>>"Thus, magnesium citrate was more soluble and bioavailable than magnesium oxide."<<
1 for 1, this is true, however many things affect the absorption rate including the digestive health of the individual and when and with what the supplement is taken.
In addition, magnesium content in an oxide is about 60%, and in a citrate or chelate, 12 - 16%.
So while gram for gram the magnesium in a citrate or chelate form may be absorbed at a higher rate, the oxide form has more magnesium to absorb and in certain individuals, can offer more magnesium. 2 out of 6 individuals showed this in one small study.
Again this depends upon digestive health, with what, and when taken.
Another interesting aside here is that magnesium levels in blood are tightly regulated, and increased magnesium levels in urine happen with all magnesium supplements, including Epsom Salt baths or magnesium oil use...
That one has greater amounts in their urine is an indication that they are taking more than they can use at any one time...
Supplementation gets one into the sticky wicket of offsetting/imbalancing other nutrients with too much magnesium if they go overboard... such as antagonizing the balance of sodium, potassium, calcium, iron, selenium, copper, lithium, silicon / silica, manganese, to name a few, also vitamin A, B's, K, folate, vitamin D, and others.
I am convinced that food, including herbs and spices, are the absolute best way to get our nutrition as Moreless states, HOWEVER, given the current state of our foods, and our environmental, nutrition robbing pressures (read all kinds of pollution), sensible supplementation is needed in many cases.
One only need study the increasing cancer rates in wild animals, birds and fish to understand this need.
Supplementation, IMO would be best achieved with food state nutrition, which could be realized by using a small amount (the amount one may find in foods), of some form of a powdered supplement with a meal. Many tribal cultures used pinches of salts, clays, alkaline ashes, lime, and sea vegetables... In this case, to increase magnesium levels, a pinch (pinch size depending upon need) of Epsom Salts with meals in water or sprinkled on the food, would fit the bill as well as anything else... and it is readily available and cheap... even in a post supplement world if it comes to that (codex, etc.). Why do you think the pharmaceutical companies were/are buying up their competition, the supplement companies?
As a rough example of food based nutritional value; an individual with potassium deficiency; instructed by his physician that he required more potassium... he insisted on "food" sources as apposed to prescription supplementation... at least 1 Low sodium V8 per day his physician instructed and the addition of 2 other high potassium foods (he usually has bananas) a day and a tablespoonful or two of black strap molasses (about 20% RDA per tablespoonful).
About 34% RDA potassium in one can of V8... I will not get into the organic vs conventional (I wish V8 had an organic low sodium product - but one can juice their own if need be), or that the V8 has Potassium chloride added to it, but I will tell you the individual's potassium levels and blood pressure all leveled out nicely within short order - using foods, and technically, potassium chloride supplementation.
The idea here is that when taken with food, the "supplement", potassium chloride, was better absorbed and utilized.
An interesting aside here is that potassium levels influence magnesium absorption as well... as does other factors, like sodium and calcium among others.
Bottom line - Variations of a particular "single" nutrient need and the ability to absorb and utilize that nutrient is different in each individual, dependent upon several, perhaps dozens of factors.
BTW - do not get all in a bunch because I mentioned Moreless... he is right about the increased need for the smörgåsbord of alkaline minerals that are lacking, sometimes severely lacking, in our conventional and processed foods, just as silica and sulfur are lacking, however he never states that the alkaline minerals should be taken by themselves without complementary acids in a preferably carbon bound form (likely one reason for lemon or ACV and Black Strap Molasses in the drink), in order to properly, and efficiently absorb them.
I have had extremely excellent results with learning, understanding, and applying moreless's protocol (while the protocol emphasizes alkaline minerals, it also includes acids)... and I doubt I am an anomaly judging from the testimonies... whether you believe them or not is irrelevant to me... the proof is in the results I have experienced over 5+ years.
Among the results are a 50+ pound weight loss without dieting per se... I never count calories and eat all the fats, and sugars I want... the form of those fats and sugars is what matters.
Granted, I looked for and found strong foundational similarities in moreless's protocol with Schulz, Christopher, Barefoot, your own and many others on these boards... whether they understand and see the similarities with the other protocols/teachings or not has more to do with their emotional opposition to moreless that blinds them, preventing them from seeing it, than anything else.
My "miraculous" results following and studying the principles of moreless's teachings have led to a group of physicians accepting my services in giving nutrition classes to other physicians and health care professionals.
I do not introduce moreless's protocol to them, however I introduce soil science, including microorganisms, and sound nutritional advice... including things like food based supplementation if needed.
Given the occasional opportunity for 1 on 1, I get into more of the details... including that males and females and people from different racial/ethnic backgrounds have different, sometimes very different, nutritional needs.
Is what moreless teaches for everyone? No, absolutely not, anyone who doubts, questions, or believes it is a bunch of bunk, or cannot stand his posting style that insists upon accepting and exercising personal responsibility, is better off going elsewhere.