No kidding, that's the title of the Medscape (doctors' chat room?) forum on the recent news that calcium supplementation over 1400 mgs. daily or low calcium intake (600 mg or less) are both associated with increased risk of death. Admittedly the study's methods were observational, meaning that they can identify an association but not that it's causative. Medscape can't theorize why it would be causative, but I would hazard a proposal. Increased extra body calcium in the presence of inflammation (true for most people eating a standard American diet) and with a relative deficiency of vitamin K2 (partly responsible for directing calcium towards the bones and away from blood vessels and tendons) might tend to see calcium deposits in unwanted areas, such as coronary and cerebral vessels, resulting in cardiovascular disease and stroke. We can't measure vitamin K2, but if you ask most people on a conventional diet they avoid its best sources: cheese (too much fat) and fermented foods (no palate for that), enjoying perhaps only its one palate acceptable source: beer.
Not that I disagree with the conclusion: in general, calcium supplementation has little evidence for benefit and accruing evidence for possible harm. The proposed benefit for calcium supplementation is reduced risk of fracture, but that can also be achieved with simple normalization of vitamin D levels, allowing you to absorb calcium from almost any way of eating. The possible hazards of high dietary calcium and/or added calcium are mitigated somewhat by regular consumption of multi-vitamins, depending on whom you ask. Confounding factors, or course, are that most people who take supplements on a regular basis self-describe and legitimately qualify as good to excellent in their overall health.
Surprisingly, perhaps, is the observation that quite low total calcium intakes, of less than 600 mg daily, was also associated with cardiovascular mortality. My hypothesis for that observation would be that it's hard to eat a well-balanced diet with less than 600 mg of daily calcium: no dairy products isn't hard to imagine, but you'd have to also eliminate almonds, leafy green vegetables, calcium-fortified foods, broccoli, salmon ... you get the idea that a low calcium diet may not be well-balanced and healthy in other ways besides its calcium content.
My take-away message from this conundrum is that the bone-forming supplements to focus on do not include calcium - get that from food - but do include vitamin D3 sufficient to normalize your blood levels, vitamin K2, adequate protein and a daily dose of weight-bearing activity. (I'll get up from my computer at this point and walk around the room....ok, I'm back.) Note that vitamin K2 does not affect blood clotting, so is safe for people on blood thinners to take, 200 mcg daily of vitamin K2 as MK7.