32 million Americans have antinuclear antibodies
MedWire News: Approximately 32 million Americans, or around 14% of the US population, have antinuclear antibodies (ANA), concludes an analysis of data from the National Health and Nutrition Examination Survey (NHANES) 1999-2004.
"Having this large data set that is representative of the general US population and includes nearly 5000 individuals provides us with an accurate estimate of ANA and may allow new insights into the etiology of autoimmune diseases," said study author Frederick Miller (National Institute of Environmental Health Sciences, Bethesda, Maryland, USA) in a press statement.
Miller and team explain that ANA are the most commonly measured biomarkers for autoimmune diseases, such as systemic lupus erythematosus and scleroderma, but their prevalence in the general population is largely unknown because previous estimates were derived from small studies in selected populations.
To generate a nationally representative estimate of ANA prevalence in the USA, the researchers measured levels of the autoantibodies in samples from 4754 participants (aged ≥12 years) of NHANES 1999-2004. They also looked at sociodemographic and behavioral characteristics associated with ANA production.
As reported in Arthritis and Rheumatism, the overall prevalence of ANA was 13.8%. ANA increased significantly with age, and prevalence was significantly higher in men than in women, at 17.8% versus 9.6%.
Based on these findings, Miller and team estimated that 32.3 million people - 21.5 million women and 10.8 million men - had ANA in the USA during 1999-2004.
The female to male prevalence odds ratio (POR) varied considerably across age groups, with no significant between-gender differences in prevalence observed under the age of 30 years, and a peak difference occurring at 40-49 years of age (POR=3.57). This suggests that hormonal factors play a role in the development of ANA, the researchers remark.
Of note, ANA were less common in overweight and obese individuals than in normal weight individuals (POR=0.74 for each group).
The researchers say that this finding was unexpected: "It raises the likelihood that fat tissues can secrete proteins that inhibit parts of the immune system and prevent the development of autoantibodies, but we will need to do more research to understand the role that obesity might play in the development of autoimmune diseases," commented study co-author Minoru Satoh (University of Florida, Gainesville, USA).
By contrast, no significant associations were seen with education, family income, alcohol use, smoking history, current smoking (assessed by serum cotinine), or C-reactive protein.
The majority (84.6%) of ANA detected had a nuclear pattern, cytoplasmic patterns were observed in 21.8%, and nucleolar patterns in 6.1%. The most common specific autoantibodies were anti-Ro (3.9%) and anti-Su (2.4%), which are associated with multiple systemic autoimmune diseases.
Miller and co-authors conclude: "These findings should be kept in mind by physicians when assessing ANA results and will serve as a useful baseline for future investigations of changes in ANA prevalence over time and the factors associated with their development."
By Laura Cowen