Hispanic mortality paradox found in RA patients

By Joanna Lyford, Senior medwireNews Reporter

The so-called “Hispanic survival paradox” has been found to extend to patients with rheumatoid arthritis (RA), whereby Hispanic people with the condition tend have more severe symptoms but equivalent mortality to non-Hispanic White individuals.

The researchers who uncovered this phenomenon say that genetic, environmental, and/or sociocultural factors may help explain it, such as the “salmon bias” from foreign-born Hispanics returning to their country of origin late in life, although the precise explanation remains unclear.

It has been shown in several studies that the Hispanic population in the USA has equivalent or lower mortality to that of non-Hispanic Whites, despite having higher rates of diabetes and obesity and lower socioeconomic status.

In the present study, Emily Molina (University of Texas Health Science Center at San Antonio, USA) and colleagues hypothesized that the same paradox would be present among people with RA.

Between 2006 and 2010 they recruited 706 patients with RA, of whom 434 were Hispanic and 272 were non-Hispanic White. They were observed for 6639 patient–years, during which time 229 people died.

Certain baseline characteristics differed between the ethnic groups, report Molina et al. For instance, Hispanic patients tended to be younger at disease onset, had lower socioeconomic status, and were more likely to have diabetes and a high body mass index, but had lower cholesterol levels, blood pressure, and Charlson comorbidity scores.

Hispanic patients also had more severe RA at baseline, as indicated by the tender and swollen joint count and erythrocyte sedimentation rate (ESR), and were more likely to be positive for rheumatoid factor compared with non-Hispanic Whites.

Also, over time, Hispanic patients had significantly more tender and deformed joints, higher ESR, and higher modified Sharp scores than their non-Hispanic White counterparts.

In an unadjusted analysis, mortality over the study period was 2.8 per 100 patient–years in Hispanic patients and 4.7 per 100 patient–years in non-Hispanic Whites. This difference became nonsignificant after adjusting for age and gender, with a hazard ratio of 0.96.

Mortality rates remained equivalent between the groups after further adjusting for baseline differences including socioeconomic status, acculturation, social support, and duration of RA.

However, adding RA manifestation such as ESR and tender and swollen joints and comorbidities to the model caused the difference in mortality to regain significance, with a hazard ratio of 0.57 in favor of Hispanics.

Writing in Arthritis Care & Research, Molina’s group says that the results support the existence of a Hispanic mortality paradox in RA patients.

“Several hypotheses have been proposed to explain this finding, such as migration effects of foreign-born Hispanics, sociocultural effects, or genetic influences,” they write.

“Although we cannot support either the salmon-bias hypothesis or sociocultural effects, it should be of note that after adjusting for RA manifestations associated with greater mortality, the Hispanic mortality advantage increased, despite having worse outcomes on these measures.”

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