May 18, 2015
1 min read

Solar cycles, geomagnetic effects may be linked to giant cell arteritis, RA incidence

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Recorded solar cycles correlated with the onset of giant cell arteritis and rheumatoid arthritis with consistent lag times, according to researchers from Johns Hopkins University, Princeton University and the Mayo Clinic.

The researchers studied medical records from Olmsted County, Minn., that included diagnoses of giant cell arteritis (GCA) made between 1950 and 2004 and of rheumatoid arthritis (RA) made between 1955 and 2007 to compute the yearly average as well as the yearly 3-year centered moving average of incident rates. The incidence rates were adjusted for age and sex based on white people living in the U.S. in 2000.

The AL index, a proxy for the westward auroral electrojet and measure of geomagnetic activity, and the F10.7 index, a measure of solar radiation at the 10.7-cm wavelength and proxy for extreme solar ultraviolet radiation, were used to plot data to represent the solar cycle. Data from the F10.7 index between 1950 and 2007 and the AL index between 1966 and 2007 were obtained from the National Oceanic and Atmospheric Administration (NOAA) Space Weather Prediction Center. Correlational analyses were performed to compare the 3-year moving average of GCA and RA incidence rates with the data from the two indices. Fourier analysis was used to calculate frequencies or periodicities present between 1966 and 2004.

The incidence of GCA on a 3-year moving average correlated with the F10.7 index activity significantly, and peaked with a lag time of 3 years, according to the researchers. Additionally, the 3-year moving average of the AL index with GCA was significantly correlated with a lag time of 1 year or less.

The 3-year moving average of incidence of RA also correlated significantly with the F10.7 index and lagged at 3 years. A positive correlation was also seen with the incidence of RA on a 3-year moving average and the AL index, but the lag time was 5 years to 7 years. Smoothing the 3-year moving average with a 3-year moving Hanning algorithm did not affect the results significantly, according to the researchers. - by Shirley Pulawski

Disclosure: The researchers report no relevant financial disclosures.