Summary
Dry Milk contains higher levels of some chemicals than regular milk (but lower than, say, eggs). There is some evidence that these chemicals may cause heart disease, although the link is not clearly established.
Definitions
Some definitions, which might be useful later:
Oxysterols in Dry Milk
The Wikipedia page on Dry Milk reports:
Commercial milk powders are reported to contain oxysterols (oxidized
cholesterol) in higher amounts than in fresh milk (up to 30 μg/g,
versus trace amounts in fresh milk). Oxysterols are derivatives of
cholesterol that are produced either by free radicals or by enzymes.
Certain free radicals-derived oxysterols have been suspected of being
initiators of atherosclerotic plaques. For comparison, powdered eggs
contain even more oxysterols, up to 200 μg/g.
To support the oxysterol levels, it references:
- "Advanced Dairy Chemistry: Volume 2 - Lipids" by P.F. Fox and P. McSweeney, Birkhäuser, 2006 ISBN 978-0-387-26364-9
To support the idea that dry-milk-based oxysterols are dangerous, they cite:
The abstract of this paper makes only weak claims of suspected/possible danger:
Cholesterol under certain in vitro and possibly in vivo conditions may be oxidized to oxysterols, which are suspected of being initiators of atherosclerotic plaques. Oxysterols inhibit HMG-CoA reductase activity resulting in a decreased cholesterol concentration in the cell membrane, which leads to endothelial membrane injury and probable premature cell death. Exogenous oxidation of cholesterol in human tissues under certain unusual conditions is highly probable. Dietary oxysterols are absorbed in the gastrointestinal tract and are selectively transported by the athrogenic lipoproteins LDL and VLDL. The oxysterols cholestanetriol and 25-OH cholesterol have been shown to be atherogenic. Oxysterols are commonly found in dried egg products, powdered milk, cheeses and in a variety of high temperature dried animal products.
Searching further, I found:
- Klaus Zorn-Pauly, Peter Schaffer, Brigitte Pelzmann, Eva Bernhart, Guofeng Wei, Petra Lang, Gerhard Ledinski, Joachim Greilberger, Bernd Koidl, Gunther Jurgens, Oxidized LDL induces ventricular myocyte damage and abnormal
electrical activity—role of lipid hydroperoxides Cardiovasc Res (2005) 66 (1): 74-83.
doi: 10.1016/j.cardiores.2004.12.009
They showed that guinea-pig cells, in a dish, dosed with Ox-LDL:
induced cell damage and irregular electrical activity in ventricular myocytes. [...] The observed
effects may play a role for functional cardiac abnormalities in patients with increased ox-LDL levels.
Another source cast further doubts:
According to current concepts, oxysterols are physiological
mediators in connection with a number of cholesterol-induced metabolic effects. However, most of the evidence for this
is still indirect, and there is a discrepancy between the documented potent effects of oxysterols under in vitro conditions
and the studies demonstrating that they are of physiological importance in vivo. [...] The present review is a critical evaluation of the literature on oxysterols, in particular, the in vivo evidence for a role of oxysterols as physiological regulators of cholesterol homeostasis and as atherogenic factors
[...]
As judged from the results of animal experiments, the normal
dietary intake of oxysterols is probably of little or no importance
in the development of atherosclerosis.
In 2003, a Chilean paper repeated (but did not test) the claims that milk powder contains oxidized cholesterol, and that it is potentially harmful.
Several dairy products and milk powder are reported to contain
oxidized cholesterol after processing (Dionisi et al., 1998). The
oxysterols found in these products are the same as those in processed
eggs. However, fresh milk contains 0 or only trace amounts of
cholesterol oxides, which means that processing (e.g high temperature)
is the main source of oxysterols (Angulo et al., 1997). Other
milk-derived products such as cheeses, yogurt, and evaporated milk,
contain very low amounts of cholesterol oxides. The oxysterol content
of milk powder is in the range 1.0-2.5 ug/g. Dehydrated cheese has
8-15 ug/g; skimmed milk powder, 0.01-0.1 ug/g; and whole milk powder,
0.2-0.8 ug/g (Paniangvait et al., 1995). The amount of oxysterols present in these products depends on the processing temperature and
the length of the storage period (Nourooz-Zadeh & Appelqvist, 1988).
[...]
The cytotoxic, mutagenic and probably carcinogenic effects described for some oxysterols have been observed in in vitro models. However, the atherogenic action of oxysterols has been demonstrated in both in vitro and in vivo study models, to be the best-characterized pathological expression of cholesterol oxidation (Staprans et al., 1998; Leonarduzzi et al., 2002) and comparable to the atherogenic action of trans fatty acid isomers (Valenzuela & Morgado, 1999).
This paper supports the idea that some oxidized LDL could cause harm, based on experiments in dishes:
- G M Chisolm, G Ma, K C Irwin, L L Martin, K G Gunderson, L F Linberg, D W Morel, and P E DiCorleto, 7 beta-hydroperoxycholest-5-en-3 beta-ol, a component of human atherosclerotic lesions, is the primary cytotoxin of oxidized human low density lipoprotein, PNAS November 22, 1994 vol. 91 no. 24 11452-11456
At this link also Cole Watts have mentions of oxysterols and their possible relation to Alzheimer's disease:
Oxysterols are substances that are created as our bodies use and break
down the elements in cholesterol. We’ve all heard how it’s important
to keep our cholesterol levels down, and that our “good” cholesterol
number, or HDL, should be normal or above normal, for better health.
But it plays a more important role than that. Oxysterols that are
produced from our bodies using cholesterol are meant to be broken down
by the liver. However, people with a number of diseases like Hardened
Arteries and Multiple Sclerosis have been found to have extremely high
level of Oxysterols in their bodies. This has been found in some
patients with Alzheimer’s Disease, as well.
[...]
The reason science is taking a hard look at the link between
Oxysterols and Alzheimer’s is that our central nervous system contains
the highest concentration of cholesterol in our bodies. Our brains
need cholesterol to function properly. Many people believe that
cholesterol is simply something to be watched in the diet to avoid
heart disease and arteriosclerosis, but it’s something that’s vital
for life.
[...]
While cholesterol itself doesn’t actually cross the blood-brain
barrier, some of its by-products do. So any cholesterol-related
processes that take place will affect the brain and nervous system
heavily, most likely more than any other bodily system.
[...]
Only about a dozen of the known Oxysterols have been studied, and much
more research is needed for the many that we haven’t explored.
Scientists do say that since the Oxysterols are created when our
bodies utilize cholesterol, and that a great deal of the cholesterol
we have is produced by our bodies and not thanks to diet, a change in
diet won’t affect the levels that might be linked to Alzheimer’s and
other diseases.
Finally, this article looks at the types of Low Density Lipoproteins (LDL)and shows that Oxidized Low Density Lipoproteins (ox-LDL) causes cell damage.
Briefly: Oxysterols are produced in our body already. Dry Milk contains oxysterols in a low amount, but enough to increase the natural levels. Research on diseased bodies shown that they also contain high oxysterol levels. This shows us oxysterols might be playing a bigger role than we know and that Dry Milk ma be harmful for long term usage, but the research is not yet clear.
