Current smoking is associated with incident ankylosing spondylitis -- the HUNT population-based Norwegian health study.

OBJECTIVE

Smoking contributes to progression of ankylosing spondylitis (AS). Because smoking is also a risk factor for incident rheumatoid arthritis (RA) and psoriatic arthritis, our aim was to test whether smoking habits are associated with incident AS.

METHODS

Using data from the HUNT health study of the entire adult population of Nord-Trøndelag, Norway, participants in HUNT2 (1995-1997) and HUNT3 (2006-2008) were identified who reported a diagnosis of AS in HUNT3 but not in HUNT2 (n = 107). Incident AS cases were compared with AS-unaffected individuals (n = 35,278) in a case-control design. Participants with RA were excluded.

RESULTS

Present smoking was significantly associated with incident self-reported AS in logistic regression adjusted for potential confounders (OR 1.99, 95% CI 1.28-3.11, p = 0.002). Previous smoking (OR 1.15, 95% CI 0.66-2.02, p = 0.62) or total pack-years at HUNT2 (OR 1.01, 95% CI 0.99-1.04, p = 0.21) were not significant. The association with present smoking remained significant in various sensitivity analyses: including only cases with high probability of true AS diagnosis (OR 1.82, 95% CI 1.03-3.19, p = 0.04); including only cases with AS reported more than 3-5 years after HUNT2 (OR 2.34, 95% CI 1.09-5.03, p = 0.029), or including only participants genotyped for HLA-B27 (94 cases and 859 controls) adjusting for genotype (OR 1.79, 95% CI 1.04-2.85, p = 0.033). Hypertension was also significantly associated with incident AS (OR from 1.65 to 2.81).

CONCLUSION

In the HUNT population-based study, incident AS was associated with current smoking and hypertension. If verified in further studies, this suggests that smoking should be discouraged in those at a higher AS risk, e.g., with a family history or carrying HLA-B27.