Solar Activity and Geomagnetic Storms: Do They Affect Health?
There is a large published literature reporting associations between geomagnetic activity and health outcomes — myocardial infarction rates, stroke admissions, blood pressure, heart rate variability, mood disorders and headache — and it is mostly of poor quality. The typical study is an ecological time-series correlation between a geomagnetic index and an aggregate health statistic, with substantial multiple-comparisons exposure, inconsistent lag definitions, and results that fail to replicate across populations. Meanwhile geomagnetic storm variations at ground level are on the order of hundreds of nanotesla against a background field of around 50,000 nanotesla — a fraction of a percent — and no plausible biological mechanism operating at that magnitude has been demonstrated. The reasonable conclusion is not that the effect is disproven but that it is unestablished, and that the confident claims circulating online are far ahead of the evidence.
Here is how to read the field without either dismissing it or being taken in by it.