How is health insurance interstate commerce?

Proponents of the health reform claim that the basis for its constitutionality lies in the commerce clause, the right of congress to regulate interstate commerce. However, insurers are barred from selling policies to people in another state. One of the things that has been debated (although not included) is opening up insurance to interstate competition. So my question is, if health insurance right now is very obviously NOT interstate then how can the commerce clause be used to justify passage of this bill? What interstate commerce are they regulating?
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If you look at it long enough while squinting your eyes just right, then EVERYTHING is "interstate commerce"... That poorly-formulated clause in the Constitution has been abused to extend the Federal control over the States and the Citizens for decades, if not centuries :-(
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