an abnormal inward curving of the spine in the lower area of the back called lordosis or an abnormal outward curving of the spine called kyphosis.

To establish a firm diagnosis, a veterinarian will evaluate the dog’s diet to ensure it provides enough calcium, phosphorus and vitamin D for healthy bones. The severe effects of osteomalacia on the skeleton can be seen on X-rays. The response to proper nutrition is rapid. Within a week, the dogs become more active and can usually resume normal activities after three weeks.

Primary hyperparathyroidism is a condition where the parathyroid gland produces too much parathyroid hormone. This hormone controls the metabolism of calcium and phosphorus in the body. This is a rare disease that usually occurs in older dogs.

When too much parathyroid is released over a long period of time, minerals are leached from the skeleton and replaced by immature fibrous connective tissue. This is called fibrous osteodystrophy, or “rubber jaw syndrome.” It affects the entire skeleton, but tends to concentrate in the bones of the skull.

Dogs with primary hyperparathyroidism may become lame and develop fractures of the long bones after minor physical trauma. Compression fractures in the spine place pressure on the spinal cord, which may lead to difficulty standing and walking.

In some cases, the condition causes thickening of facial bones. Nasal cavities may be damaged and teeth loosened. Some dogs lose the ability to close their mouth properly and develop slow-healing sores on their gums. Often the jaw bones become thickened while the bones in the skull grow thin and appear “moth-eaten” on X-rays. The name “rubber jaw” syndrome refers to advanced cases in which the jaw can be twisted gently due to the deterioration of the bone.

Blood tests on dogs with primary hyperparathyroidism will show an abnormally high level of calcium. Tests can also be performed to determine phosphorus and parathyroid hormone levels to confirm the diagnosis.

The goal of treatment is to eliminate the source of excessive parathyroid hormone production. If a tumor is the cause, it must be removed. However, removing the source of increased hormone production may cause calcium levels to drop suddenly to dangerously low levels. The calcium levels need to be monitored and corrected. If high levels of calcium persist a week or longer after surgery or recur after initial improvement, a second tumor or the spread of cancer from a malignant tumor may be causing the problem.