It would seem that #2 and #3 directly contradict one another and that the truth is that it does indeed cause cancer at a particular rate / exposure over time.

It would seem that #2 and #3 directly contradict one another and that the truth is that it does indeed cause cancer at a particular rate / exposure over time. Rather than saying it doesn't affect this group but does affect another group it would be more appropriate to establish the level of consumption/exposure that is likely to cause a statistical increase in the likelihood of developing cancer.