Saturday, November 3, 2012

Nutritional Management of Idiopathic Hypercalcemia in Cats

Over the last 15 years, idiopathic hypercalcemia has emerged to become the most common cause of hypercalcemia in cats (1-8). Although the underlying cause of this syndrome remains unclear, it is very likely that the cats' diet may be involved, especially the feeding of acidifying, magnesium-restricted diets designed to minimize struvite crystalluria and urolithiasis (9,10). For more information, see my last post on What's Causing Idiopathic Hypercalcemia in Cats?

Before the introduction of high-carbohydrate, magnesium-restricted acidifying diets by the pet food industry, cats did not develop idiopathic hypercalcemia — at least it was never reported until 1999, (1) and I certainly did not see a cat until the mid-1990s.

Nutritional Therapy

I generally start with diet modification as a first-line treatment. If an acidifying diet is being fed, it should be discontinued. However, it may not always be clear that the cat food being fed is an acidifying diet — one should always closely examine the ingredient list to look for the presence of an added urinary acidifier, such as dl-methionine, phosphoric acid, and ammonium chloride.

Although feline urine is normally mildly acidic, feeding cats commercial diets containing high amounts of carbohydrate (e.g., starch and fiber) will result in an alkaline urine pH (11,12). Therefore, many commercial cat food diets contain added acidifiers in order to “counteract” the alkalizing effects of the high carbohydrate diet, even when it is not promoted as a urinary tract diet.

No matter what type of diet is chosen, it is best to feed a wet-only diet to promote urinary dilution and lessen the chance for calcium oxalate stones (13). To this end, we have a variety of different types of cat food diets that have been proposed to help lower calcium in cats with idiopathic hypercalcemia (3-8).

Diets Recommended in the Literature

High-fiber diets
High fiber diets (e.g., Purina OM Overweight Management, Iams Intestinal Plus Low-Residue, Hill’s w/d) will restore normocalcemia in some cats with idiopathic hypercalcemia and calcium oxalate urolithiasis (1,5). The effects of fiber on intestinal absorption are complex and depend on the type and amount of fiber, as well as the interactions with other nutrients in the diet. However, these “high fiber diets” are usually supplemented with extra calcium; therefore, calcium content does not explain why these diets are occasionally helpful in treating idiopathic hypercalcemia. Again, changing from an acidifying diet to any diet that is less acidifying (such as high fiber) would be expected to be beneficial.

Another option, of course, would be to feed a lower calcium diet and add fiber to the diet (e.g., psyllium for a mixed-fiber source or guar gum for an all-soluble source) (8). However, because high-fiber diets tend to be lower in protein, cats with idiopathic hypercalcemia chronically fed these diets can loose lean muscle mass to become muscle wasted (14,15). This is especially true if the cat’s appetite is poor, a sign present in some cats with this syndrome (1-8).

Overall, I do not find high-fiber diets to be helpful in the vast majority of cats with idiopathic hypercalcemia and no longer recommend these diets.

Renal diets
Prescription kidney diets (e.g., Purina NF Kidney Function, Royal Canin Renal LP Modified, Iams Renal Plus, Hill’s k/d) also may result in normocalcemia in some cats with idiopathic hypercalcemia (5,6). Although these renal diets appear less acidifying than most maintenance or high-fiber diets, many renal diets still contain added dl-methionine. Most renal diets are low in calcium, so its decreased consumption should lead to a decrease in the amount of calcium absorbed (4).

Remember, however, that renal diets are also restricted in phosphorus, which may lead to increased calcitriol (active vitamin D) synthesis by the kidney; the action of this increased serum calcitriol could offset the advantage of the decreased calcium absorption in cats with idiopathic hypercalcemia (5,16).

Overall, because these diets are lower in protein, renal diets are not my first choice — with time, cats with idiopathic hypercalcemia can become muscle wasted on these diets (14,15).

Diets for calcium oxalate urolithiasis
Canned diets developed to prevent calcium oxalate urolithiasis (e.g., Royal Canin Urinary SO, Purina UR Urinary St/Ox, Iams Urinary-O Plus Moderate pH/O, Hill’s c/d) may be beneficial in the treatment of cats with idiopathic hypercalcemia (5,6). These diets are restricted in calcium and tend to be less acidifying, resulting in a neutral urine pH in most cats. However, some still contain dl-methionine, which should definitely be avoided. Some of these diets are also restricted in oxalic acid, which may help prevent the calcium oxalate stones that develop in 10-15% of cats with idiopathic hypercalcemia.

