Calcium, Magnesium and Iron: Understanding Mineral Supplements

Calcium, magnesium and iron come in many different forms in supplements. Here is some information to help you understand how the forms of these minerals vary, and how to determine whether your supplements are of good quality. As always, consult your naturopathic doctor or healthcare provider to determine which forms of minerals and supplements are best for your unique, individual needs.


Types of Calcium: The most absorbable and bioavailable kinds of calcium are calcium citrate and calcium citrate-malate (even better). You won't often see calcium citrate-malate in supplements found in most stores, but calcium citrate is the next best option. When bone deposition is a concern (e.g. in osteopenia or osteoporosis), hydroxyapatite is the preferred type of calcium (sometimes called MCHC). 

Calcium carbonate is a cheaper form of calcium that is found in many brands. It contains the most elemental calcium, but it is in a form that is not easily absorbed and is not highly bioavailable. 

Avoid calcium supplements that only contain calcium - these are not balanced with other important, synergistic nutrients (such as magnesium, vitamin D3 and K2). Ingesting calcium by itself increases the risk of cardiovascular disease and does not improve bone mineralization. Calcium taken by itself may be deposited in the arteries and soft tissues, rather than in the bones. Vitamin K (especially K2) “guides” the calcium to be deposited into bone preferentially rather than soft tissues and arteries. But note that vitamin K may not be appropriate for people with certain conditions. Check with your ND, MD or pharmacist to make sure vitamin K is safe for you.


There are many different forms of magnesium. Each kind differs as to absorbability and function in the body. Some supplements have a mixture of several different types of magnesium, which provides the widest spectrum of benefits. Here's a list of the most common types of magnesium found in supplements, and what they do:

  • magnesium oxide: most poorly absorbed and therefore has a strong laxative effect; inferior choice for treating deficiency or maintaining adequate levels; best choice if laxative effect is desired (short-term use only, and not be used in case of bowel obstruction).
  • magnesium citrate: rapidly absorbed but still has some laxative effect (although not as much as oxide); common and inexpensive form found in supplements. An OK choice as long as loose stools don’t become an issue.
  • magnesium glycinate / bisglycinate: absorbed even better than citrate; common form found in higher quality supplements; has a calming effect and relaxes muscles.


Iron exists as heme iron (which comes from animals) and non-heme iron (which comes from plants, so suitable for vegans). Heme iron is absorbed far better than non-heme iron (50 mg of non-heme iron = 3 mg heme iron absorbed). Most over-the-counter supplements contain non-heme iron, either as ferrous or ferric iron. Ferrous iron is much more absorbable than ferric, and comes in several different forms: ferrous-gluconate, citrate, sulfate, fumarate,  or succinate. Ferrous fumarate and ferrous succinate are absorbed the best and are the least likely to cause digestive disturbances (such as constipation). Of these, ferrous succinate is superior.


Disclaimer: Information can be empowering, but we all have unique health profiles and needs. Health-related information contained in this post is intended to be general in nature and should not be used as a substitute for a visit with a Naturopathic Doctor. The advice is intended to offer only a general basis for individuals to discuss their medical condition with their health care provider. Always consult your licensed Naturopathic Doctor or health care provider.