Researchers have found that Vitamin D and marine omega-3 fatty acids -- also known as fish oil -- are not effective at reducing systemic inflammation.

The study, published in the journal Clinical Chemistry is an analysis of the Vitamin D and OmegA-3 TriaL (VITAL) by investigators at Brigham and Women's Hospital in the UK. "People commonly think that these supplements can prevent inflammatory diseases, but when a patient asks their doctor, 'Should I take this supplement?' "Doctors often don't know what to advise because there haven't been large scale clinical trials. VITAL provides a large dataset to address these questions," said author Karen Costenbader. The VITAL study is a random, double-blind, placebo-controlled trial in which researchers tested the effects of supplements of vitamin D (2000 IU/day), omega 3s (1 gm/day) or both.

For this analysis, they tested levels of three known biomarkers of inflammation at the start of the trial and after one year of taking supplements or a placebo. The authors analysed biomarkers for only a subgroup of the original trial's population -- approximately 1,500 of the over 25,000 participants. They were interleukin-6 (IL-6), tumour necrosis factor-receptor 2, and high sensitivity C-reactive protein (hsCRP). The team found that neither supplement reduced the biomarkers at one year. Surprisingly, among those taking the vitamin D supplement, instead of decreasing, IL-6 levels rose by 8.2 per cent.

The researchers reported that among participants who had lower fish intake at the start of the trial, hsCRP levels did decline for those taking the omega-3 supplement. "We see that people whose fish intake was low at baseline had a reduction in one of the biomarkers of inflammation," said Costenbader.