However, I do not find any of these “calcium oxalate” diets to be very helpful in normalizing the high ionized calcium concentrations found in cats with idiopathic hypercalcemia. Therefore, I cannot strongly recommend these diets, especially if no calcium oxalate stones are present.

Diets That I Recommend

Canned commercial diets with a "natural" macronutrient composition
Feeding commercial canned diets with a composition similar to what cats would eat in the wild—i.e., 40-60% protein, 30-50% fat, and <15% carbohydrates (17-20)— will also be beneficial in lowering serum calcium concentrations in some cats, particularly those with mild forms of idiopathic hypercalcemia.

One can use the online “Protein/Fat/Carbs Chart” found at to select a canned cat food that will provide a nutritional composition similar to what cats would ingest in small prey (e.g., small rodents, birds, and insects). Although this diet composition will result in an acidic urine pH (normal for cats), a high-protein diet is preferable over added acidifiers for prevention of struvite crystal formation in cats (12,21) and is not associated with the same degree of metabolic acidosis.

In addition to the macronutrient composition, one should ensure that the canned food selected does not have any added acidifiers (e.g., dl-methionine, phosphoric acid, or ammonium chloride) and is not a magnesium-restricted diet. A diet with a relatively low vitamin D content (< 5 μg [< 200 IU]/1000 kcal) is recommended. Although feeding a low-calcium diet may be ideal, none of the available commercial cat foods are calcium-restricted.

Home-prepared diet restricted in both calcium and vitamin D
For more control over the exact macronutrient, mineral, and vitamin D content of the cats’ diet, feeding a specially formulated, home-prepared diet is recommended. Some cats, especially those with mild ionized hypercalcemia, will show a good response to a diet restricted in both calcium and Vitamin D (22). Such diets must be specially formulated, since none of the commercial cat food diets could be low in either calcium or vitamin D content and still meet AAFCO guidelines to be a “complete and balanced” diet (23).

Again, I recommend formulating this diet to have a macronutritional composition similar to what cats would eat in the wild (i.e., 40-60% protein, 30-50% fat, and < 10% carbohydrates). Products containing high concentrations of vitamin D, such as organ meats and fish oil, should be avoided (22). Calcium content should be kept restricted to 600 mg per 1000 kcal of diet (in contrast, the minimal adult maintenance requirement set by AAFCO is 1500 mg per 1000 kcal) (23). Magnesium should not be restricted, and acidifiers should never be added.

Ideally, this home-prepared diet is formulated under the guidance of a veterinary nutritionist to ensure that it is nutritionally adequate for the cat. If no response is detected after a month or two on this restricted calcium diet, alternative medical therapies (e.g., glucocorticoids, alendronate) should be considered.

My Bottom Line

In cats with idiopathic hypercalcemia, clinical signs and the associated degree of ionized hypercalcemia are usually mild, at least at diagnosis. In general, the severity of hypercalcemia in these cats tends to be slowly progressive.

Therefore, as the first step in management of these cats, I recommend changing their diet to a canned food that has a macronutrient composition closer to a cat’s carnivorous diet in the wild — in other words, high protein, moderate fat, very low carbs, not magnesium-restricted, and no added acidifiers (17-20). Remember that, at least as far as we know, cats eating this way for many hundreds of years did not develop idiopathic hypercalcemia, so I'm hoping that Mother Nature knows best when it comes down to what these cats should be fed.

One should monitor ionized calcium concentrations at 4 and 8 weeks during this initial dietary change. If hypercalcemia persists, the diet can be switched to a home-prepared, formulated calcium- and vitamin D-restricted diet (22). Again, I would still maintain a macronutrient composition that mimics a cat’s natural diet.

If nutritional management fails to normalized ionized calcium concentrations or hypercalcemia is severe, drug therapy with glucocorticoids (e.g., daily oral prednisolone) or bisphosphonates (e.g., weekly oral alendronate) can be initiated (5-8,24). However, both of these drugs can produce adverse side effects (i.e., diabetes mellitus and esophagitis, respectively), so I prefer to withhold drug therapy until absolutely needed (8,25).

