Taking daily vitamin D supplements – or a combination of vitamin D and omega-3 fish oil supplements may carry a lower risk of developing autoimmune disease.
Autoimmune disease occurs when the body’s natural defence system mistakenly attacks normal cells. Common conditions include rheumatoid arthritis, psoriasis, and thyroid diseases, which increase with age, particularly among women. The new trial challenges whether the risk of autoimmune disease can be reduced by vitamin D and fish oil supplements.
The researchers said the clinical importance of these findings is high, “given that these are well-tolerated, non-toxic supplements, and that there are no other known effective therapies to reduce rates of autoimmune diseases.”
The trial involving older US adults, published by The BMJ today, also found a more pronounced effect of reduced risk of developing autoimmune disease after two years.
Vitamin D and fish oil supplements
Both vitamin D and omega-3 fish oil supplements are derived from seafood and are known for their beneficial effect on inflammation and immunity. However, no large, randomised trials have tested whether these supplements can lower the risk of autoimmune disease.
To understand the effects of vitamin D and omega-3 fish oil supplements on rates of immune diseases, the research team set out to a clinical trial using 25,871 US adults (average age 67; 51% women; 71% non-Hispanic white).
When they joined the trial, participants provided information on their age, ethnicity, region of residence, income, education, lifestyle, weight, medical history, diet, and current supplement use. Blood levels of vitamin D and omega-3 fatty acids were also measured.
Participants were then randomly allocated to different groups. One group received vitamin D (2,000 IU/day) or matched placebo and another group took omega-3 fish oil supplements (1,000mg/day) or matched placebo. Both reported any diagnosed autoimmune disease over an average 5.3-year period.
These included rheumatoid arthritis, polymyalgia rheumatica (pain and stiffness in the muscles around the shoulders, neck, and hips), thyroid disease, and psoriasis, among others.
Reported cases were confirmed using medical records. Those with insufficient documentation for certainty were classed as “probable” cases.
The results of the study
Throughout the trial, a confirmed autoimmune disease was diagnosed in 123 participants in the vitamin D group compared with 155 in the placebo group – a 22% lower relative rate.
In the omega-3 fatty acid group, 130 confirmed cases were diagnosed compared with 148 in the placebo group (a 15% reduction), but this was not a statistically significant result.
However, when probable cases were included, omega-3 fish oil supplements did significantly reduce the rate by 18% compared with placebo. Furthermore, there was a significant interaction with time which indicated a stronger effect when the supplements were taken for an extended period.
Similar results were found when only the last three years of the trial were considered. The vitamin D group had 39% fewer confirmed cases than placebo, whilst the omega-3 fish oil supplements group had 10% fewer confirmed cases than placebo. Both vitamin D and omega-3 fish oil supplements group decreased autoimmune disease by about 30% versus the placebo alone.
The researchers noted this was a large trial involving a diverse general population with high follow-up rates and treatment adherence. However, they acknowledged that they tested only one dose and formulation of each supplement and said the results may not apply to younger individuals.
The researchers confirmed that this is the first direct evidence that daily supplementation with either agent – or a combination of vitamin D and omega-3 fish oil supplements – for five years among older US adults reduces autoimmune disease incidence, with more pronounced effect after two years of supplementation.
“We are continuing to follow participants for two years in an extension study to test the time course of this autoimmune disease reduction effect,” they noted. “Further trials could test these interventions in younger populations, and those with high autoimmune disease risk.”