When it comes to picking a calcium supplement, it is important to pick one that will absorb at a high rate. Calcium supplements have come a long way since the days of "oyster shell" For years the standard was calcium carbonate, which we now know does not do well in certain ph environments. Then it was calcium citrate, which is okay, but not the best. Calcium hydroxyapatite was considered the best for a long time. And now with much research to back up this claim, we have Advacal. AdvaCAL is the only line of calcium supplements with AAACa calcium, the #1 boneā€“building calcium. AAACa, a patented ionic calcium, has shown statistically significant improvement in bone density in four published human studies. Participants in that research included women and men in their 60s and women in their 80s. In those studies bone density improvement started as early as 4 months, up to 3 years. The average increase over placebo ranged from 2.6% to 3.3% per year in long term studies. A report in the medical journal Osteoporosis International summarized 32 studies conducted between 1977 and 2008 on calcium intake and bone density. The 32 multi-year studies involved 3,169 postmenopausal women, 79 skeletal measures and 7 different types of calcium. AdvaCAL users reported impressive results. With AdvaCAL, average bone density increased +1.5% per year, +3.3% per year compared to a placebo. Calcium carbonate from algae (so-called "algae calcium") has one, unpublished 6-month study available. Participants took algae calcium, strontium, two different levels of bone nutrients and followed a bone-healthy diet and exercise plan. Only one of the two groups showed "improved" bone density. The "improved" group took higher levels of bone nutrients, suggesting that those nutrients may have been more beneficial than the algae calcium. In contrast, participants taking AdvaCAL calcium alone after 4-6 months had impressive increases in bone density in three different studies.without strontium, bone nutrients, exercise or diet changes.