This is important enough to get it's own article. Note, the next referenced study is just an observational study over time so it lacks cause and effect factors. ref ref This Swedish study found that those taking supplemental calcium who already had a higher food calcium intake, exhibited a higher mortality risk. This risk of death from any cause was two and a half times greater than in those individuals consuming foods with a dietary calcium amount between 600 mg and 999 mg. The high dietary calcium intake was 1400 mg or more.
Supplemental calcium without a high dietary calcium intake did not exhibit increased mortality. A later meta-analysis found slightly different effects for calcium on mortality. ref A case is starting to be built up. ref ref Other articles on this website deal with these.
A serving of dairy has about 300 mg. of calcium. That is the amount in an eight ounce glass of milk. Many glasses hold more than 8 oz. Plus, calcium is added to many other foods, like orange juice, breakfast cereals, and granola bars. It is far to easy to reach 1400 mg of calcium if dairy is consumed.
There are probably a number of factors that influence calcium directions in the body. This next reference talks about the ratio of phosphorus to calcium. ref Phosphorus is also present in many cola drinks. Another vital factor is the balance between calcium and magnesium. Ideally it should be about one and a half to one. Check out magnesium facts here. (especially the CA:MG ratio on colon cancer polyps)
Another aspect for calcium concerns vitamin K2 that guides calcium into proper body areas like bones and keeps it out of arteries and other soft tissues.
Vitamin D also plays a significant role on calcium. Since vitamin D will increase calcium absorption under certain conditions, a already high calcium and or vitamin D dietary intake might be counter productive. article
This is one of the most vital issues that science has to settle NOW.
One point often mentioned in studies is this: Dietary calcium up to a point appears protective while adding extra calcium supplements are potentially detrimental. There is more to the story.