Calcium hazards and bioavailability

Diverse Calcium opinions
The inorganic forms:
The organic forms:

Diverse Calcium opinions

Consensus:

Calcium Carbonate is the lowest cost, requires the most stomach acid to be digested, and is probably less bio-available
Bio-availability of the Calciums range by perhaps 10X (however, Wikipedia reference below says otherwise)
If you must take a lot, take it several times per day – 600 mg at a time
- As with Magnesium the body can absorb only so much at a time
- Unsure if there is a 600 mg limit when taking <3,000 IU of vitamin D
- Vitamin D increases absorption of Calcium: 20% - 50%

Likely: Avoid rock-calcium, especially if senior

Calcium sources that do not need stomach acid, such as milk and some plants, are probably the most bio-available
Not often seniors have less stomach acid, so will not get as much from Calcium Carbonate as younger people

Personally, I use the Algae Calcium powder from Amazon
I put the powder in a modified salt shaker, and shake in on my morning cereal

Plant-based Calcium probably better than rock-based

Calcium level for adults is 8.5 to 10.2 mg/deciliter

which is 2.15 to 2.55 millimoles/liter Cleveland Clinic

Calcium and Vitamin D category listing has 226 items

See VitaminDWiki

Calcium supplements increases the chance of dying by 1.4 X - June 2022

Calcium Supplementation, Risk of Cardiovascular Diseases, and Mortality: A Real-World Study of the Korean National Health Insurance Service Data
Nutrients 2022, 14(12), 2538; https://doi.org/10.3390/nu14122538
by Jae-Min Park 1,2,†ORCID,Bora Lee 3,†,Young-Sang Kim 4ORCID,Kyung-Won Hong 5ORCID,Yon Chul Park 6,Dong Hyeok Shin 7,Yonghwan Kim 8ORCID,Kunhee Han 9,Kwangyoon Kim 10,Junghwa Shin 10,Mina Kim 11ORCID andBom-Taeck Kim 10,*

Few studies have investigated the effects of calcium supplementation on cardiovascular outcomes in individuals with low calcium intake in real-world settings. This study examined the association between calcium supplementation and cardiovascular outcomes in the Korean population in a real-world setting. This large retrospective cohort study included patients aged ≥45 years first prescribed calcium supplements in 2010. Age- and sex-matched controls were recruited among those who had no prescription for calcium supplements. Longitudinal data were collected on 31 December 2018. Kaplan–Meier estimation and Cox proportional hazard regression analysis were performed. The cumulative incidence of acute myocardial infarction, ischemic stroke, and death was significantly higher in the calcium supplementation group than in the control group (p < 0.05 by log-rank test). The calcium supplementation group had a significantly higher risk of myocardial infarction, ischemic stroke, and death than the control group. Compared to the control group, the hazard ratios (95% confidence intervals) of the incidence of

myocardial infarction,	1.14
stroke	1.12
death	1.40

in the supplementation group after adjusting for confounding variables.
Considering the associated cardiovascular risk, calcium supplementation for osteoporosis treatment should be administered cautiously.
Download the PDF from VitaminDWiki

PubMed 2,324 articles on calcium (absorption OR bioavailability) - Oct 2024

An Algorithm to Assess Calcium Bioavailability from Foods Dec 2023 doi: 10.1016/j.tjnut.2023.12.005 FREE PDF
High Solubility and Bioavailability of Lobster Shell-Derived Calcium for Significantly Proliferating Bone and Skin Cells In Vitro - June 2023 5.9 X more bioavailable FREE PDF
Dietary and pharmacological compounds altering intestinal calcium absorption in humans and animals Dec 2015
A comparative study of calcium absorption following a single serving administration of calcium carbonate powder versus calcium citrate tablets in healthy premenopausal women. April 2014
Carbonate (4.25) slightly more than Citrate 4.16 Download the PDF from VitaminDWiki
Molecular aspects of intestinal calcium absorption June 2015
Download the PDF from VitaminDWiki
Has chart of Calcium absorption and Hormones

