VITAL Then
To test whether vitamin D or marine-derived long-chain n-3 FA supplementation could protect against autoimmune disease over time, Dr. Costenbader and colleagues piggybacked an ancillary study onto the VITAL trial, which had primary outcomes of cancer and cardiovascular disease incidence.
A total of 25,871 participants were enrolled, including 12,786 men aged 50 and older and 13,085 women aged 55 and older. The study had a 2 × 2 factorial design, with patients randomly assigned to vitamin D 2000 IU/d or placebo and then further randomized to either 1 g/d n-3 FAs or placebo in both the vitamin D and placebo primary randomization arms.
In multivariate analysis adjusted for age, sex, race, and other supplement arm, vitamin D alone was associated with a hazard ratio (HR) of 0.68 (P = .02) for incident autoimmune disease, n-3 alone was associated with a nonsignificant HR of 0.74, and the combination was associated with an HR of 0.69 (P = .03). However, when probable incident autoimmune disease cases were included, the effect of n-3 became significant, with an HR of 0.82.
VITAL Now
In the current analysis, Dr. Costenbader and colleagues reported observational data on 21,592 VITAL participants, a sample representing 83.5% of those who were initially randomized, and 87.9% of those who were alive and could be contacted at the end of the study.
As in the initial trial, the investigators used annual questionnaires to assess incident autoimmune diseases during the randomized follow-up. Participants were asked about new-onset, doctor-diagnosed rheumatoid arthritis, polymyalgia rheumatica, psoriasis, autoimmune thyroid disease, and inflammatory bowel disease. Participants could also write in any other new autoimmune disease diagnoses.
There were 236 new cases of confirmed autoimmune disease that occurred since the initial publication of the trial results, as well as 65 probable cases identified during the median 5.3 years of the randomized portion, and 42 probable cases diagnosed during the 2-year observational phase.
The investigators found that after the 2-year observation period, 255 participants initially randomized to receive vitamin D had a newly developed confirmed autoimmune disease, compared with 259 of those initially randomized to a vitamin D placebo. This translated into a nonsignificant HR of 0.98.
Adding probable autoimmune cases to the confirmed cases made little difference, resulting in a nonsignificant adjusted HR of 0.95.
In contrast, there were 234 confirmed autoimmune disease cases among patients initially assigned to n-3, compared with 280 among patients randomized to the n-3 placebo, translating into a statistically significant HR of 0.83 for new-onset autoimmune disease with n-3.
Dr. Costenbader and colleagues acknowledged that the study was limited by the use of doses intended to prevent cancer or cardiovascular disease and that higher doses intended for high-risk or nutritionally deficient populations might reveal larger effects of supplementation. In addition, they noted the difficulty of identifying the timing and onset of incident disease, and that the small number of cases that occurred during the 2-year observational period precluded detailed analyses of individual autoimmune diseases.
The study was funded by grants from the National Institutes of Health. Dr. Costenbader, Dr. Funk, and Dr. Kremer reported no relevant financial relationships.
A version of this article appeared on Medscape.com.