Calcium

Scientific studies (review articles) on the relationship between calcium and disease prevention:
One swallow does not make a summer. A famous Dutch saying that could not be any more obvious. Just because one single scientific study about a certain topic makes certain claims, it does not necessarily mean it is true. On the other hand, a review article (a collection of scientific studies on a certain topic) of randomized, placebo-controlled double blind clinical trials (RCTs) will answer the following question:
"Do taking dietary supplements make sense?" Yes for a positive conclusion and no for a negative conclusion.

One swallow does not make a summer. A famous Dutch saying that could not be any more obvious. Just because one single scientific study about a certain topic makes certain claims, it does not necessarily mean it is true. On the other hand, a review article (a collection of scientific studies on a certain topic) of (prospective) cohort studies or case-control studies will answer the following question:
"Should I change my diet?".

1. Dietary intake of 200-700 mg/day calcium reduces stroke among Asians
2. Hypocalcemia is associated with poor outcome in COVID-19 patients
3. Dairy products reduce causal fat mass and BMI among overweight or obese adults
4. 100 µg/d vitamin K2 + 1000 mg/d calcium supplements increase lumbar spine bone mineral
5. Calcium + vitamin D supplementation reduce hip fracture in postmenopausal women
6. 280 mg/d dietary calcium intake may reduce metabolic syndrome
7. 0.6-2 gram calcium supplement reduce gestational hypertension
8. Calcium intake of 750 mg per day could be a risk factor for prostate cancer
9. Post-diagnosis calcium, vitamin C, D or E decreases cancer mortality
10. Dietary calcium intake reduces colorectal adenomas
11. At least 1600 mg/day calcium may reduce the recurrence of colorectal adenomas
12. Daily 621 mg dietary calcium has protective effect against esophageal cancer in Asian populations
13. Long-term cheese consumption does not increase risk of all-cause mortality
14. Daily 700-1000 mg dietary calcium intake increases cardiovascular disease in healthy postmenopausal women
15. 200-1500 mg/d dietary calcium intakes do not increase cardiovascular disease
16. A daily dose of ≥200 g yogurt intake decreases cardiovascular disease risk

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• Calcium is one of the most important minerals for the human body.
• Calcium is found in milk and dairy products, broccoli, cabbage, kale, tofu, sardines and salmon.
• The primary function of calcium is to form the structure of bones and teeth.
  Calcium also plays important roles in nerve conduction, muscle contraction and blood clotting.
• A calcium deficiency results in skeletal abnormalities, such as osteopenia, osteomalacia, osteoporosis and rickets, insomnia, tetany, premenstrual cramps and hypertension (high blood pressure).
• High calcium intake (>2500 mg per day) may lead to constipation, an increased risk of developing calcium kidney stones and inhibition of absorption of iron and zinc from food.
• Calcium is both actively (95% by vitamin D) and passively absorbed in the small intestines.
  The absorption of dietary calcium is 25 to 60%. In individuals with gross vitamin D deficiency, only 10%-15% of dietary calcium is absorbed.
• Vegetarians may absorb less calcium than omnivores, because they consume more plant products containing oxalic and phytic acids. Oxalic and phytic acids can decrease the calcium absorption.
• With ageing, the body’s ability to absorb calcium declines, particularly from the age of 50 years onwards.
• Calcium is excreted primarily in the urine and feces, with a number of factors thought to increase urinary calcium loss, including intake of caffeine, protein and sodium (>6 gram per day), as well as low estrogen levels.
• The two main forms of calcium in supplements are carbonate and citrate.
  Calcium carbonate is the most common and least expensive form of calcium. Therefore, it is the most used form in supplementation.
  Calcium carbonate supplements provide greater amounts of elemental calcium and consequently require fewer tablets than other forms of calcium.
  Calcium citrate should be used in individuals with suspected achlorhydria, inflammatory bowel disease, or absorption disorders.
  Calcium citrate supplements should also be recommended for individuals treated with H2 blockers or proteinpump inhibitors.
  Calcium lactate and calcium gluconate are less concentrated forms of calcium.
• Calcium carbonate contains 40% elemental calcium. Thus, 500 mg of elemental calcium is equivalent to 1250 mg of calcium carbonate.
  Calcium lactate contains 13% elemental calcium, whereas calcium gluconate contains only 9% elemental calcium.
• Calcium carbonate requires an acidic environment in order to be dissolved in the intestine and absorbed into the blood. Stomach acid production increases in the presence of food, creating an acidic environment.
  Therefore, calcium carbonate supplements should be taken with a meal.
  Calcium citrate does not require the presence of stomach acid to dissolve and be absorbed and may be taken on an empty or full stomach.
• Absorption of calcium from dietary supplements is greatest when taken in a dose of 500 mg or less. Therefore, the dose of elemental calcium should not exceed 500 mg at a time and to allow four to six hours between doses.
• 1-1.5 grams of protein per kg body weight is needed to maintain a normal calcium metabolism. A normal calcium metabolism is needed for strong bones. 
• Protein is also necessary for bone formation. Bone is approximately 50% protein by volume.
  Adequate exercise (at least 30 minutes per day) is also important for normal bone formation, while immobilisation results in rapid bone loss.
  Strength training can increase bone formation.
• At least 800-1200 mg calcium per day and 800-1200 IU (20-30 mcg) of vitamin D in combination with at least 30 minutes of physical activities daily over a lifetime can help prevent osteoporosis.1 mg = 1000 mcg.
• It is important to maximize bone mass in order to reduce the risk of osteoporosis in later life. Bone mass is accrued up until the age of 30-35, when peak bone mass is achieved. From the age of about 35 years bone mineral loss exceeds bone mineral formation.
• Magnesium, zinc and fluoride are also deposited in the protein matrix of bones, although calcium is the most abundant mineral in bone.
• Hypocalcaemia is low calcium levels in the blood serum. The normal range is 2.1 to 2.6 mmol/L with levels less than 2.1 mmol/l defined as hypocalcemia.
• The total body stores for calcium are 1-1.2 kg.
  99% of all the calcium in the body is found in the bones and teeth in the form of hydroxyapatite. The remaining 1% is found in the blood.
• The tolerable upper limit intake has been set at 2500 mg calcium per day.