What is the main focus of this passage?

The passage states that scientists previously suspected that a high dietary calcium intake increased the risk of kidney stones. However, Stanford researchers found that a high calcium intake actually decreased the risk of symptomatic kidney stones. This finding is surprising and suggests that there is more to learn about the relationship between calcium and kidney health.
The other options are not the main focus of the passage. The passage does not discuss how Stanford researchers perform studies, how kidney research is conducted, or how kidneys function.