Vitamin D has immunomodulatory properties with potential etiologic implications for autoimmune diseases. The relevant exposure time during which vitamin D may influence disease risk is unknown. Our objective was to examine the relationship between reported vitamin D intake during adolescence and adult-onset rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) incidence in prospective cohort studies of women, the Nurses' Health Study (NHS) and the Nurses' Health Study II (NHSII).
Food frequency questionnaires concerning high school diet completed by 73,629 NHS (1986) and 45,544 NHSII (1998) participants were used to calculate nutrient intakes during adolescence. Incident RA and SLE cases prior to 2006 (NHS) and 2007 (NHSII) were confirmed by medical record review. Cox proportional hazards models calculated relative risks and 95% confidence intervals of incident RA and SLE according to quintile cutoffs of vitamin D intake. Age- and calorie-adjusted and multivariable-adjusted (including sun exposure factors) analyses were completed. Random-effects models were used to meta-analyze estimates of association from the 2 cohorts.
Incident RA was confirmed in 652 NHS and 148 NHSII participants and SLE was confirmed in 122 NHS and 54 NHSII participants over a mean followup time of 351 months (NHS) and 209 months (NHSII). Age- and calorie-adjusted and multivariable-adjusted models did not show significant associations between adolescent vitamin D intake and risk of adult-onset RA or SLE.
We did not find associations between adolescent dietary vitamin D intake and adult RA or SLE risk among NHS and NHSII women, suggesting that other time periods during the life course should be studied.