Once drug therapy has been instituted, I would still maintain the feeding a low-carb, high-protein canned diet to these cats. The higher protein intake will help maintain lean body mass, whereas the lower carbohydrates may help mitigate the diabetic effects of the high doses of prednisolone that may be needed to control hypercalcemia.

But in some cats, we'll be lucky, and the hypercalcemia will resolve after a change in the cat's diet to one with a nutrient composition closer to the food they were designed to eat. And in a few of those cats, the ionized calcium concentrations will remain normal for months to years, without the need for drug therapy.

  1. McClain HM, Barsanti JA, Bartges JW. Hypercalcemia and calcium oxalate urolithiasis in cats: a report of five cases. J Am Anim Hosp Assoc 1999;35:297-301.
  2. Midkiff AM, Chew DJ, Randolph JF, et al. Idiopathic hypercalcemia in cats. J Vet Intern Med 2000;14: 619–626.
  3. Savary KC, Price GS, Vaden S. Hypercalcemia in cats: a retrospective study of 71 cases (1991-1997). J Vet Intern Med 2000; 14:184-189.
  4. Schenck PA and Chew DJ: Idiopathic hypercalcemia in cats. Waltham Focus 2005; 15: 20-24.
  5. Chew DJ, Schenck PA. Idiopathic feline hypercalcemia In: Bonagura JD,Twedt DC, eds. Kirk's Current Veterinary Therapy XIV. Philadelphia: Saunders Elsivier, 2009; 236-241.
  6. de Brito Galvao JF, Schenck PA, Chew DJ. Hypercalcemia: Diagnosis and treatment options in dogs and cats. Veterinary Focus 2011;21:27-34.
  7. Schenck PA, Chew DJ. Investigation of hypercalcaemia and hypocalcaemia. In: Mooney CT, Peterson ME, eds. BSAVA Manual of Canine and Feline Endocrinology, Fourth ed. Quedgeley, Gloucester: British Small Animal Veterinary Association. 2012: 221-233.
  8. Baral RM. Disorders of calcium metabolism In: Little SE, ed. The Cat: Clinical Medicine and Management. St. Louis: Elsevier Saunders, 2012; 625-642.
  9. Ching SV, Fettman MJ, Hamar DW, et al. The effect of chronic dietary acidification using ammonium chloride on acid-base and mineral metabolism in the adult cat. J Nutr 1989;119: 902-915.
  10. Fettman MJ, Coble JM, Hamar DW, et al. Effect of dietary phosphoric acid supplementation on acid-base balance and mineral and bone metabolism in adult cats. Am J Vet Res 1992;53:2125-2135.
  11. Funaba M, Uchiyama A, Takahashi K, et al. Evaluation of effects of dietary carbohydrate on formation of struvite crystals in urine and macromineral balance in clinically normal cats. Am J Vet Res 2004;65:138-142.
  12. Funaba M, Yamate T, Hashida Y, et al. Effects of a high-protein diet versus dietary supplementation with ammonium chloride on struvite crystal formation in urine of clinically normal cats. Am J Vet Res 2003;64:1059-1064.
  13. Buckley CM, Hawthorne A, Colyer A, et al. Effect of dietary water intake on urinary output, specific gravity and relative supersaturation for calcium oxalate and struvite in the cat. Brit J Nutr 2011;106 Suppl 1:S128-130.
  14. Wolfe RR. Sarcopenia of aging: Implications of the age-related loss of lean body mass. Proceedings of the Nestlé Purina Companion Animal Nutrition Summit: Focus on Gerontology. St. Louis, MO. 2010, pp. 12-17.
  15. Little SE. Evaluation of the senior cat with weight loss In: Little SE, ed. The Cat: Clinical Medicine and Management. St. Louis: Elsevier Saunders, 2012;1176-1181.
  16. Chew DJ, DiBartola SP, Schenck PA. In: Canine and Feline Nephrology and Urology. Second Ed. St. Louis: Elsevier Saunders, 2011.
  17. MacDonald ML, Rogers QR, Morris JG. Nutrition of the domestic cat, a mammalian carnivore. Annu Rev Nutr 1984;4:521-562.
  18. Zoran DL. The carnivore connection to nutrition in cats. J Am Vet Med Assoc 2002;221:1559-1567.
  19. Zoran DL. The unique nutritional needs of the cat In: Ettinger SJ, Feldman EC, eds. Textbook of Veterinary Internal Medicine. 7th ed: Saunders Elsevier, 2010;652-659.
  20. Eisert R. Hypercarnivory and the brain: protein requirements of cats reconsidered. J Comp Physiol B 2011;181:1-17.
  21. Funaba M, Hashimoto M, Yamanaka C, et al. Effects of a high-protein diet on mineral metabolism and struvite activity product in clinically normal cats. Am J Vet Res 1996;57:1726-1732.
  22. Fascetti AJ, Delaney SJ. Nutritional management of endocrine disease. In: Fascetti AJ, Delaney SJ, eds. Applied Veterinary Clinical Nutrition. West Sussex: Wiley-Blackwell; 2012:289-300.
  23. AAFCO (Association of American Feed Control Officials). Official Publication, 2012.
  24. Whitney JL, Barrs VR, Wilkinson MR, et al. Use of bisphosphonates to treat severe idiopathic hypercalcaemia in a young Ragdoll cat. J Fel Med Surg 2011;13:129-134.
  25. Lowe AD, Graves TK, Campbell KL, et al. Apilot study comparing the diabetogenic effects of dexamethasone andprednisolone in cats. J Am Anim Hosp Assoc 2009;45:215-224.


