Knitting Lowers Blood Pressure

So I read this once and heard that doctors were prescribing knitting to patients with high blood pressure; however, I had never actually met anyone who was knitting on a doctor's recommendation... until last week. I was buying a knitting magazine and the man behind the counter, probably in his 60s, told me that he was knitting his first sweater. I said something about how it was supposed to lower blood pressure and he said that's why he was doing it. He'd had five heart attacks, something about losing an artery (is that possible?) and blood pressure that was difficult to treat with medication. His doctor was at a loss, so told him to knit. He said so far so good. My blood pressure is so low I'm barely alive, but I don't know if it has anything to do with knitting. Hope the doctor doesn't tell me to quit knitting :)