This question was brought up in my dojo. The reply in class was "Depending on how someone practices sanchin, their blood pressure will be elevated to different degrees. Harder sanchin (goju and some uechi schools) will increase systolic blood pressure significantly. So anything that affects blood pressure or blood viscosity will have more detrimental effects on not only the practitioner but the quality of the sanchin. (this can be anything from presence or absence of medications, caffine, high amounts of glucose in the blood, high levels of triglycerides...) Plus a higher systolic blood pressure can mean what ever was floating in the individuals blood stream will make its way into the lymph, then to the sweat." I haven't seen the last side effect with softer sanchin, or other katas.
Is any one willing to share what they do before hitting the dojo? Any thogts on it?
I am no expert, and I'm certainly not a doctor, so this is not medical advice.
However, when I started training in karate two years ago, I weighed nearly 300 pounds. I could not run a mile without stopping. I had borderline high blood pressure at 140/90, my cholesterol was terrible, and my blood sugar, although I did not know it, was over 300.
Now I weigh 60 pounds less, I can run, my blood pressure is 110/70, my cholesterol is fine, and my blood sugar is 100.
The doctor says I could not have done the blood pressure or the cholesterol lowering by the simple act of taking my diabetes medication; that only lowers blood sugar. I believe that karate has been responsible for the rest.
Our first kata is Sanchin, so I've been doing it (Goju style as practiced in Isshin-Ryu) for two years. It has done me no harm.
I might suggest the excellent book,
The Way of Sanchin Kata: The Application of Power
by Chris Wilder.
It's not very expensive on Amazon, but it's an eye-opening read. Of course it is no substitute for learning Sanchin in a dojo, but it's an excellent substitute.
In summary, no I do not believe that Sanchin, properly done, is harmful. Iron Palm I have no idea about, but that sounds like a bunch of hooey to me.