Xanthine Oxidase in Homogenized Milk and Cardiovascular Damage

Posted on 25 Oct 2012 01:08

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Xanthine oxidase is an enzyme in milk, found in the milk fat globules. It is a specific oxido-reductase involved in purine catabolism, catalyzing the oxidation of hypoxanthine to xanthine and of xanthine to uric acid 1,2 It's antimicrobial role is due to its ability to help generate reactive oxygen species which are highly bactericidal or bacteriostatic. It may also be that its antimicrobial effect is derived from the formed hydrogen peroxide that participate in the lactoperoxidase system.2

In 1971, a paper by Oster set forth the theory that xanthine oxidase, having been absorbed onto homogenized milk fat droplets could enter the bloodstream, when it would normally be excreted in non-homogenized milk. XO was claimed to then enter the heart and arteries and damage the membranes, causing scar tissue which allowed cholesterol to build up and thus clog the arteries.3 This theory has been enthusiastically parroted by alternative health publications in the years since, even though there was virtually no corroborating evidence to back up the claims.

The postulation that xanthine oxidase in homogenized milk does such cardiovascular damage was refuted in a 1983 paper by Clifford, et al: Homogenized bovine milk xanthine oxidase: a critique of the hypothesis relating to plasmalogen depletion and cardiovascular disease.4 The abstract follows. Please follow the link for the full paper.


A hypothesis has repeatedly been promoted that xanthine oxidase from homogenized bovine milk is absorbed intact, damaging cardiovascular tissue by depleting plasmalogens and initiating atherosclerotic changes that culminate in heart disease. In the light of recent experimental evidence, the present paper examines the validity of this hypothesis and associated claims. The evidence leads to the conclusion that 1) absorption of dietary xanthine oxidase has not been demonstrated; 2) a relationship between intakes of homogenized milk and levels of serum xanthine oxidase activity have not been established; 3) a direct role for xanthine oxidase in plasmalogen depletion has not been established; 4) neither liposome formation during homogenization of milk nor absorption of intact liposomes from the gastrointestinal tract has been demonstrated; and 5) data are lacking to support the claim that large doses of folic acid inhibit xanthine oxidase in vivo and/or are therapeutic in heart disease. Experimental evidence has failed to substantiate, and in many cases has refuted, the xanthine oxidase/plasmalogen depletion hypothesis.

Xanthine Oxidase Touted as One of the Benefits of Raw Milk

Interestingly, this same xanthine oxidase which is supposed to be so dangerous when consumed in homogenized milk, because of its different form, is seen as a great benefit in raw milk. This enzyme, which when discussed as a poison in homogenized milk, is said to be excreted untouched, but when discussed as a selling benefit for raw milk, it exerts the antimicrobial properties in the gut, along with other antimicrobial compounds naturally present in milk which include lactoferrin, lactoperoxidase, and lysozyme.

There is no evidence that any compounds in raw milk kill pathogens, and raw milk does not contain enough of these compounds to do this, even if they were able to exert such an effect in the human gut.

1. Farkye, N. Y. 2003. Other enzymes, p. 571-603. In P. F. Fox and P. L. H. McSweeney (ed.), Advanced Dairy Chemistry. Volume 1. Proteins. Part A, Kluwer Academic/Plenum Publishers, New York.
2. Harrison, R. 2006. .Milk xanthine oxidase: properties and physiological roles. International Dairy Journal. 16:546-554.
3. Oster, K. A. 1971. Plasmalogen diseases: A new concept of the etiology of the atherosclerotic process. American Journal of Clinical Research. 2:30-35.
4. Clifford, A. J., C. Y. Ho, and H. Swenerton. 1983. Homogenized bovine milk xanthine oxidase: a critique of the hypothesis relating to plasmologen depletion and cardiovascular disease. The American Journal of Clinical Nutrition. 38:327-332.

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