The similarities between diabetes mellitus in cats and type 2 (adult-onset) diabetes mellitus in humans (T2DM) have been known for many years. In both feline diabetes mellitus and human T2DM, there is a relative deficiency of insulin secretion coupled with insulin resistance. Risk factors for both conditions are similar, including overweight, physical inactivity, and age. There are also some parallel pathophysiological features such as deposition of amyloid in pancreatic islets. The environmental risk factors for T2DM in humans have been extensively studied and are well known, and underlie one of the world's biggest current public health crises.
This case-control study endeavors to identify environmental risk factors that may predispose cats to diabetes mellitus. Patients were identified from the records of a Swedish pet health insurance company. Owners of 396 cats with diabetes mellitus (DM) and 1670 control cats matched on birth year responded to a web-based survey that included questions regarding the cat's breed, age, sex, spay/neuter status, body condition, housing, outdoor access, activity level, diet, eating behavior, feeding routine, general health, stressful events, presence of other pets in the home, medications, and vaccination status. Multiple logistic regression techniques were used to analyze the data.
Cat owner characteristics were similar between diabetic and control groups. Purebred cats represented 19% of the animals, while 81% were mixed breeds. Only 1.8% of the cats were sexually intact. Using univariable analysis, the following findings emerged: (1) when compared with mixed breed cats, Burmese and Norwegian Forest cats were found to have a higher risk of DM, while Persian and Birman cats had a lower risk; (2) factors identified that were associated with a lower risk of DM were rural living environment, female sex, outdoor access, being underweight, living with a dog, and ad libitum feeding; (3) male sex, previous treatments with glucocorticoid injections, primarily dry food diet, being vaccinated, greedy eating behavior, being overweight, not living with animals of other species, and indoor living status were the factors associated with an increased risk of DM.
When the data were analyzed using multiple logistic regression, breed, sex, vaccination status, glucocorticoid injections, eating behavior, and the presence of no other pets in the home besides cats still were found to be associated with an increased risk of DM. Regardless of the type of diet available, overweight cats had an increased risk of DM compared to the cats with normal body conditon. For cats with normal body condition there was an increased risk of DM when the cat consumed predominantly dry food rather than wet food; this is a finding not previously reported. The type of diet was only found to be a risk factor in cats of normal body condition; for overweight cats the type of diet did not seem to matter, suggesting that the DM risk conferred by overweight or obese body condition is greater than that associated with the type of diet.
There was also a correlation between activity level and lifestyle and the risk of DM. The risk of DM was increased for inactive and moderately active cats who stayed indoors only. Those inactive cats who were partially outdoors had a reduced risk of DM relative to those who were indoor only. For active cats, there was no difference in the risk of DM regardless of their lifestyle. This parallels the human experience, wherein physical inactivity reduces insulin sensitivity and also promotes weight gain.
Cats who were described by their owners as greedy eaters had an increased risk of DM compared to those described as nibblers or picky eaters. This is also a new finding in cats. Diabetic people who are "emotional eaters" are known to have poorer outcomes, and it is also known that eating slowly is associated with lower caloric intake and increased satiety in humans. However, it is possible that some of the feline "greedy eaters" in the study were actually experiencing polyphagia prior to being diagnosed with DM.
A history of corticosteroid injections also was a risk factor for the development of DM. Clinicians need to take into cognizance the feline patient's other concurrent risk factors for DM before using glucocorticoid injections, especially in middle-aged, overweight animals. The apparent association between having received vaccines and increased risk of DM may be due to the fact that cats with DM visit the veterinarian more than non-diabetics, and owners of diabetic cats are more likely to be vigilant about their cat's health. These characteristics may also be true of owners who keep their cats wholly or partially indoors. There is certainly no evidence that vaccines predispose to DM in cats, and the percentage of unvaccinated cats in the study population was only 7%. In the same regard, given that less than 2% of the study animals were sexually intact, it is impossible to state that neutering is a risk factor for development of DM. It is possible that neutering may indirectly increase the risk of DM by increasing the risk of obesity in cats due to both an increase in food intake and a decrease in the cat's metabolic rate.
It does appear that the burgeoning incidence of human and feline DM is one of the side effects of civilization. Cats and people with inactive lifestyles that promote weight gain and insulin resistance, who are consuming high carbohydrate diets developed for convenience, and who have fast, greedy eating styles that may be potentiated by stress and boredom, experience similar risk factors for the development of this complicated and potentially life-threatening metabolic disease.
