A day before my 47th birthday last month, I took the subway to Manhattan’s Upper East Side for a coronary artery calcium scan (CAC).For those who haven’t entered the valley of middle age, a CAC is a specialized CT scan that looks for calcium deposits in the heart and its arteries. Unlike in your bones, having calcium in your coronary arteries is a bad thing, because it indicates the buildup of plaque comprised of cholesterol, fat, and other lovely things. The higher the calcium score, the more p...