Systematic Review Highlights Inconsistent Evidence on Role of Diet in RA Risk

Researchers are highlighting the need for more clarity on how different eating habits affect the risk of rheumatoid arthritis (RA) based on their recent findings from a systematic literature review, published in Seminars in Arthritis and Rheumatism.

Although data pulled from nearly 20 cohort-based studies and 8 case-control studies showed several trends, the research lacked consistent evidence, had heterogenous study designs, and varied in methods of assessing diet.

“Our systematic review highlights the complexity of the area and clearly shows that there is a lack of consistent evidence on the role of diet in the development of RA. We believe that this is mostly due to differences in study quality and methodology,” commented the researchers. “The differing results may also partly be explained by the paucity of high-quality studies in the area.”

Three of the case-control studies were considered good quality, and 5 were considered poor quality, some due to lack of validation of the methods to assess diet. Among the cohort studies and a nested case-control study, 10 were considered good quality, 7 fair quality, and 2 poor quality.

Generally, the studies suggested a decreased risk of RA associated with fish and vegetable consumption, as well as Mediterranean-style diets, although the researchers noted that these studies used varying methods and had varying results.

For example, data from 3 case-control studies deemed poor quality consistently suggested protective effects of fish against RA, whereas the cohort-based studies considered good quality indicated more variability. Some of these studies showed a decreased risk of RA associated with fish intake while others showed an increased risk associated with medium-fat fish.

Among the studies that included data on fish intake, one accounted for the presence of smoking, finding that a higher frequency of fish intake was associated with a less elevated risk of RA. Among ever-smokers who ate fish less than once a month, there was a significant increase in risk of RA beginning at 55 years and younger (HR, 2.59; 95% CI, 1.65-4.06) while ever-smokers who ate fish once or more a month had a slightly increased risk (HR, 1.29; 95% CI, 1.07-1.57) compared with people who had never smoked.

“A vast majority of the included studies have accounted for several important confounding variables. Smoking is a well-established risk factor for RA, and also associated with diet as well. Thus, adjustment for smoking is appropriate in studies examining the relation between diet and RA,” described the researchers. “Another important confounding factor, that should be accounted for in nutritional epidemiology studies, is total energy intake, which can affect the relation between diet and disease risk in several ways. It may be a proxy for level of physical activity, which can affect the risk of RA.”

Noting conflicting data on the relationship between red meat and the risk of RA, the researchers wrote of their findings from a cohort-based study considered fair quality, which showed that eating red meat was associated with an increased risk among women 55 years and younger. With the consumption of red meat having been associated with fat accumulation and inflammation, the researchers noted that red meat could result in adipose tissue and subsequent systemic inflammation, leading to the development of RA. No other associations between red meat intake and RA risk were apparent among the other studies.

Reference

Bäcklund R, Drake I, Bergström U, Compagno M, Sonestedt E, Turesson C. Diet and the risk of rheumatoid arthritis – a systematic literature review. Semin Arthritis Rheum. Published online October 28, 2022. doi:10.1016/j.semarthrit.2022.152118