RESEARCH - Geographic variation in RA incidence among women in the US

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Arch Intern Med. 2008 Aug 11;168(15):1664-70.

Geographic variation in rheumatoid arthritis incidence among women in

the United States.

Costenbader KH, Chang SC, Laden F, Puett R, Karlson EW.

Section of Clinical Sciences, Division of Rheumatology, Immunology,

and Allergy, Brigham and Women's Hospital, 75 Francis St, Boston, MA

02115, USA.

BACKGROUND: The geographic variation in rheumatoid arthritis (RA)

incidence in the United States is unknown.

METHODS: We studied residential region from January 1, 1921, to May

31, 1976, and RA risk in a prospective cohort of women, the Nurses'

Health Study. Information on state of residence was collected at

baseline in 1976 (when participants were aged 30-55 years) and on

state of residence at birth, at age 15 years, and at age 30 years in

1992. Among 83,546 participants reporting residence for all 4 time

points, 706 incident RA cases from June 1, 1976, to May 31, 2004, were

confirmed by screening questionnaire and record review for American

College of Rheumatology criteria. Residential region was classified as

West, Midwest, mid-Atlantic, New England, and Southeast. Multivariate

proportional hazards regression models were used to assess

relationships between region and RA risk, adjusting for age, smoking,

body mass index, parity, breastfeeding, postmenopausal status,

postmenopausal hormone use, father's occupation, race, and physical

activity. Analyses were performed in participants who lived in the

same regions, or moved, over time.

RESULTS: Compared with those in the West, women in New England had a

37% to 45% elevated risk of RA in multivariate models at each time

point (eg, state of residence in 1976: rate ratio [RR], 1.42; 95%

confidence interval [CI], 1.10-1.82). In analyses of women who lived

in the same region at birth, age 15 years, and age 30 years, living in

the Midwest was associated with greater risk (RR, 1.47; 95% CI,

1.05-2.05), as was living in New England (RR, 1.40; 95% CI,

0.98-2.00). Compared with living in the West at birth, age 15 years,

and age 30 years, RA risk was higher in the East.

CONCLUSIONS: In this large cohort of US women, significant geographic

variation in incident RA existed after controlling for confounders.

Potential explanations include regional variation in behavioral

factors, climate, environmental exposures, RA diagnosis, and genetic

factors.

PMID: 18695080

http://www.ncbi.nlm.nih.gov/pubmed/18695080

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