Taking vitamin D and fish oil supplements reduced the risk for autoimmune diseases — a group of disorders that includes type 1 diabetes — over a five-year period, according to a new study presented virtually at ACR 2021, the annual meeting of the American College of Rheumatology, and described in an article at Medscape.
The study, which enrolled 25,871 adults (12,786 men ages 50 and over, and 13,085 women ages 55 and older), was designed to study the effects of taking vitamin D and fish oil supplements on the risk for cancer and cardiovascular disease — but researchers also looked at a variety of other outcomes in participants, including new diagnoses of autoimmune diseases. Participants were randomly assigned to take either 2,000 IU per day of vitamin D or a placebo (inactive pill), and again to take either 1 gram per day of omega-3 fatty acids from fish oil or a placebo. This means that, in the end, there were four different study groups — those taking two placebos, those taking one placebo and either vitamin D or fish oil, and those taking both vitamin D and fish oil.
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Taking vitamin D, fish oil supplements linked to reduced risk for autoimmune disease
Participants continued to take their assigned pills for five years, and self-reported any autoimmune diseases to the researchers during this period. When possible, these reports of autoimmune diseases were confirmed by medical records or measurements of disease markers. At the end of the study period, there had been a total of 123 people in the vitamin D group with at least one autoimmune disease, compared with 155 in the placebo group (for vitamin D) — representing a 22% reduction in the risk for autoimmune diseases from taking vitamin D. There were 130 people in the fish oil group who developed at least one autoimmune disease, compared with 148 in the placebo group (for fish oil) — representing a 15% reduction in the risk for autoimmune diseases from taking fish oil, which wasn’t statistically significant due to the smaller difference and fairly low number of people in each group who developed an autoimmune disease.
Statistically, the researchers found no evidence of interaction between the two supplements — meaning that there wasn’t any apparent combined effect from taking both supplements that was greater, or less, than the sum of each individual effect. But they did observe an interaction between vitamin D and body-mass index (BMI, a measure of body weight that takes height into account), with a stronger protective effect against autoimmune diseases seen in people with a lower BMI.
When the researchers adjusted for participants’ age, sex, race, and whether they took the other supplement or a placebo (in place of that other supplement), the researchers found that taking vitamin D was linked to 32% reduction in the risk for autoimmune diseases, compared with taking a placebo. Taking fish oil was linked to a nonsignificant 26% reduction in the risk for autoimmune diseases. Taking both supplements together was linked to an overall 31% reduction in the risk for autoimmune diseases.
The researchers concluded that for many older adults, taking vitamin D and fish oil supplements could significantly reduce the risk of developing autoimmune diseases. Limitations of the study included the study population of only older adults, and the fact that participants weren’t considered to be at high risk for autoimmune diseases. In people with a family history or increased genetic risk for autoimmune diseases, the researchers noted, the benefits from these supplements could be greater.