Excess weight, especially increased fat around the abdominal organs, is a major cause of high blood pressure — at least in people. So it’s only human nature to think the same may be true for our overweight and obese cats. But do extra weight and high blood pressure really go paw-in-paw?
Some research studies suggest the two are linked. Other studies indicate more research is needed. We’ll explain what’s known about this manageable but potentially deadly condition in cats.
A well-recognized condition in cats
High blood pressure, or hypertension, is a common, well-recognized condition in which a cat’s blood pressure is elevated above normal, safe levels. Known as the “silent killer” because there are no early warning signs, high blood pressure can damage a cat’s eyes (retinas), kidneys, heart and brain. That’s why routine physical exams for cats — especially as they become middle-aged and seniors — are so important.
Hypertension in cats is diagnosed in much the same way as it is in people — although it can be a bit trickier. In daily veterinary practice, indirect blood pressure measurements are typically obtained using equipment that measures either the sound of blood moving through blood vessels or the motion of blood through the vessels.
What’s considered “normal” blood pressure for a cat? That’s a really good question, given that blood pressure readings in normal, healthy cats vary tremendously. Breed, cattitude (temperament), cat position at the time of the test, measurement method and operator experience can all influence results. That said, guidelines from the American College of Veterinary Internal Medicine and the International Renal Interest Society recognize a systolic blood pressure (the top number of blood pressure measurements such as 120/80) of less than 140 mmHg as normal for cats.
Causes of high blood pressure in cats
A number of factors may be related with hypertension in cats — but sometimes the cause is unknown. Systolic blood pressure and the risk of hypertension in cats have been found to increase with age. The majority of cats diagnosed with hypertension have other diseases, which may cause or contribute to high blood pressure, although up to 20 percent of cases may not have a clear underlying cause.
High blood pressure secondary to another disease, called secondary hypertension, occurs most often in cats with chronic kidney disease (CKD) and/or hyperthyroidism (overproduction of thyroid hormone). It can also be seen in conjunction with diseases of the adrenal glands, although these are much less common in cats.
According to the International Society of Feline Medicine, chronic kidney disease is the most common condition associated with high blood pressure in cats. Up to 74 percent of cats with hypertension have been found to have increased blood levels of urea and creatinine, two compounds commonly used as indicators of kidney disease. Studies have also shown between 19 percent and 65 percent of cats with CKD experience high blood pressure.
High blood pressure has been documented in 10 percent to 23 percent of cats with hyperthyroidism, although some of those cats may also have had CKD.
So, is there a connection between extra body weight and high blood pressure in cats?
Maybe, maybe not.
In a 2018 study, veterinary researchers at the University of Sydney in Australia evaluated the associations of cat body condition score (BCS) with various health conditions using 10 years’ worth of electronic patient records from a cat-focused clinic in Sydney. Fourteen of the 21 health conditions examined showed significant associations with increased BCS, particularly scores of 7/9 and higher, where an ideal weight is 5 on a 9-point scale. High blood pressure was one of the 14 health conditions showing a significant link to higher BCS.
Veterinarians with the Royal Veterinary College in the United Kingdom also found a significant association between BCS (9-point scale) and systolic blood pressure among 780 apparently healthy cats in their 2017 study. But the results may surprise you. They found that underweight cats (BCS less than 4/9) had significantly lower blood pressure than those that were at an ideal weight or overweight (BCS greater than 6/9). Yet there was no significant difference in the blood pressures of cats of ideal weight compared to overweight cats. The researchers suggested that the low number of overweight cats may have played a role in their findings.
Finally, in a 2018 study, veterinary researchers at the Universidade Federal de Mato Grosso (Federal University of Mato Grosso) in Brazil evaluated various blood constituents known to promote metabolic conditions such as diabetes and cardiovascular diseases including high blood pressure. Samples were obtained from 37 cats, including 15 obese and 12 overweight cats. Cats were considered overweight if their BCS was 6 or 7 on a 9-point scale and obese if their BCS was 8/9 or 9/9. Although the scientists detected positive correlations between systolic blood pressure and some blood lipids, they found no statistical difference between the groups for high blood pressure. They concluded obesity may not be associated with hypertension; however, they also acknowledged more studies with greater numbers of cats are needed.
The take-away?
There is a lot left to be learned about high blood pressure in cats and whether extra weight increases the risk that it occurs. Veterinarians know all too well, however, that high blood pressure is a serious health condition that’s common in cats, especially those with kidney disease and hyperthyroidism. What’s more, veterinarians see overweight and obese cats with health and quality-of-life-compromising conditions every day. The good news is that obesity is preventable and treatable, just as hypertension can be controlled, to provide cats with the quality of life they deserve.
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