Regular thermal therapy, using saunas or hot baths, has the potential to improve impaired insulin sensitivity and boost endothelial expression of the “constitutive” isoform of nitric oxide synthase–effects, analogous to those of aerobic training that should promote vascular health. Previous clinical reports suggest that hot tubs may be beneficial for diabetic control, and that sauna therapy can decrease blood pressure in essential hypertension and provide symptomatic benefit in congestive heart failure. For those who lack ready access to a sauna or communal hot tub, regular hot baths at home may suffice as practical thermal therapy. Thermal therapy might be viewed as an alternative to exercise training in patients too physically impaired for significant aerobic activity. (via.)
Problems such as obesity and diabetes often occur as a consequence of impaired insulin sensitivity. Using the sauna could help restore insulin sensitivity in much the same way as exercise, but without the need for excellent mobility as exercise often demands. Nitric oxide, released from sauna use, acts as a vasodilator. Nitric oxide is often elevated in people living at high altitudes.
Interestingly enough, Viagra actually enhances sexual function in males through some sort of interaction with the nitric oxide pathway.