Benefits
Spine bone density in elderly women taking heated oyster shell calcium
In a 2-year double-blind trial in 58 hospitalized Japanese women with a mean age of 80, 900 mg/day of calcium as AAACa (heated oyster shell plus a seaweed ingredient) kept lumbar spine bone density significantly above placebo from month 6 on, while the same dose as calcium carbonate did not differ from placebo. At 18 months, spine density was 106.1%, 99.8% and 90.9% of baseline in the three groups.
Forearm bone density over 4 months with heated oyster shell calcium
In a 4-month double-blind trial in Japanese women, trabecular bone density at the wrist end of the forearm rose to about 106% of baseline with AAACa (900 mg/day calcium) and differed from placebo, while the same oyster shell preparation without the seaweed ingredient, and calcium carbonate, did not. Spine density did not change in any group, and the abstract does not give group sizes.
Calcium absorption of heated oyster shell calcium versus calcium carbonate
In 9 healthy postmenopausal Japanese women tested with stable isotopes after breakfast, about 23% of the calcium from heated oyster shell calcium (AAACa) was absorbed, versus about 15% from refined calcium carbonate. The AAACa tested was mostly calcium hydroxide, the two tests were run a month apart in a fixed order, and no isotope study of plain ground oyster shell was found in PubMed.
Bedtime heated oyster shell calcium and overnight bone breakdown markers
In a 5-day double-blind crossover in 9 healthy Japanese men, heated oyster shell calcium (AAACa) taken as 150 mg of calcium after each meal plus 450 mg at bedtime lowered parathyroid hormone (PTH), and a urinary marker of bone collagen breakdown fell to 40% of baseline, versus 173% on placebo. Taking 300 mg after each meal instead did not lower PTH after 5 days. These are short-term markers, not bone density.
Forearm bone density with electrolyzed oyster shell calcium
In 12 elderly Japanese women in a geriatric hospital given 900 mg/day of calcium as oyster shell electrolysate (oyster shell powder treated with high-voltage electric current), forearm bone density rose from baseline at 12 and 24 months, while it fell in 21 untreated patients. Spine density did not change. There was no placebo group and no between-group test was reported.
Plain ground oyster shell: calcium content and dissolution like refined carbonate
Plain oyster shell calcium is calcium carbonate, which is 40% calcium by weight, so about 1,250 mg supplies about 500 mg of calcium. In lab tests of 27 calcium carbonate tablets, dissolution depended on the amount of filler, not on whether the carbonate came from oyster shell or a chemical precipitate; 63% were less than half dissolved after 90 minutes.
Mechanism of action
Calcium carbonate that dissolves in stomach acid
Ground oyster shell is calcium carbonate. In people with low stomach acid it dissolves less readily, which can reduce absorption unless it is taken with a meal, and calcium supplements in general are absorbed better with food. The share absorbed falls as the single dose rises and is highest at 500 mg of calcium or less.
Heating turns shell carbonate into calcium oxide and hydroxide
Heating oyster shell to about 1,000°C burns off much of its organic matter and leaves mostly calcium oxide. In the AAACa process a heated seaweed ingredient is added, and the final powder is mostly calcium hydroxide. The research group behind AAACa credits this form for its higher absorption; no independent test of that claim was found in PubMed.
Calcium intake and parathyroid hormone
Parathyroid hormone (PTH) rises when calcium supply is short and draws calcium out of bone. In the heated oyster shell trials, PTH was lower with AAACa than with placebo at 12 months, and a bedtime dose lowered the overnight PTH rise and a urinary bone breakdown marker over 5 days. These were marker changes in small groups.
Clinical trials
Dual stable-isotope absorption study. Each woman took a labeled dose of about 300 mg calcium as refined calcium carbonate after a fixed breakfast, then one month later the same test with AAACa, the heated oyster shell and seaweed product. (Uenishi et al. 2010, Nutrients)
10 healthy postmenopausal women in Japan aged 59 to 77; one was dropped from analysis after a 0% absorption value on calcium carbonate.
