Does taking one slow-release calcium tablet of 600 mg (such as Citracal) per day pose a risk for heart disease?

Answer:

It depends on how much calcium you are already getting each day from other sources. As discussed in the "Heart attack risk" section of ConsumerLab.com's Calcium Supplements Review, a study determined that the risk of heart attack with calcium supplementation tends to be greater in those already getting more than 805 mg of calcium from their diet (excluding supplements).  

To get an idea of how much calcium is in common foods, see "How much calcium do you already get from food?" section of the report.

It is generally thought that one can't absorb more than about 500 mg of calcium at time, so supplements with higher doses may not be worthwhile. However, an extended-release calcium supplement might help increase the amount absorbed. Nevertheless, 600 mg may still be more than you need.

Too much calcium also increases the risk of kidney stones, and 5% to 8% of men and women have idiopathic calciuria (too much calcium in the urine for unknown reasons), which is a risk factor for kidney stones. Even 600 mg of calcium may be too much for such people, despite a diet somewhat low in calcium, as discussed in the kidney stones section of the report. 

Also be sure you are getting adequate amounts of vitamin D, as it is necessary for your body to absorb and utilize calcium from both foods and supplements. For extensive information about vitamin D, see the Vitamin D Supplements Review.