Vigorous physical activity – particularly running and aerobics – appears to protect women against developing psoriasis, according to a report published online May 21 in the Archives of Dermatology.
In what the researchers described as the first prospective study to examine the association between physical activity and the onset of psoriasis, women who reported participating in at least 20.9 MET (metabolic equivalent)–hours per week of vigorous exercise – the equivalent of 105 minutes of running or 180 minutes of swimming or playing tennis – showed a 25%-30% lower risk of incident psoriasis, compared with women who reported no vigorous exercise, said Hillary C. Frankel of the department of dermatology at Brigham and Women’s Hospital, Boston, and her associates.
In this study, women who reported participating in at least 20.9 MET hours per week of vigorous exercise showed a 25%-30% lower risk of incident psoriasis.
"This amount of vigorous activity is roughly equivalent to the current U.S. Department of Health and Human Services recommendation for greater health benefits," they noted.
Physical activity has been associated with a decreased risk of several disorders that are characterized by systemic inflammation, including type 2 diabetes, colon cancer, coronary artery disease, and breast cancer. Until now, only a few cross-sectional studies have examined the role of physical activity in psoriasis, and those have yielded inconsistent results.
Ms. Frankel and her associates prospectively assessed the relationship between customary physical activity and incident psoriasis using data from the Nurses' Health Study. That study included a longitudinal cohort of more than 116,000 female registered nurses residing in 15 states who were aged 25-42 years at baseline in 1989, and who completed biennial questionnaires about their health.
For this study, the researchers focused on 86,665 participants who did not have psoriasis at baseline and who answered detailed questions about their physical activity in 1991, 1997, and 2001. This included 1,026 study participants who developed psoriasis during the 14-year follow-up period.
The total physical activity score, measured in MET-hours per week, was inversely related to the risk of developing psoriasis in a dose-dependent fashion. The most physically active quintile of the cohort had a relative risk of 0.71 of developing psoriasis, compared with the least-active quintile.
In a separate analysis by type of physical activity, only certain vigorous physical activity was found to be protective against psoriasis.
After adjustment for age, smoking status, alcohol intake, and other vigorous activity, women who ran for more than 1 hour per week had a relative risk of 0.37, compared with those who did not run. Similarly, women who participated in at least 4 hours per week of aerobics had an adjusted relative risk of 0.54, compared with those who did not do aerobics. Both trends were statistically significant.
However, no such association was seen among women who participated in other vigorous activities such as bicycling, swimming, and playing tennis. And walking – regardless of the amount of time devoted to it – was not associated with reduced risk of psoriasis.
"The highly variable intensity at which these activities are performed may account for this finding," the investigators said (Arch. Dermatol. 2012 May 21 [doi:10.1001/archdermatol.2012.943]).
The mechanism by which vigorous exercise might reduce psoriasis risk is not yet known, but "it is biologically plausible that [it] could modulate a state of chronic inflammation and/or immune activation that predisposes women to develop psoriasis," Ms. Frankel and her colleagues said.
Physical activity is known to lower levels of proinflammatory cytokines and elevate levels of anti-inflammatory cytokines. It also has beneficial effects on mood, decreasing anxiety and stress; stress is believed to incite psoriasis by activating the immune system, they added.
This study was supported by the National Institutes of Health and the department of dermatology at Brigham and Women’s Hospital. Study coauthor Dr. Abrar A. Qureshi reported ties to Novartis. No other potential financial conflicts of interest were reported.