A number of studies propose associations between the solar cycle and aging, or for specific age-related conditions. The mechanisms involved are not clear at all, but it is possible to theorize about levels of radiation damage during embryonic development, for example, or the influence of small variations in solar radiation on the operation of metabolism over the long term. Many forms of autoimmune disease are not age-related conditions, but they can be considered forms of damage, so it is interesting to see even speculative data suggesting a correlation with the solar cycle:
Data shows a "highly significant" correlation between periodic solar storms and incidences of rheumatoid arthritis (RA) and giant cell arteritis (GCA), two potentially debilitating autoimmune diseases. The findings by a rare collaboration of physicists and medical researchers suggest a relationship between the solar outbursts and the incidence of these diseases. RA and GCA are autoimmune conditions in which the body mistakenly attacks its own organs and tissues. RA inflames and swells joints and can cause crippling damage if left untreated. In GCA, the autoimmune disease results in inflammation of the wall of arteries, leading to headaches, jaw pain, vision problems and even blindness in severe cases.
Researchers initially spotted data showing that cases of RA and GCA followed close to 10-year cycles. "That got me curious. Only a few things in nature have a periodicity of about 10-11 years and the solar cycle is one of them." When physicists tracked the incidence of RA and GCA cases, the results suggested more than a coincidental connection. The research, which tracked correlations of the diseases with both geomagnetic activity and extreme ultraviolet (EUV) solar radiation, focused on cases recorded in Olmsted County, Minnesota, over more than five decades. The physicists compared the data with indices of EUV radiation for the years 1950 through 2007 and indices of geomagnetic activity from 1966 through 2007. Included were all 207 cases of GCA and all 1,179 cases of RA occurring in Olmsted County during the periods. Correlations proved to be strongest between the diseases and geomagnetic activity.
The findings were consistent with previous studies of the geographic distribution of RA cases in the United States. Such research found a greater incidence of the disease in sections of the country that are more likely to be affected by geomagnetic activity. Although the authors make no claim to a causal explanation for their findings, they identify five characteristics of the disease occurrence that are not obviously explained by any of the currently leading hypotheses. These include the east-west asymmetries of the RA and GCA outbreaks and the periodicities of the incidences in concert with the solar cycle. Among the possible causal pathways the authors consider are reduced production of the hormone melatonin, an anti-inflammatory mediator with immune-enhancing effects, and increased formation of free radicals in susceptible individuals.