Vitamin D, fish oil ‘unlikely’ to impact RMD progression
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Consuming specific dietary components such as vitamin D or omega-3 is “unlikely to influence the progression” of rheumatic and musculoskeletal diseases, according to a report of systemic reviews published in RMD Open.
“This study brings together the literature on diet and progression of seven RMDs, concluding that research on diet has largely focused on osteoarthritis and rheumatoid arthritis, and there is little evidence suggesting dietary factors can make large differences to the outcomes of people with RMDs,” James M. Gwinnutt, PhD, of the Center for Epidemiology Versus Arthritis at the University of Manchester, in the United Kingdome, and study co-authors, wrote in RMD Open. “This article reports the results of systematic reviews on the effect of diet on progression of RMDs.”
To evaluate the literature investigating the impact of diet on rheumatic diseases, Gwinnutt and co-authors used Medline, Embase and the Cochrane Library to identify studies published between Jan. 1, 2013, and Sept. 18, 2018. The researchers included systematic reviews or meta-analyses of randomized controlled trials and observational studies that included patients with RMDs and investigated the relationship between diet and disease outcome in these patients.
Original studies were included if they employed a longitudinal study design, included adults with RMDs and observed the relationship between dietary exposure and disease progression. The authors did not include abstracts from meeting presentations.
The researchers used AMSTAR-2 to assess risk bias present in systematic reviews and meta-analyses. Additionally, the Cochrane Risk of Bias tool was used to determine the methodological quality of included trials. The authors also used the Grading of Recommendations, Assessment, Development and Evaluations system to determine the quality of evidence put forth by the included literature.
Research was designated as having high quality evidence if it was supported by “meta-analyses of at least five RCTs at low-moderate risk of bias, reporting consistent results without important limitations.” Evidence was rated as low quality if it included few studies with small sample size, or if it had a high risk of bias, the authors wrote.
In all, the researchers included 24 systematic reviews and 150 original articles in the analysis. They investigated 83 dietary exposures, with most of studies focused on patients with rheumatoid arthritis or osteoarthritis. Additional diseases the authors investigated were systemic lupus erythematosus, axial spondylarthritis, psoriatic arthritis, systemic sclerosis and gout.
According to the researchers, evidence for dietary exposure was rated as low or very low in gout, systemic sclerosis, axial SpA and OA.
OA was noted in studies that found moderate evidence in disease progression as it related to diet. The studies included dietary exposure to fish oil, chondroitin, glucosamine and vitamin D, but the effects were small and deemed not clinically relevant by the authors.
Similarly, probiotics, vitamin D and omega-3 demonstrated “moderate quality evidence” and no effects that were clinically significant on disease progression in RA, according to the researchers. In patients with SLE, evidence for fish oil or omega-3s was rated as moderate but had no impact on outcomes. Similarly, fish oil and omega-3s had moderate effect on disease progression but had no impact on outcome, the authors wrote.
“This broad systematic review of 174 published articles shows there is large heterogeneity in the literature on the effects of diet on RMD outcomes, both within and across RMDs,” Gwinnutt and colleagues wrote. “There are many published research studies on RA and OA, investigating a range of dietary exposures. For the other included RMDs, the current evidence base is limited. From the current evidence, there appears to be no single dietary factor which leads to meaningful improvements in RMD outcomes."
“Based on the current literature, health professionals can advise people with RMDs that consuming specific dietary components is unlikely to influence the progression of their RMD, but that it is important to maintain a healthy diet and healthy weight for general health reasons,” they added.
Perspective
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Although this paper reviews the effect of diet on the progression of rheumatic and musculoskeletal diseases as part of a global picture of lifestyle modifications to be undertaken, this is a question that is often brought up at the tail end of a rheumatology office visit. “Doc, what supplements can I take for my arthritis?”
The evidence for dietary supplements is often fraught with controversy. Studies either lack randomization, are low powered, lack active comparators or are sponsored by the makers of the supplements. This review painstakingly addresses the available data, or lack thereof, while helping to shed some light on the issue of supplements and their impact on disease progression.
For the purposes of the review, the authors identified systematic reviews, and meta-analyses for the more obscure supplements and diseases, while excluding more mainstream data such as OA-vitamin E/glucosamine/chondroitin, etc., where sufficient analyses have already been undertaken. RMDs identified for the purpose of the review were RA, OA, SLE, axial SpA with PsA, SSc and gout. Supplements were further subcategorized by diet exposure: Animal products, experimental diets, plant-based interventions, vitamins and minerals.
With this background in mind, a tabular presentation succinctly described the quality/ effect size for each intervention based on the disease state, which I find to be very useful in my daily practice. There is no high-quality data for any intervention in OA, however there is moderate-quality, small-effect-size data for avocado and soybean unsaponifiables in terms of effects on OA pain progression and function. Similar results for glucosamine and vitamin D are noted.
Additionally, it's interesting to note that Curcuma longa had low-quality data with a large effects size regarding progression of OA pain and function. Green lipped mussel extract demonstrated similar effects on OA pain and a low calorie diet seemed to improve OA pain as well.
For RA disease state, there was moderate-quality data but a small effect size for RA pain with fish oil/omega-3, and a large effects size/very low-quality data for ginger with curcumin and black pepper regarding RA disease activity. The reduction of RA pain using the Mediterranean diet is a common dogma.
Data become more challenging to interpret in terms of SLE and SSc, but also surprisingly for gout, where we have often discussed dietary modifications as a core component of care with our patients. In SLE, the authors present very low-quality data with a large effect size for the impact of calcium plus vitamin D on disease activity and cholesterol-lowering education on quality of life. Fish oils/omega-3 seem to improve SLE pain and function.
It was interesting to note green tea extract had a medium effect size/very low-quality data regarding fatigue improvement in SLE — an often challenging area to address. For SpA (PsA and axial SpA), some beneficial effects were noted with marine animal oils/omega-3, and long-chain omega-3 fatty acids on ESR/tender and swollen joint counts. Meanwhile, vitamins C, E and D together improved Rodnan Skin Scores in SSc with a large effect size but low-quality data.
The paper is an engaging summary of the reviews, however the data have drawbacks, such as the risk for publication bias in the studies, a lack of adverse effect reporting, lack of long-term follow-up, low effect sizes for outcomes and the influence of commercial sponsors. No single dietary intervention can be recommended for patients with RMDs, however a healthy balanced diet seems to be the mainstay of medical management.
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