Fractional calcium absorption was 23.1% with AAACa versus 14.7% with calcium carbonate (p = 0.006), about 1.57 times higher. Blood vitamin D was low (mean 14.2 ng/mL). The AAACa was mostly calcium hydroxide, the comparison salt was pharmacopeia calcium carbonate rather than plain oyster shell, the tests ran in a fixed order, and the co-authors include the researchers behind the AAACa bone trials. The isotopes were supplied by Fujix Corporation; the authors declared no conflict of interest.
Randomized, prospective, double-blind trial: 900 mg/day calcium as AAACa (heated oyster shell plus a heated seaweed ingredient, mostly calcium hydroxide, not plain ground shell) or as calcium carbonate, or placebo, for 24 months on top of a hospital diet supplying about 600 mg calcium a day; all groups then took AAACa in months 25 to 30. The same trial was also published as an 18-month interim report (1995) and a later reanalysis (2004). (Fujita et al. 1996, Calcif Tissue Int)
58 elderly hospitalized women in Japan, mean age 80 (82 in the interim report), in three groups; the 2004 reanalysis describes them as inpatients with osteoporosis.
From month 6 to month 24, lumbar spine bone density relative to baseline was significantly higher with AAACa than with placebo; calcium carbonate did not differ significantly from placebo. At 18 months spine density was 106.1%, 99.8% and 90.9% of baseline. PTH at 12 months and serum alkaline phosphatase were lower with AAACa than placebo. The 2004 reanalysis reports fewer new vertebral fractures with AAACa, but its abstract gives no counts; a 2010 paper by the same group gives 0 of 5, 2 of 7 and 3 of 5 among only 17 of the 58 women with start and end X-rays, far too few to show a fracture effect. One small single-center trial by the developers of AAACa.
Randomized, double-blind trial of AAACa (oyster shell heated under reduced pressure plus a heated algal ingredient), the same oyster shell preparation without the algal ingredient, calcium carbonate (each 900 mg/day calcium) or placebo for 4 months, measured by peripheral quantitative CT and DXA. (Fujita et al. 2000, J Bone Miner Metab)
Women in Japan in four randomized groups; the abstract does not give the number or ages.
Trabecular bone density at the distal radius rose to 106.2% of baseline with AAACa, a significant difference from placebo; the preparation without the algal ingredient and calcium carbonate did not differ from placebo. Cortical density at the mid-radius also rose more with AAACa than placebo. Lumbar spine density did not change significantly. Short trial from the same research group.
Controlled study (indexed in PubMed as randomized) of 900 mg/day calcium as oyster shell electrolysate compared with untreated patients in the same geriatric hospital. (Fujita et al. 1990, Bone Miner)
12 elderly women with osteoporosis given oyster shell electrolysate and 21 untreated controls, Japan.
Radial bone density rose significantly from baseline at 12 and 24 months with oyster shell electrolysate (paired within-group test) and fell significantly in the controls. Spinal trabecular density by quantitative CT did not change significantly in either group. No placebo, and the abstract reports within-group changes rather than a between-group test. Electrolyzed oyster shell is a processed form, not plain ground shell.
Double-blind, placebo-controlled crossover: regimen A, 150 mg calcium as AAACa after each meal plus 450 mg at bedtime; regimen B, 300 mg after each meal; C, placebo; 5 days each. (Fujita et al. 1997, Calcif Tissue Int)
9 healthy male volunteers in Japan.
After 5 days, intact PTH fell by 29 pg/mL with regimen A, versus a rise of 11 with B and 5 with placebo (A vs B p = 0.0242; A vs C p = 0.0433). The urinary collagen breakdown marker Crosslaps was 40% of baseline with A, 97% with B and 173% with placebo (A vs C P = 0.0061). Short-term markers in 9 men, not bone density.