Unseen risk: lifestyle, physical problems may underlie psoriasis link to early mortality.

Severe psoriasis knocks as many years off a person's life expectancy as high blood pressure does, a new study suggests.

Psoriasis is a skin disease that causes an overproduction of skin cells. Most people use topical treatments on the thick patches of skin that develop. But the disease can be itchy and painful, and those with moderate disease often resort to ultraviolet-light therapy. Severe disease can require systemic drugs.

Researchers used a British medical database to track the fates of roughly 138,000 psoriasis patients between 1987 and 2002. Nearly 4,000 had severe disease. To define a large control group, the scientists located the records of up to five other people without psoriasis who were the same age as each patient and who visited the same clinic.

Men and women with severe psoriasis died on average 3.5 years and 4.4 years earlier, respectively, than their counterparts among the controls, the researchers report in the December Archives of Dermatology. That's similar to hypertension's toll, says study coauthor Joel M. Gelfand, a dermatologist at the University of Pennsylvania in Philadelphia.

The researchers adjusted for different rates of heart problems, liver disease, smoking, dementia, cancer, kidney disease, AIDS, diabetes, obesity, arthritis, blood disorders, and ulcers in psoriasis patients and controls. Even so, the researchers found that severe-psoriasis patients were 42 percent more likely to die during the study than the controls. Patients with mild psoriasis showed no increased mortality risk.

The actual cause of the higher death rate is unclear, Gelfand says. Cumulative stresses and depression probably contributed to physical problems in these patients, says dermatologist Gerald G. Krueger of the University of Utah in Salt Lake City. He has noted that psoriasis patients often have unhealthy habits. Their rate of smoking is double the national average, for example. While researchers adjusted for that and other factors in this study, "many patients have a lifestyle that causes them to take on added risks," he says.

At the cellular level, psoriasis causes chronic inflammation, which has been linked to various ailments. Other underlying risks might include sticky platelets in the blood that induce unnecessary clotting or a depletion of blood vessel stem cells that could hamper vascular repair, Gelfand hypothesizes.

The researchers classified patients as having severe psoriasis if the records indicated that they were getting systemic drugs. That definition might be a weakness in the analysis, says dermatologist Robert S. Stern of Harvard Medical School in Boston. Such a group could include people harboring undiagnosed ailments, in addition to psoriasis, who would be prone to seek systemic treatment, he says. Also, severe-psoriasis patients were on average slightly older than the controls. That matters in a mortality study, adjusted or not, he says.

On the other hand, Stern adds, "this is a hard disease to live with." The red, scaly skin patches cause social embarrassment and damage quality of life. "The fundamental finding here is pretty believable," he says.