<<Disclaimer: Verify this information before applying it to your situation.>>

A list of claims regarding oxalates. Myth or reality?

Claim: Oxalate prevents absorption of calcium.

The following info was taken from 
http://nutrition.about.com/

Question: Is it true that that the oxalates in tea/milk or 
chocolate/milk interfere with the absorption of calcium 
from milk?

Answer: Yes, the oxalates in tea will interfere with the 
calcium absorption from the milk. The oxalate in the tea 
binds to calcium and is removed through the digestive 
tract and not absorbed. Chocolate also contains oxalic 
acid which will bind up some calcium. A cup of tea may 
only have a small amount of milk added, so the tea may 
bind up a fair amount of the calcium, but a glass of 
chocolate milk would contain a lot more calcium than 
oxalate and would still be a good source of calcium.

Sources:

Charrier MJS, Savage GP, Vanhanen, L. "Oxalate content and 
calcium binding capacity of tea and herbal teas." Asia 
Pacific Journal of Clinical Nutrition 11 (4), 298-301.

Brinkley L, McGuire J, Gregory J, Pak CY. "Bioavailability 
of oxalate in foods." Urology. 1981 Jun;17(6):534-8.

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Claim: Oxalate is a poison.

The following information taken from Professor Nancy 
Lowry, Hampshire College, Amherst MA 
(http://helios.hampshire.edu/~nlNS/mompdfs/oxalicacid.pdf)

As poisons go, oxalic acid is not lethal in teeny 
quantities like those from poison darts frogs. The LD50 
orally in rats is reported as 375 mg/kg; the Merck Index 
reports the LD for dogs as 1 g/kg.

We can only make guesses about the poisonous doses for 
people. Using the LD50 figure for rats, a 130 pound (58.9 
kg) woman would need to consume about 22 grams of oxalic 
acid to be in serious danger of death.

Rhubarb leaves contain 0.5-1.0% oxalic acid, so that you 
would need to eat quite a large serving of the sour leaves 
(perhaps 10 pounds) to get a lethal dose. However, a 
fraction of that could nevertheless cause severe symptoms 
of oxalic acid poisoning.

One neat quote I came across: “A few leaves won't hurt a 
horse, a wheelbarrow full can kill pigs.”

One often repeated story features the English government 
in World War I. It sent out an advisory encouraging its 
citizens to eat rhubarb leaves to alleviate food shortages 
and help the war effort. After sicknesses and deaths were 
reported, the recommendation was rescinded.

Calcium binds very strongly to the oxalate anion, forming 
calcium oxalate, which is extremely insoluble in water. 
Because of the strength of the calcium/oxalate pair foods 
rich in both calcium and oxalate are pretty useless as a 
source of calcium. In addition, cooking does not wash out 
oxalate from sources that are high in oxalate and calcium, 
although it does help in foods that are high in potassium 
oxalate like skunk cabbage. [That goes for iron also, so 
spinach is not a good source of iron (Popeye to the 
contrary) because the iron is tightly bound to oxalate and 
therefore not available for the body’s use.]

Table I: Oxalic acid content in selected vegetables.

These are ballpark numbers, actual content depends on many 
variables.
See note ate the end of the article.

Vegetable - Oxalic acid (g/100 g)
Asparagus - 0.13
Broccoli - 0.19
Lettuce - 0.33
Brussels sprouts - 0.36
Collards - 0.45
Beet leaves - 0.61
Spinach - 0.97 (0.32-1.26)
Purslane - 1.31
Parsley - 1.70

Selected References:

Amounts of oxalic acid in various foods:
USDA: Oxalic Acid Content of Selected Vegetables:
http://www.nal.usda.gov/fnic/foodcomp/Data/Other/oxalic.html

Food Science, Lincoln University, NZ: Oxalate Containing 
Foods
http://www.foodscience.ac.nz/research_topics/oxalate/Oxalate_containing_food.html

Mallinckrodt Baker, Inc. MSDS. Fatal dose figure for 
oxalic acid:
http://www.jtbaker.com/msds/englishhtml/o6044.htm

Shooting crystals:
Dr. T. Ombrello, Union County College: Plant of the Week: 
Dumbcane
http://faculty.ucc.edu/biology-ombrello/POW/dumbcane.htm

Dr. T. Ombrello, Union County College
http://www.cook.rutgers.edu/~floriculture/publications/dumbc.htm

Mary C. Smith, DVM: Oxalate Poisoning: Horse and pig quote
http://www.maltawildplants.com/OXIL/Docs/Oxalate%20Poisoning.htm

LD50 figures can seem to be wildly different as well as 
notoriously difficult to extend to people. The calculation 
of the lethal amount of rhubarb leaves above was based on 
an LD50 orally in rats of 375 mg/kg and calculates to a 
fatal dose of oxalic acid of about 22 grams of oxalic 
acid.. However, another MSDS estimates that the fatal dose 
would be about 5 to 15 grams. In addition, the amount of 
oxalic acid in a blade of rhubarb is not a fixed number, 
but depends on leaf size, soil, developmental stage at the 
time of picking, the particular species of rhubarb, and 
more. Clearly, this is not an exact but complicated 
science!

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Claim: Oxalate causes vulvodynia.

In early 2006, there were two articles on the PubMed 
database that involved research into oxalates and 
vulvodynia.  The first article from 1991 (PMID:1816400:) 
was a case report of a woman that had suffered from 
vulvodynia for 4 years, and the condition had become 
debilitating.  A series of tests showed that the 
alkalinity and oxalate level of her urine often rose to 
abnormal levels, and her discomfort was linked to these 
surges in oxalates. The woman was put on a program to 
control oxalates that included a calcium citrate 
supplement. The woman improved significantly by a 3 month 
follow up, and was symptom free after a year on calcium 
citrate. When the woman stopped taking calcium citrate, 
her symptoms would return; when she restarted the 
supplement, her vulvodynia went into remission.  So in one 
case, a strong relationship between oxalates and vulvular 
pain was demonstrated.

A second study was conducted in 1997 that included 130 
women with vulvular pain syndrome (PMID:9322615).  Lab 
tests showed that just under half of the women (59 
patients) had elevated oxalate levels.  These 59 were put 
on a program that included a low oxalate diet and calcium 
citrate. The results of this study were less dramatic than 
in the first case study: 24% (14 patients) demonstrated an 
'objective improvement' and 10% (6 patients) improved to 
the point of being able to have normal sexual intercourse. 
 The researchers concluded that oxalates might aggravate 
vulvodynia, but was not the cause for most women in the 
study.

 From the limited research (and from anecdotal information 
on the web), it can be said that a program to reduce 
oxalates in the diet along with a supplement of calcium 
citrate might provide a measure of relief to some women 
with vulvodynia.

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An interesting perspective:

Having excess oxalates in your body (whatever the reason) 
is somewhat analogous to having diabetes. Eating sugar 
doesn't cause diabetes, and eating foods high in oxalate 
doesn’t cause the symptoms and conditions associated with 
high oxalate levels. However, cutting sugar/carbohydrates 
out of your diet is part of the treatment for diabetes. 
Likewise, the low oxalate diet is part of an overall 
dietary regimen to prevent things like kidney stones, 
interstitial cystitis, fibromyalgia, vulvodynia, or 
connective tissue disorders in general.

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