Cystitis just means ‘inflammation of the bladder’ and can be caused by many things. Many cases of ‘cystitis’ affect not only the bladder, but the urethra as well, so in cats we tend to refer to FLUTD – Feline Lower Urinary Tract Disease. This is a range of syndromes and diseases that produce the same clinical symptoms. 

What are the causes of cat cystitis?

Cats are unusual in that the vast majority of cases of cystitis in cats are sterile- i.e not caused by bacteria. Instead, most cats suffer from ‘idiopathic cystitis’ – inflammation without a known cause. This is thought to be linked to stress, as cases often follow a change in the cat’s living environment, such as building work or the arrival of a new pet. Some cats also have bladder stones or crystals. All of these diseases cause similar symptoms – little and often urination, blood in the urine, sometimes stopping of the urine flow altogether. It’s an exercise in ruling out each cause one-by-one to find out which is causing a problem for your cat. If bacteria have been ruled out using a culture and stones have been ruled out using microscopy, then idiopathic cystitis is the most likely cause. 

Why is cranberry juice supposed to help?

Cranberry juice has long been advocated for help in human cystitis. Theories as to why it works include that the juice makes the urine more acidic and therefore stop bacteria from growing, and chemicals made by the cranberries (called proanthocyanidins) stop the bacteria from sticking to the bladder wall. Evidence in petri dishes and test tubes has shown that it doesn’t stop bacteria from growing, but it does stop certain bacteria from sticking, meaning they’re more likely to be ‘flushed’ out during urination. 

What is the evidence that cranberry juice helps?

In humans, there is some evidence that cranberry juice helps in cases of recurrent urinary tract infections in young, non-pregnant women by stopping a particular type of pathogenic E. coli from sticking to the urinary tract. However, a recent large assimilation and comparison of several big studies (the Cochrane Review) found that, on the whole, cranberry juice didn’t seem to help, perhaps because there are so many different juices and supplements with different amounts of cranberry, and so many different causes of cystitis than this one very particular E. coli.

There’s some evidence that these (proanthocyanidin) chemicals have the same effect on canine and feline kidney cells as they do on human bladder cells. But there’s not yet much to prove that it actually works to prevent E. coli infections. And since infections tend to occur in the bladder and urethra, we don’t even know if cranberries have this ‘non-sticky’ effect on feline bladder cells.

Remember, also, that cats rarely get bacterial cystitis, so any minor effect in humans is likely to be even less noticeable in cats.

Is there any evidence that cranberry juice harms?

Of course, if a supplement doesn’t do any harm then you might feel it’s worth trying. Currently there are no reports of cranberry toxicity in cats. However, there is a theory that the high amount of chemicals called oxalates in cranberries could cause crystals in the urine (this has been shown in humans), so if your cat has been suffering from crystals in the urine this could in fact make the situation worse. This may be compounded by the fact that a change in the urine pH to be more acidic makes some crystals more likely to form.

What about other supplements for urinary health?

There are hundreds of urinary supplements out there, with varying ingredients and varying levels of clinical evidence. However, there is no evidence that many of these supplements work. For instance, glucosamine has been often recommended for feline cystitis. One study suggested that cats with cystitis have lower amounts of glycosaminoglycan proteins than healthy cats, and that it was possible to supplement enough glucosamine orally to make a difference to this. However, it didn’t show that this then prevented cystitis or treated cystitis. One recent study by a feline specialist showed no difference in recovery between patients treated with a glucosamine supplement and those that were not.

The best evidence for effect on FLUTD in cats is in fact through environmental modification. This could include changing a cat’s routine, providing more hiding places, encouraging hunting behaviours and increasing access to resources in order to reduce stress. Studies on this are still in the early stages and there aren’t many published, but so far the results are promising. The same goes for feline facial pheromone therapy (Feliway), which so far has suggested that treated cats suffer fewer days with cystitis.

What’s the bottom line?

As with many things in veterinary medicine, the bottom line is that we don’t know much. There is a huge gap in clinical evidence in this area, and until proper studies with hundreds of patients and lots of veterinary practices have been completed, we can’t say for sure. The evidence we have at the moment suggests that it doesn’t help, but that it doesn’t harm either. However, you should be cautious about using it if your cat could have urinary crystals, so a visit to the vet first for a proper work up and diagnosis is sensible in the first instance. 

Fact or myth? Probably myth.