Cat calcium supplements are great, if your cat needs them. But, if she doesn't the extra calcium may be harmful to her health. Here's how to decipher your cat's needs.
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There are a variety of calcium supplements for cats on the market, but how do you know if your cat needs one? For answers, we spoke to veterinarians about the telltale signs your cat could use a calcium boost, what to look for in a supplement for your cat, how much calcium cats need, and more.

How Much Calcium Does a Cat Need?

Calcium is an essential mineral for cats and is important for the formation of bones and teeth. Calcium also helps blood clot, aids in nerve impulse transmission, and supports muscle contractions.

Ask your vet for your cat's specific calcium needs, however, the National Research Council of National Academies recommends 180 milligrams of calcium daily for the average mature cat weighing about 9 pounds (and requiring 250 calories per day).

The National Animal Supplement Council (NASC) explains that adult cats need 0.6 percent of their total diet to be calcium, but calcium also needs to be balanced with phosphorus. Ideally, cats should be getting 1.2 parts calcium for every 1 part of phosphorus. A veterinarian can help make sure your cat gets the right amount of both nutrients.

Pregnant and nursing cats need extra calcium and phosphorus to help their developing kittens grow healthy bones, and for producing milk once their kittens are born.

Do I Need to Add More Calcium to My Cat's Diet?

In the U.S., cats are fed complete, balanced food that contains enough calcium to meet their dietary needs. So, before giving your cat extra calcium be sure to check with your vet. "Adding calcium to such a diet might lead to excess and issues like kidney or bladder stones (aka calcium oxalate uroliths)," says Sean J. Delaney, BS, DVM, MS, DACVIM (Nutrition) founder of Balance It and Board Certified Veterinary Nutritionist®.

However, Delaney explains that cats who receive more than 10 percent of their daily calories from incomplete and unbalanced foods do need calcium supplements. This may include cats eating a homemade diet that isn't nutritionally balanced or cats who aren't eating enough of their regular cat food when it's feeding time (which can be a sign of a medical issue and should be addressed with your vet right away). Cats with hypoparathyroidism, a metabolic illness characterized by low calcium and high phosphate, might also need a cat calcium supplement, according to Jonathan Roberts, BVSC, a remote veterinarian at petkeen.com. "The most common cause of low calcium levels in cats is chronic kidney failure," he adds. However, giving a cat with kidney disease calcium "has recently been questioned as preliminary data suggests that a higher calcium to phosphorus ratio could theoretically lead to more rapid renal disease progression," says Delaney. Bottom line: talk to your vet before giving your cat any type of supplement, including a cat calcium supplement.

Another condition that may require calcium supplements is milk fever (also known as puerperal tetany and eclampsia), a life-threatening illness that's caused by a sudden drop in blood calcium levels in lactating cats. "This usually starts within the first few days or weeks of nursing and if not treated immediately can lead to death," Roberts says. Signs of eclampsia in cats are subtle, but include panting, restlessness, fever, muscle stiffness, and muscle spasms. If your cat shows any of these symptoms, take her to the vet immediately, as it is a medical emergency.

Michelle Burch, a DVM from Paramount Pet Health, says that she only recommends calcium supplementation in cats "if there is a diagnosis causing low calcium blood levels or a cat is not eating a well-balanced diet causing low calcium levels." Your vet can draw your cat's blood to determine if his calcium is low, she adds.

Signs of Low Calcium in Cats

Moderate or severe low blood calcium levels in cats can be life threatening. Early signs of low blood calcium in cats include:

  • Muscle tremors
  • Restlessness
  • Stiffness
  • Weakness
  • Irritability
  • Hypersensitivity
  • Muscle twitching
  • Involuntary contractions of muscles and/or convulsions
  • In severe cases, death can also occur

What Happens If a Cat Has High Calcium Levels?

To tell if your cat has high blood calcium, your veterinarian will conduct routine bloodwork. Signs of high calcium in the blood include:

Some symptoms of high calcium may be associated with a medical condition. For example, difficulty urinating or blood in the urine may be due to calcium-containing crystals or stones in the bladder.

Before adding any supplement to your cat's diet, always check in with your veterinarian to make sure it will benefit (not harm) your kitty's overall health.