The team — led by Joel M. Gelfand, a professor of dermatology and epidemiology — reports the findings in a paper that was published recently in the Journal of the American Academy of Dermatology.
"We know psoriasis is linked to higher rates of diabetes," Prof. Gelfand explains, "but this is the first study to specifically examine how the severity of the disease affects a patient's risk."
Psoriasis and diabetes
Psoriasis is a serious medical condition that affects around 7.5 million people in the United States. It develops from a fault in the immune system that disrupts the normal biology of the skin and joints.
About 80–90 percent of people with psoriasis have plaque psoriasis, an inflammatory condition in which the immune system sends faulty signals that make skin cells grow too fast.
As the cells reach the surface of the skin and die, they form lesions that appear as thick red patches covered with silvery scales. The patches typically develop on the elbows, palms, face, scalp, lower back, knees, and soles of the feet, but they can also affect the mouth, nails, genitals, and other places.
People with psoriasis are more prone to other diseases, including type 2 diabetes, a disorder that develops when the body cannot effectively use insulin. Insulin is a hormone that helps to convert blood sugar, or glucose, into energy for cells.
More severe psoriasis, higher diabetes risk
For their study, Prof. Gelfand and his team used data on two groups of adults — 8,124 with psoriasis and 76,599 without — who were followed for about 4 years.
The data, which came from a survey of general practitioners in the United Kingdom, included a measure of psoriasis severity called body surface area (BSA), which gives the percentage of the body that is affected by the disease. In the U.S., around 20 percent of those with psoriasis have a BSA of 5 percent or more.
From the data, the researchers could see that 3.44 percent (280 people) of the psoriasis group and 2.44 percent (1,867) of the non-psoriasis group were diagnosed with diabetes over the follow-up.
After adjusting for the potential effect of other diabetes risk factors — such as age, sex, and body mass index (BMI) — they found that psoriasis-affected people with a BSA of up to 2 percent had a 21 percent higher risk of developing diabetes compared with those without psoriasis.
But probably the most dramatic result of the study was how psoriasis severity, as measured by BSA, affected diabetes risk.
The results showed that people with psoriasis with a BSA of 10 percent or more had a 64 percent higher risk of developing diabetes compared with people without psoriasis.
In addition, they showed that above 10 percent BSA, the diabetes risk in psoriasis patients relative to non-psoriasis patients went up by another 20 percent for each 10 percent increase in BSA.
"The type of inflammation seen in psoriasis is known to promote insulin resistance, and psoriasis and diabetes share similar genetic mutations suggesting a biological basis for the connection between the two conditions we found in our study."
Prof. Joel M. Gelfand
The researchers propose that in addition to routine targeting of psoriasis patients for diabetes prevention, there should also be routine exams to ensure that those whose disease severity reaches 10 percent BSA or higher are especially targeted.