Calcium is mainly absorbed in the ilium, vitamin D helps – Aug 2022

Vitamin D-Mediated Regulation of Intestinal Calcium Absorption
Nutrients. 2022 Aug 16;14(16):3351.doi: 10.3390/nu14163351.
James C Fleet 1

Vitamin D is a critical regulator of calcium and bone homeostasis. While vitamin D has multiple effects on bone and calcium metabolism, the regulation of intestinal calcium (Ca) absorption efficiency is a critical function for vitamin D. This is necessary for optimal bone mineralization during growth, the protection of bone in adults, and the prevention of osteoporosis. Intestinal Ca absorption is regulated by 1,25 dihydroxyvitamin D (1,25(OH)2 D), a hormone that activates gene transcription following binding to the intestinal vitamin D receptor (VDR). When dietary Ca intake is low, Ca absorption follows a vitamin-D-regulated, saturable pathway, but when dietary Ca intake is high, Ca absorption is predominately through a paracellular diffusion pathway. Deletion of genes that mediate vitamin D action (i.e., VDR) or production (CYP27B1) eliminates basal Ca absorption and prevents the adaptation of mice to low-Ca diets. Various physiologic or disease states modify vitamin-D-regulated intestinal absorption of Ca (enhanced during late pregnancy, reduced due to menopause and aging).
Download the PDF from VitaminDWiki
--

Clipped from WikiPedia March 2011

Calcium supplements are used to prevent and to treat calcium deficiencies. Most experts recommend that supplements be taken with food and that no more than 600 mg should be taken at a time because the percent of calcium absorbed decreases as the amount of calcium in the supplement increases.[18]
It is recommended to spread doses throughout the day.
Recommended daily calcium intake for adults ranges from 1000 to 1500 mg.
It is recommended to take supplements with food to aid in absorption.

Vitamin D is added to some calcium supplements.
Proper vitamin D status is important because vitamin D is converted to a hormone in the body which then induces the synthesis of intestinal proteins responsible for calcium absorption.[29]

The absorption of calcium from most food and commonly used dietary supplements __is very similar.[30] (Present Knowledge in Nutrition)

This is contrary to what many calcium supplement manufacturers claim in their promotional materials.__

Milk is an excellent source of dietary calcium for those whose bodies tolerate it
because it has a high concentration of calcium and the calcium in milk is excellently absorbed.[30]
Soymilk and other vegetable milks are usually sold with calcium added so that their calcium concentration is as high as in milk
Also different kind of juices boosted with calcium are widely available.
Calcium carbonate is the most common and least expensive calcium supplement. It should be taken with food. It depends on low pH levels for proper absorption in the intestine.[31] Some studies suggest that the absorption of calcium from calcium carbonate is similar to the absorption of calcium from milk.[32][33] While most people digest calcium carbonate very well, some might develop gastrointestinal discomfort or gas. Taking magnesium with it can help to avoid constipation. Calcium carbonate is 40% elemental calcium. 1000 mg will provide 400 mg of calcium. However, supplement labels will usually indicate how much calcium is present in each serving, not how much calcium carbonate is present.
Antacids frequently contain calcium carbonate, and are a commonly used, inexpensive calcium supplement
Coral calcium is a salt of calcium derived from fossilized coral reefs. Coral calcium is composed of calcium carbonate and trace minerals.
Calcium citrate can be taken without food and is the supplement of choice for individuals with achlorhydria or who are taking histamine-2 blockers or proton-pump inhibitors.[34]
It is more easily digested and absorbed than calcium carbonate if taken on an empty stomach and less likely to cause constipation and gas than calcium carbonate.
It also has a lower risk of contributing to the formation of kidney stones.
Calcium citrate is about 21% elemental calcium. 1000 mg will provide 210 mg of calcium.
It is more expensive than calcium carbonate and more of it must be taken to get the same amount of calcium.
Calcium phosphate costs more than calcium carbonate, but less than calcium citrate.
It is easily absorbed and is less likely to cause constipation and gas than either.
Calcium lactate has similar absorption as calcium carbonate,[35] but is more expensive.
Calcium lactate and calcium gluconate are less concentrated forms of calcium and are not practical oral supplements.[34]
Calcium chelates are synthetic calcium compounds, with calcium bound to an organic molecule, such as malate, aspartate, or fumarate.
These forms of calcium may be better absorbed on an empty stomach.
However, in general they are absorbed similarly to calcium carbonate and other common calcium supplements when taken with food.[36]
The 'chelate' mimics the action that natural food performs by keeping the calcium soluble in the intestine.
Thus, on an empty stomach, in some individuals, chelates might theoretically be absorbed better.
Microcrystalline hydroxyapatite (MH) is marketed as a calcium supplement, and has in some randomized trials been found to be more effective than calcium carbonate.

