Yoga improves the circulation, especially in hands and feet. It boosts blood flow to the cells, and as a result they function better. Inverted postures (it's easy to imagine this) are good because they encourage blood to flow from the legs and pelvis back towards the heart, where it is freshly oxygenated before being pumped out again. (That's why yoga can be very beneficial if you have swollen legs, or kidney problems.)
It has been found to lower 'bad' (LDL) cholesterol, and raise 'good' (HDL) cholesterol, as well as lowering blood sugar. Oh, and did I say that it's effective for bringing down high blood pressure? And for stress? It does this by reducing the levels of cortisol, which is produced by the adrenal glands when we face challenging situations.Yoga is also great for your bones. Osteoporosis is one of the big worries as we age: the prospect of collapsing vertebra (leading to the aforementioned dowager's hump, not to mention terrible pain), or eventually to bones that snap and trigger a fall.