Calcium
TL;DR
something.
Blocks iron absorption.
Vitamin d aids/boosts absorption.
Essential mineral and electrolyte
Plus bones etc.
vit d and k thing
See: electrolytes
See: salt.
Avoid taking vitamins, minerals and other supplements for 30-60 minutes after consuming coffee - it contains compounds (polyphenols) that limit the absorption of many micronutrients.
Forms/Types
Calcium citrate can absorb well when taken with or without food. Other forms cannot.
Quality
As with all supplements - buyer beware. It's quite common for supplements to be contaminated with a variety of impurities, often in the form of heavy metals, and/or contain far more or less of the ingredients stated on the label. There's no simple rule of thumb to avoid this, such as avoiding cheap or imported products; expensive or well-known brands produced in-country may be just as bad. Ideally you should take some time to find products (if you can) that;
- have been laboratory tested on behalf of the manufacturer by a reputable body or company that operates in your country or region (here's an example of a Peak Supps creatine supplement available on Amazon in the UK which has been tested by Eurofins: Creatine Monohydrate Powder 1Kg | Pure Micronised | Packaging May Vary - see pictures 3 & 4)
- have been laboratory tested by an independent testing company that ranks product purity and ingredient amount accuracy on behalf of consumers (usually funded by affiliate sales of those products). An example of this is Labdoor.
Dosage - How Much?
Calcium is absorbed best when taken in amounts of 500 – 600 mg or less - https://www.bonehealthandosteoporosis.org/patients/treatment/calciumvitamin-d/.
Deficiency - Too Little
Known as hypocalcemia.
Toxicity - Too Much
Known as hypercalcemia.
Careful about taking too much.
2500mg or 2000mg per day for adults and those over 50 years old, respectively.