Global Healing Center

Calcium Carbonate - cheapest and worst available
Calcium Citrate - somewhat better than Carbonate, not as good as CCM. Not need as much stomach acid
Oyster Shell Calcium
Calcium Gluconate
Calcium Lactate
Calcium Phosphate
Calcium Citrate Malate
Calcium Orotate

Good up-to-date overview from Arizona Jan 2011

Clip – – – –
Calcium Phosphate, Calcium Lactate, and Calcium Gluconate have very small percentages of elemental calcium in each supplement tablet.
Therefore it is necessary to take a large number of tablets to consume an adequate amount of calcium every day.

Calcium Citrate 21% element
Best absorbed supplemental form of calcium.It does not require the presence of extra stomach acid to dissolve.
Calcium citrate can come in colloidal form.This is a liquid form of calcium that may be less irritating to the intestinal wall.

Calcium Carbonate 40% element
Most common type of calcium supplement on the market.
Usually requires extra stomach acid for digestion, so should be taken with a meal.
Note: Seniors have less stomach acidity

GoodnessDirect March 2009 or 2004?

The inorganic forms:

Calcium sulfate
Calcium phosphate
Calcium carbonate 5-10% absorbed

The organic forms:

Calcium gluconate
Calcium lactate
Calcium citrate 30 to 35%, absorbed
Calcium amino acid chelates 65-80% absorption
Calcium orotate 90-95% absorbed, but expensive
Calcium aspartate
Calcium ascorbate

Algaecal is a much better form of Calcium to fight Osteoporosis - video May 2024

Dr. Doug 16 minutes
Dr. Doug 35 minutes long list of references

VitaminDWiki Calcium pages with CANCER in title (7 as of Aug 2022)

This list is automatically updated

Items found: 8

Title		Modified
Calcium often reduces the risk of health problems such as Colorectal Cancer – March 2024		10 Mar, 2024
Colorectal Cancer risk increases 1.6 X if high Calcium, low Magnesium and a poor gene – Sept 2007		18 Jun, 2018
Prostate cancer risk increase with Vitamin D (other studies disagree) – meta-analysis Jan 2018		11 Jan, 2018
Thyroid Cancer rate has increased 3X in 3 decades, Vitamin D Receptor decreases, Calcium increases – Aug 2017		26 Aug, 2017
Aggressive Prostate Cancer in blacks with low vitamin D – 7X more likely if added Calcium – Jan 2017		28 Dec, 2016
Cancer risk in older women reduced 32 percent by 2,000 IU of Vitamin D plus Calcium – 4 year RCT Oct 2016		12 Oct, 2016
600 mg of Calcium and a gene increases probability of Prostate Cancer by 50 pcnt – Nov 2012		07 Jul, 2013
Calcium and vitamin D appear to be among the few ways to prevent ovarian cancer – 2010		28 May, 2013