Unknown said...


What if your cat with hypercalcemia already has kidney failure? My cat had acute renal failure in January and one of his kidneys is 75% of normal size and will be on fluids on Chinese herbs indefinitely. He's also on a renal diet that is low in protein. Would you still recommend a high protein diet for a cat in this situation? Thank you.

Dr. Mark E. Peterson said...

Depends on the severity of renal disease. Has ionized hypercalcemia been documented and other causes for hypercalcemia (malignancy, primary hyperparathyroidism) been excluded? Talk to your vet.

Carla said...

Hi Dr. Peterson,

My 7 y.o. male has IHC. I am considering switching him to a raw only diet of Dr. Lisa Peterson. I got your posts from website and a test case cat, Mouse, calcium has returned to normal on this diet. It does have chicken liver and heart in it. Here is the recipe:

4.5 pounds (2 kg) chicken thighs including bones and skin
14 oz (400 g) chicken hearts [if not using – add 14 oz (400 g) meat/bones to recipe and add 4000 mg taurine]
7 oz (200 g) chicken livers
2 cups (475 mL) water
4 egg yolks (raw egg whites contain avidin which depletes biotin)
4000 mg wild salmon oil (never cod liver oil)
200 mg vitamin B complex
800 IU vitamin E
1.5 teaspoons (9 g) lite iodized salt
4000 mg taurine additionally, if freezing for more than a week.

Do you think that this would be beneficial to feed him?

Also, he has been on grain free and dry food for a long time and I am weaning him off the dry (Nature's Variety, raw coated.

Thank you so much.


Dr. Mark E. Peterson said...

I would recommend that you consult directly with Dr. Lisa Pierson about the diet. She will be very helpful... good luck!

Unknown said...

Hello Dr Peterson

Our 3 year old Siberian cat is undergoing investigation for hypercalcemia and myself and the vet is starting to suspect IHC (x ray, ultrasound and so forth all turned out ok).

We are currently trying to find an suitable catfood brand/type but we are having trouble finding one that i appropriate.

Therefore I have a couple of questions that I hope you could help me with:
1. Is it possible/recommendable to find a diet that is totally methionin free (since dl-methionin is an essential amino acid) or should the diet just not contain excessive levels of methionin (as a means of acidifing the diet)? We are currently using royal canin intense beauty gravy which does contain some dl-methionin, but only to reach appropriate levels of this amino acid (according to royal canin)
2. Where we live there is an commercial available raw food based on chicken or chicken/beefliver/salmon. This does however contain roughly 6 000 mg calcium/1000 kcal which is a lot higher then the levels you recommend (at the moment I have no information about vitamin D levels). But do you still think this is a better alternative then royal canin which contains grain products and some methionin but only about 2 000 mg calcium/1000 kcal and about vitanmin D3 150 IU/1000 kcal?
3. Can you recommend any brands of canned commercial diets with a "natural" macronutrient composition, preferably that might be available in europe/sweden?
4. Do you know of any raw food recipe that meats all of you criteria?

