I got asked in Sci. Med. Nutrition about vitamin C and oxalate production( toxic, kidney stone formation?).  I decided to post my answer here as well  because of the recent question about kidney stones.  Not long after I got  into Sci. Med. I got flamed by a medical fellow for stating that magnesium  would prevent kidney stone formation.  I'm going to state it again here. But the best way to prevent kidney stones from forming is to take B6  supplements.  Read on to find out why(I have my asbestos suit on now guys).  Vitamin C will form oxalic acid.  But large doses are needed (above 6 grams  per day).  	1. Review Article "Nutritional factors in calcium containing kidney  	   stones with particular emphasis on Vitamin C" Int. Clin. Nutr. Rev. 	   5(3):110-129(1985).  But glycine also forms oxalic acid(D-amino acid oxidases).  For both  glycine and vitamin C, one of the best ways to drastically reduce this  production is not to cut back on dietary intake of vitamin C or glycine,  but to increase your intake of vitamin B6.  	2. "Control of hyperoxaluria with large doses of pyridoxine in  	    patients with kidney stones" Int. Urol. Nephrol. 20(4):353-59(1988) 	    200 to 500 mg of B6 each day significasntly decreased the urinary  	    excretion of oxalate over the 18 month treatment program.  	3. The action of pyridoxine in primary hyperoxaluria" Clin. Sci. 38 	   :277-86(1970).  Patients receiving at least 150mg B6 each day  	   showed a significant reduction in urinary oxalate levels.  For gylcine, this effect is due to increased transaminase activity(B6 is  required for transaminase activity) which makes less glycine available for  oxidative deamination(D-amino acid oxidases).  For vitamin C, the effect is  quite different.  There are different pathways for vitamin C catabolism.   The pathway that leads to oxalic acid formation will usually have 17 to 40%  of the ingested dose going into oxalic acid.  But this is highly variable  and the vitamin C review article pointed out that unless the dose gets upto  6 grams per day, not too much vitamin C gets catabolized to form oxalic  acid.  At very high doses of vitamin C(above 10 grams per day), more of the  extra vitamin C (more than 40% conversion) can end up as oxalic acid.  In a  very early study on vitamin C and oxalic production(Proc. Soc. Exp. Biol.  Med. 85:190-92(1954), intakes of 2 grams per day up to 9 grams per day  increased the average oxalic acid excretion from 38mg per day up to 178mg  per day.  Until 8 grams per day was reached, the average excreted was  increased by only 3 to 12mg per day(2 gram dose, 4 gram dose, 8 gram dose  and 9gram dose). 8 grams jumped it to 45mg over the average excretion  before supplementation and 9 grams jumped it to 150 mg over the average  before supplementation.  B6 is required by more enzymes than any other vitamin in the body.  There  are probably some enzymes that require vitamin B6 that we don't know about  yet.  Vitamin C catabolism is still not completely understood but the  speculation is that this other pathway that does not form oxalic acid must  have an enzyme in it that requires B6.  Differences in B6 levels could then  explain the very variable production of oxalic acid from a vitamin C  challenge(this is not the preferred route of catabolism).  Increasing your  intake of B6 would then result in less oxalic acid being formmed if you  take vitamin C supplements.  Since the typical American diet is deficient  in B6, some researchers believe that the main cause of calcium-oxalate  kidney stones is B6 deficiency(especially since so little oxalic acid gets  absorbed from the gut).  Diets providing 0 to 130mg of oxalic acid per day  showed absolutely no change in urinary excretion of oxalate(Urol Int.35:309 -15,1980).  If 400mg was present each day, there was a significant increase  in urinary oxalate excretion.  	Here are the high oxalate foods:  	1. Beans, coca, instant coffee, parsley, rhubarb, spinach and tea. 	   Contain at least 25mg/100grams  	2. Beet tops, carrots, celery, chocolate, cumber, grapefruit, kale,  	   peanuts, pepper, sweet potatoe. 	   Contain 10 to 25 mg/100grams.  If the threshold is 130mg per day, you can see that you really have a lot  of latitude in food selection.  A recent N.Eng.J. Med. article also points  out that one good way to prevent kidney stone formation is to increase your  intake of calcium which will prevent most of the dietary oxalate from being  absorbed at all.  If you also increase your intake of B6, you shouldn't  have to worry about kidney stones at all. The RDA for B6 is 2mg per day for  males and 1.6mg per day for females(directly related to protein intake). B6 can be toxic(nerve damage) if it is consumed in doses of 500mg or more  per day for an extended peroid(weeks to months).    The USDA food survey done in 1986 had an average intake of 1.87 mg per day  for males and 1.16mg per day for females living in the U.S.  Coupled with  this low intake was a high protein diet(which greatly increases the B6  requirement), as well as the presence of some of the 40 different drugs that  either block B6 absorption, are metabolic antagonists of B6, or promote B6  excretion in the urine.  Common ones are: birth control pills, alcohol, isoniazid, penicillamine, and corticosteroids.  I tell my students to  supplement all their patients that are going to get any of the drugs that  increase the B6 requirement.  The dose recommended for patients taking  birth control pills is 10-15mg per day and this should work for most of the  other drugs that increase the B6 requirement(this would be on top of your  dietary intake of B6).  Any patient that has a history of kidney stone  formation should be given B6 supplements.  One other good way to prevent kidney stone formation is to make sure your  Ca/Mg dietary ratio is 2/1.  Magnesium-oxalate is much more soluble than is  calcium-oxalate.  	4. "The magnesium:calcium ratio in the concentrated urines of  patients with calcium oxalate calculi"Invest. Urol 10:147(1972)  	5. "Effect of magnesium citrate and magnesium oxide on the  crystallization of calcium in urine: changes producted by food-magnesium  interaction"J. Urol. 143(2):248-51(1990).  	6.Review Article, "Magnesium in the physiopathology and treatment  of renal calcium stones" J. Presse Med. 161(1):25-27(1987).  There are actually about three times as many articles published in the  medical literature on the role of magnesium in preventing kidney stone  formation than there are for B6.  I thought that I was being pretty safe in  stating that magnesium would prevent kidney stone formation in an earlier  post in this news group but good old John A. in Mass. jumped all over me. I  guess that he doesn't read the medical literature.  Oh well, since kidney  stones can be a real pain and a lot of people suffer from them, I thought  I'd tell you how you can avoid the pain and stay out of the doctor's office.  Martin Banschbach, Ph.D. Professor of Biochemistry and Chairman Department of Biochemistry and Microbiology OSU College of Osteopathic Medicine 1111 W. 17th Street Tulsa, Ok. 74107