Adherence to a healthy diet did not reduce the risk for developing systemic lupus erythematosus (SLE), analysis of data from the Nurses’ Health Studies found.

Compared with women who scored in the lowest tertile of the 2010 Alternative Healthy Eating Index (AHEI-2010), those in the highest tertile had no significant decrease in lupus risk, with a hazard ratio of 0.78 (95% CI 0.54-1.14, P=0.23), according to Medha Barbhaiya, MD, of the Hospital for Special Surgery in New York City, and colleagues.

There also was no difference in risk depending on whether the individual was seropositive for anti-double stranded (ds)DNA antibodies (HR 0.78, 95% CI 0.45-1.36) or seronegative (HR 0.78, 95% CI 0.47-1.31), the researchers reported in their study online in Arthritis Care & Research.

Multiple studies have demonstrated lower risks of rheumatoid arthritis with healthy diets such as the 2010 Alternative Healthy Eating Index (AHEI-2010), but the association of overall dietary pattern has been little studied in SLE.

Nonetheless, there are mechanistic rationales for considering diet as a potential influence on SLE risk: “Oxidative stress and other environmental exposures, including diet, can contribute to lupus onset and flares through epigenetic mechanisms that modify CD4+ T cell gene expression,” Barbhaiya and colleagues explained.

To explore this, they analyzed data from the two Nurses’ Health Studies, including 79,568 women enrolled in the first study from 1984 to 2012 and 93,554 in the second study from 1991 to 2013.

Participants filled out a food frequency questionnaire every 4 years, and were rated according to adherence to three dietary quality scores. The AHEI-2010 is based on the 2010 Dietary Guidelines for Americans and includes 11 foods such as fruits, vegetables, and whole grains that are considered healthy and others such as sugar-sweetened beverages (including fruit juice), red/processed meat, trans fat (% of total energy), and sodium intake considered unhealthy. Scores range from 0 (worst) to 110 (best).

A second diet was the modified Mediterranean diet, which measures nine components including vegetables, fruits, nuts, whole grains, legumes, and fish as well as undesirable components including saturated fats and red or processed meats; scores can range from 0 to 9. A third type was the Dietary Approach to Stop Hypertension (DASH) diet, which is similar to the Mediterranean diet but with scores ranging from 8 to 40.

A fourth dietary evaluation used the Empirical Dietary Inflammatory Index, which rates food groups according to plasma inflammatory biomarker levels including C-reactive protein and interleukin 6. Nine food groups were considered pro-inflammatory, including processed meats, refined grains, and high-energy beverages, while nine others were considered anti-inflammatory, including dark yellow and leafy green vegetables.

The analysis was adjusted for multiple factors, including age, race, income, smoking, alcohol use, menopausal status, and body mass index.

There were 194 incident cases of SLE, with 91 being anti-dsDNA positive and 103 anti-dsDNA negative. Mean age for the participants was 50, more than 90% were white, and mean body mass index was 25.

On multivariable analyses, there were no significant differences in SLE risk for the averaged highest versus lowest tertiles of scores on the three scores other than the AHEI-2010:

• Mediterranean diet, HR 0.82 (95% CI 0.56-1.18)

• DASH diet, HR 1.16 (95% CI 0.81-1.66)

• Dietary inflammatory index, HR 0.83 (95% CI 0.57-1.21)

There also were no differences according to anti-dsDNA status on any of the scores, or in baseline scores.

The only lower risk identified was on cumulative average intake of nuts and legumes in the AHEI-2010, with a hazard ratio for SLE risk of 0.59 (95% CI 0.40-0.87, P=0.006) for the highest versus lowest tertile. “Nuts and legumes are a rich source of alpha-linoleic acid, an anti-inflammatory polyunsaturated fat associated with reduced risk of inflammation and cardiovascular disease,” the researchers explained, adding that the 41% decreased risk for SLE seen with high intake of nuts and legumes should be investigated further.

As to why the researchers were unable to detect associations between dietary quality and SLE, they suggested there may have been changes in secular trends in lifestyle and diet over the years of the two studies, and that diet in early life may be more influential (the youngest dietary assessment in this analysis was at age 27). The study also was not powered to evaluate interactions between diet and other potential risk factors such as current smoking.

An additional limitation was the possibility of recall bias with the food questionnaire.

“Our findings warrant replication in large, prospective, general population cohorts, with younger participants and increased racial/ethnic variation,” Barbhaiya and co-authors concluded.