Reducing high calcium levels in cats typically starts with a dietary change, and in many cases, that alone is enough. A recent study in the Journal of Feline Medicine and Surgery found that 60% of cats with elevated calcium returned to normal levels after switching to a diet with less than 200 mg of calcium per 100 kilocalories and a calcium-to-phosphorus ratio below 1.4:1. For cats that don’t fully respond to diet, medications and other strategies can bring levels down further.
Before jumping into treatment, though, it’s important to understand why your cat’s calcium is high. The cause shapes everything about how it’s managed.
Why Your Cat’s Calcium May Be High
The most common reason cats develop elevated calcium is idiopathic hypercalcemia, meaning no underlying disease can be identified. This is a diagnosis of exclusion: your vet rules out other causes first.
Cancer accounts for up to 30% of hypercalcemia cases in cats. Lymphoma and squamous cell carcinoma are the most frequent culprits, though multiple myeloma, osteosarcoma, and other tumors can also raise calcium. In these cases, treating the cancer itself is the primary way to bring calcium down. Other causes include overactive parathyroid glands, chronic kidney disease, and certain infections. Each requires its own targeted approach, so getting a clear diagnosis matters before focusing on calcium reduction strategies.
Signs to Watch For at Home
High calcium in cats often produces vague symptoms that are easy to miss or attribute to aging. The most commonly reported signs are decreased appetite and lethargy. As levels climb higher, you may notice increased thirst and urination, vomiting, or weight loss.
One significant complication is the formation of calcium oxalate stones in the urinary tract. About 35% of cats with idiopathic hypercalcemia develop these stones, and conversely, 35% of cats found to have calcium oxalate stones turn out to be hypercalcemic. If your cat is straining to urinate or producing small, frequent amounts of urine, that’s worth flagging to your vet promptly.
Dietary Changes: The First-Line Approach
For cats with idiopathic hypercalcemia or kidney disease-related calcium elevation, switching to an appropriate diet is the most important step you can take. The target is a food providing less than 200 mg of calcium per 100 kilocalories, with a calcium-to-phosphorus ratio below 1.4:1. In the study that tested this approach, the diets cats actually ate had a median calcium content of 166 mg per 100 kilocalories and a median calcium-to-phosphorus ratio of 1.1:1.
This matters because not all therapeutic diets are created equal. Some low-phosphorus renal diets that are commonly recommended for kidney disease can actually worsen hypercalcemia. One such diet providing 80 mg of phosphorus per 100 kilocalories had a calcium-to-phosphorus ratio of 1.8:1, well above the threshold. The low phosphorus content sounds helpful for kidneys, but the relative excess of calcium can push blood calcium higher. If your cat has kidney disease and develops high calcium on a renal diet, ask your vet about switching to one with a calcium-to-phosphorus ratio under 1.4:1.
Increasing dietary fiber is another strategy that may help. Fiber appears to reduce how much calcium the intestines absorb. Several proposed approaches exist for managing feline hypercalcemia through diet, including low-calcium diets, high-fiber diets, renal diets, and urinary diets. Your vet can help identify specific commercial foods that meet the right nutritional profile for your cat’s situation.
Chia Seeds as a Supplement
For cats that only partially respond to a diet change, adding 1 to 2 grams of chia seeds per day has shown promise. In the same study, two cats that hadn’t fully normalized on diet alone achieved normal calcium levels after chia seeds were added. The mechanism likely relates to chia’s high fiber and phytate content, which can bind calcium in the gut and reduce absorption. One to two grams is a small amount, roughly a quarter to half a teaspoon, and can be mixed into wet food.
Medications That Lower Calcium
When dietary management isn’t enough, or when calcium levels are dangerously high, medications become part of the plan.
Alendronate is the most commonly used medication for persistent feline hypercalcemia. It belongs to a class of drugs called bisphosphonates that slow the breakdown of bone, which is one of the main sources of calcium entering the bloodstream. The typical starting protocol is 10 mg given by mouth once per week. If calcium doesn’t drop sufficiently, the dose can be increased to 15 mg weekly (usually around six weeks in), and further to 20 mg weekly if needed. One important detail: cats need to be fasted for 12 hours before and 6 hours after each dose, and the pill should be given with water or a small amount of butter to prevent it from getting stuck in the esophagus, which can cause irritation.
Glucocorticoids like prednisolone can also reduce calcium by increasing how much the kidneys excrete and decreasing how much the gut absorbs. These are particularly useful when hypercalcemia is caused by lymphoma or other cancers that respond to steroids. However, steroids come with their own side effects over time, so they’re not always the first choice for long-term management of idiopathic cases.
Fluid Therapy for Acute Cases
If your cat’s calcium is critically high and causing serious symptoms, your vet will likely start with intravenous fluids. Normal saline promotes calcium excretion through the kidneys. This is a hospital-based treatment, not something done at home, and it works quickly to bring levels into a safer range while the underlying cause is investigated. Think of it as a bridge to stabilize your cat while longer-term solutions are put in place.
Treating the Underlying Cause
Reducing calcium is important, but it’s equally important to address whatever is driving it up. If a parathyroid tumor is overproducing hormones, surgical removal of the affected gland can be curative. If cancer is the cause, treatment directed at the tumor (surgery, chemotherapy, or radiation depending on the type) is the most effective way to normalize calcium. For kidney disease, managing the kidney condition itself with appropriate diet and supportive care helps keep calcium in check.
For the large number of cats with idiopathic hypercalcemia, where no cause is found, dietary management with or without alendronate is the mainstay. These cats often do well long-term, but they need regular monitoring. Your vet will recheck calcium levels periodically to make sure the chosen strategy is working and to catch any changes early, especially the development of urinary stones.
Putting It All Together
The practical sequence for most cat owners looks like this: get a diagnosis to rule out cancer, kidney disease, and parathyroid problems. If the hypercalcemia is idiopathic or related to kidney disease, start with a diet providing less than 200 mg calcium per 100 kilocalories and a calcium-to-phosphorus ratio under 1.4:1. Recheck calcium levels in a few weeks. If levels haven’t normalized, try adding 1 to 2 grams of chia seeds daily. If that’s still insufficient, alendronate given weekly is the next step. Throughout this process, watch for increased thirst, changes in urination, appetite loss, or lethargy, and keep up with the rechecks your vet recommends.