And thank you for an excellent blog.

Kind Regards
Henrik Andersson, MD

Dr. Mark E. Peterson said...

We don't know what causes this problem, and dl-methionine may not be the problem. Many foods contain low amounts of dl-methionine and that should be fine.

I don't know what commercial foods you have.. if you are willing, I'd have a veterinary nutritionist formulate a diet that is high in protein (normal diet for cats) and low in vitamin D and calcium. But the veterinary nutritionist can make sure the diet isn't deficient in the nutrients that cats need to be well.

The bottom line is this: changing the diet to anything else sometimes helps. It just make sense to feed what they should be eating anyway (higher protein, lower carb diet). But is doesn't always help forever. Again, not knowing the underlying cause of the problem makes it difficult to treat.

Mary Ann Farley said...

Dr. Peterson,

My cat, Olive, 4 years old, was diagnosed with IHC during the past year. Her biggest symptom is a complete lack of appetite unless she is getting mirtazapine. My vet has been checking her kidneys every three months, and so far, so good. (I try to give her as little mirtazapine as possible, about 1/8 or 1/4 pill every four or five days, but she seems to be needing it every three days lately.)

She's also been diagnosed as an allergic cat, and her nose breaks out in these weird dark spots, which a fish diet clears up immediately. But now I'm reading that fish is no good. And the brand she eats, Fussie Cat, does have sodium bisulfate, which I read is another acidifier. I do also give her some dry food, which is Orijin Regional Red (all meat), which is 80 percent protein with no acidifiers.

If Olive were your patient, with her appetite being such an issue (she also gets 1/4 tsp Miralax every day for her constipation), would you resort to drug therapy? Or would my next step be a cat nutritionist?

The appetite issue seems to be getting worse, despite her recent bloodwork showing no kidney problems. She's also had all of the other tests to rule out other causes.

Thank you,
Mary Ann Farley
P.S. She has also been diagnosed with bartonella, but I've yet to treat her for that yet. Have you ever seen that being a factor in hypercalcemia?

Dr. Mark E. Peterson said...

Anorexia does not occur in these cats unless the hypercalcemia is severe. Bartellella has not been reported to lead to IC.

If this were my patient, I'd figure out why the appetite is poor and rule out all other causes of hypercalemia (including cancer). Talking to a nutritionist is fine but that's not going to solve the main clinical issue.

The_Cat_Mom said...

Dr. Peterson,

My 11 y/o male tabby cat (neutered) presented with weight loss two years ago, and was at 9.4 lbs. He was diagnosed with kidney disease and hypercalcemia, and prescribed a renal diet (low protein and low phosphorus).

I took my cat in for a checkup after he had lost a bit more weight this past November (down to 8.4 lbs). His kidney values had improved to normal range, but his calcium values remained high. About a week ago I had his vet run the ionized calcium/parathyroid test again, but his ionized calcium came back at 1.6 (it was 1.53 two years ago), and all his other values remained the same as they were in his previous records (no parathyroid issues either). Since his values have been steady over two years, the vet recommended that more than likely, idiopathic hypercalcemia is probably the cause and not cancer, especially since he had full scans done two years ago.

I suspect, however, that his weight loss is due to the hypercalcemia, and his kidney disease was likely caused by the calcium as well rather than the other way around. He is currently on Royal Canin's veterinary diet for kidneys (dry), and Hill's Science Diet k/d for kidney disease as well (wet). He drinks quite a bit of water thanks to a fountain, and is an indoor-only cat.

My question is this: what can I be feeding my cat in order to reduce the ionized calcium levels, increase his weight, and not adversely affect his kidneys? In the event, that is, that the kidney disease is a separate issue from the hypercalcemia. His vet suggested keeping him on the renal food, but I am concerned about the weight loss and not trying to tackle the hypercalcemia with a dietary change.

Thank you so much in advance.

Very sincerely,
Christine C

Dr. Mark E. Peterson said...

No diet will consistently correct the hypercalcemia. If your diet isn't working, then you have to start medical management. Talk to your vet about that.