I have participated in a few studies done by Dr.Montoya at Stanford. Today I got a call from them informing me that my calcium level is high (my level :10.6 , normal range under 10.2) - I was not taking calcium around the time they did the blood draw. A few weeks ago I was talking to them about their heart study, and they told me that some of the participants in that study had higher than normal calcium level,too. On the other hand, a few months ago my annual screening showed a high calcium level; doc ordered a test for parathyroid hormone ( my level 61 - normal level 10-65). Then he tested calcium again and it was high normal this time. Here is what I found on the net today : http://parathyroid.com/parathyroid-symptoms.htm The important point is that 20% of people with parathyroid tumor have normal PTH with high calcium. I have an appointment for blood draw, ordered by my GP , tomorrow to test for cal, and vit D .