Two years after the end of a randomized trial that showed a benefit of daily vitamin D and omega-3 fatty acid (n-3 FA) supplementation for reducing risk for autoimmune diseases, the salubrious effects of daily vitamin D appear to have waned after the supplement was discontinued, while the protection from n-3 lived on for at least 2 additional years.
As previously reported, the randomized VITAL, which was designed primarily to study the effects of vitamin D and n-3 supplementation on incident cancer and cardiovascular disease, also showed that 5 years of vitamin D supplementation was associated with a 22% reduction in risk for confirmed autoimmune diseases, and 5 years of n-3 FA supplementation was associated with an 18% reduction in confirmed and probable incident autoimmune diseases.
Now, investigators Karen H. Costenbader, MD, MPH, of Brigham & Women's Hospital in Boston, Massachusetts, and colleagues reported that among 21,592 participants in VITAL who agreed to be followed for an additional 2 years after discontinuation, the protection against autoimmune diseases from daily vitamin D (cholecalciferol; 2000 IU/d) was no longer statistically significant, but the benefits of daily marine n-3 FAs (1 g/d as a fish-oil capsule containing 460 mg of eicosapentaenoic acid and 380 mg of docosahexaenoic acid) remained significant.
"VITAL observational extension results suggest that vitamin D supplementation should be given on a continuous basis for long-term prevention of [autoimmune diseases]. The beneficial effects of n-3 fatty acids, however, may be prolonged for at least 2 years after discontinuation," they wrote in an article published on January 25 in Arthritis & Rheumatology.
Costenbader told Medscape Medical News that the results of the observational extension study suggest that the benefits of vitamin D "wear off more quickly, and it should be continued for a longer period of time or indefinitely, rather than only for 5 years."
In addition to the disparity in the duration of the protective effect, the investigators also saw differences in the effects across different autoimmune diseases.
"The protective effect of vitamin D seemed strongest for psoriasis, while for omega-3 fatty acids, the protective effects were strongest for rheumatoid arthritis and inflammatory bowel disease," she said.
Mixed Effects
In an interview with Medscape Medical News, Janet Funk, MD, MS, vice chair of research in the Department of Medicine and professor in the School of Nutritional Science and Wellness at the University of Arizona, Tucson, Arizona, who was not involved in the study, saidthat the results suggest that while each supplement may offer protection against autoimmune diseases, the effects are inconsistent and may not apply to all patients.
"I think the VITAL extension results suggest that either supplement (or both together) may have benefits in reducing risk of autoimmune diseases, including possible persistent effects posttreatment, but that these effects are nuanced (ie, only in normal weight post-vitamin D treatment) and possibly not uniform across all autoimmune diseases (including possible adverse effects for some — eg, inverse association between prior omega-3 and psoriasis and tendency for increased autoimmune thyroid disease for vitamin D), although the study was not powered sufficiently to draw disease-specific conclusions," she said.
In an editorial accompanying the study, rheumatologist Joel M. Kremer, MD, of Albany Medical College and the Corrona Research Foundation in Delray Beach, Florida, wrote that "[T]he studies by Costenbader, et al. have shed new light on the possibility that dietary supplements of n-3 FA [fatty acid] may prevent the onset of [autoimmune disease]. The sustained benefits they describe for as long as 2 years after the supplements are discontinued are consistent with the chronicity of FA species in cellular plasma membranes where they serve as substrates for a diverse array of salient metabolic and inflammatory pathways."
VITAL Then
To test whether vitamin D or marine-derived long-chain n-3 FA supplementation could protect against autoimmune disease over time, 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, 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.
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. Costenbader, Funk, and Kremer reported no relevant financial relationships.