Since different forms of minerals have different levels of absorption and bioavailability, I was wondering if we could consolidate info for different forms of nutrients, especially minerals. I’ll start off with what I have now and expand it as I find more. Perhaps others can add to it.
Edit 1: Added selenium and potassium
Edit 2: Added info about iron, potassium and chromium
Calcium: Probably Calcium Citrate Malate or Calcium Citrate
Calcium Citrate and Citrate Malate have higher solubility, but this study suggests that there is little difference in absorption of different calcium forms (it’s more about what you take with it): "(1) even under controlled, chemically defined conditions, solubility of a source has very little influence on its absorbability; and (2) absorbability of calcium from food sources is determined mainly by other food components."
But, relevant for people consuming soylent, The National Institutes of Health (NIH) says: "Due to its dependence on stomach acid for absorption, calcium carbonate is absorbed most efficiently when taken with food, whereas calcium citrate is absorbed equally well when taken with or without food."
Also relevant, this study says, “The versatile nature of CCM [Calcium Citrate Malate] makes it a convenient and practical calcium salt for use in moist foods and beverages.”
Chromium: perhaps Chromium picolinate
The NIH writes: "Chromium supplements are available as chromium chloride, chromium nicotinate, chromium picolinate, high-chromium yeast, and chromium citrate. Chromium chloride in particular appears to have poor bioavailability. However, given the limited data on chromium absorption in humans, it is not clear which forms are best to take."
Anyvitamins.com write, “Chromium picolinate in this form is the most bio-available. Avoid chromium chloride, which is found in some supplements. It is mostly un-absorbable,” though it doesn’t cite any sources.
Sherry Yaft, a pharmacist, also says: "chromium picolinate is better absorbed than other forms."
The Linus Pauling Iinstitute (LPI) writes: "Chromium nicotinate and chromium picolinate may be more bioavailable than chromium chloride (17)… However, some concerns have been raised over the long-term safety of chromium picolinate supplementation."
The LPI cautions: "Most of the concerns regarding the long-term safety of chromium (III) supplementation arise from several studies in cell culture, suggesting chromium (III), especially in the form of chromium picolinate, may increase DNA damage. Presently, there is no evidence that chromium (III) increases DNA damage in living organisms, and a study in ten women taking 400 mcg/day of chromium as chromium picolinate found no evidence of increased oxidative damage to DNA as measured by antibodies to an oxidized DNA base. Several studies have demonstrated the safety of daily doses of up to 1,000 mcg of chromium for several months. However, there have been a few isolated reports of serious adverse reactions to chromium picolinate."
Note that the RDA for Chromium is 35mcg, and the examples of serious adverse reactions they cite are of people taking 600-2400 mcg/day.
Iodine: Potassium Iodide
According to NIH iodide salts, such as sodium iodide, are preferable, particularly potassium iodide: “A small study found that potassium iodide is almost completely (96.4%) absorbed in humans”
Iron: Ferrous salts or heme iron
NIH states: "Supplemental iron is available in two forms: ferrous and ferric. Ferrous iron salts (ferrous fumarate, ferrous sulfate, and ferrous gluconate) are the best absorbed forms of iron supplements."
They also write: "There are two forms of dietary iron: heme and nonheme. . . . Heme iron is found in animal foods that originally contained hemoglobin. . . . Heme iron is absorbed better than nonheme iron."
Wikipedia says of Heme iron polypeptide (HIP) (e.g. Proferrin ES and Proferrin Forte): "A clinical study demonstrated that HIP increased serum iron levels 23 times greater than ferrous fumarate on a milligram-per-milligram basis."
Heme iron, derived from animal sources, is not vegetarian, and, after shopping around, it looks like heme iron supplements are hard to find and expensive.
Magnesium: Magnesium Chloride, Lactate or Citrate
According to the NIH: "In a study that compared four forms of magnesium preparations, results suggested lower bioavailability of magnesium oxide, with significantly higher and equal absorption and bioavailability of magnesium chloride and magnesium lactate."
This study concludes: “magnesium citrate was more soluble and bioavailable than magnesium oxide.”
Molybdenum: Molybdate forms such as sodium & ammonium molybdate
The International Molybdenum Association (IMOA) cites a study which reports: “The gastrointestinal tract readily absorbs soluble, but not insoluble, molybdenum compounds [Wester et al., 1971]” A number of other studies it cites report similar findings.
One study they cite reports: "Intestinal absorption of Mo supplied as an aqueous solution is almost complete (>90%, Mo < 5 mg)."
Wikipedia writes: "Most molybdenum compounds have low solubility in water, but the molybdate ion MoO4 is soluble."
Diet.com reports: "Molybdenum in nutritional supplements is available in the form of sodium molybdate or ammonium molybdate… The efficiency of absorption of nutritional molybdenum in supplements ranges from 88-93%, and the efficiency of absorption of molybdenum from foods ranges from 57-88%."
It’s probably due to this higher absorption that the Institute of Medicine states: “More soluble forms of molybdenum have greater toxicity than insoluble or less soluble forms”(p 359).
In short if you’re using molybdenum supplements it’s advisable to stick close to the RDA (45 mcg for adults).
Kirkman Labs, a supplement maker, reports: "The only safe forms of molybdenum are molybdenum chelate, sodium molybdate, molybdenum yeast and ammonium molybdate."
I couldn’t find info on absorption of molybdenum picolinate or citrate.
According to Elson M. Haas at Healthy.net: "Potassium is well absorbed from the small intestine, with about 90 percent absorption."
Because of its high rate of absorption Livstrong.com writes: “The best form of potassium for absorption isn’t really relevant.”
The NIH writes: "The human body absorbs more than 90% of selenomethionine but only about 50% of selenium from selenite."
It cites this research, which says: "Current evidence favors selenomethionine over the other forms of selenium."
This article also states: “selenium as selenate or selenite appears to be very well absorbed but less well retained in the body than organic forms of selenium, such as selenomethionine and selenocysteine”
Zinc: perhaps Zinc Monomethionine
According to UMM: "More easily absorbed forms of zinc are zinc picolinate, zinc citrate, zinc acetate, zinc glycerate, and zinc monomethionine."
According to the LPI: "Zinc picolinate has been promoted as a more absorbable form of zinc, but there are few data to support this idea in humans. Limited work in animals suggests that increased intestinal absorption of zinc picolinate may be offset by increased elimination."
According to the NIH: "Research has not determined whether differences exist among forms of zinc in absorption, bioavailability, or tolerability."
According to this site: "Human and animal studies have demonstrated that zinc monomethionine is absorbed better, retained longer and is more effective than other zinc supplements tested."
According to Douglas Labs, a supplement producer: "Human and animal studies show that zinc monomethionine, as supplied by OptiZinc, is absorbed better than many other forms of zinc."
Douglas Labs cites this study, which showed that Zinc Monomethionine was absorbed better than Zinc Sulfate and Zince Oxide in chickens.