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Too much cholesterol in the blood “has long been considered to act as [a] primary risk factor for developing Alzheimer’s disease and, possibly, Parkinson’s disease.” I’ve shown these striking images of what the brain arteries of Alzheimer’s victims look like on autopsy, clogged with fat and cholesterol, compared to non-demented elderly controls. But wait a second: “cholesterol cannot be directly exported across the blood-brain barrier.” So, it can’t directly get into the brain, or out of the brain. What if the brain has too much cholesterol, and needs to get rid of some? As a safety valve, there’s an enzyme in the brain that oxidizes the cholesterol. And, in this form, it can exit the brain, and eventually the body. Ah, but here’s the kicker. “Although this fact means that the brain can eliminate excess amounts of these oxidation products,” it could be a two-way street. It can “allow toxic amounts of oxysterols [oxidized cholesterol] present in the blood stream” to go the other way, and “accumulate in the brain.”

This is not just a theoretical concern. This elegant study showed that by measuring oxidized cholesterol levels in the blood coming off the brain, measured in the jugular vein in the neck, compared to the levels going into the brain through the artery, you could measure the difference. And, this shows if you have too much oxidized cholesterol in your bloodstream, it can end up in your brain. This is a problem, because “the accumulation of oxysterols [can be] cytotoxic, mutagenic, atherogenic, and possibl[y] carcinogenic”—in other words, toxic to cells, toxic to DNA, and contributing to heart disease and maybe cancer. Yes, samples from atherosclerotic plaques on autopsy contain 20 times more cholesterol than normal arteries, but they contain 45 times higher levels of oxidized cholesterol.

Cholesterol oxidation products may be up to 100 times more pathological, more toxic than un-oxidized cholesterol—contributing to not only heart disease, but potentially a variety of different major chronic diseases, including Alzheimer’s. Okay, so how can we cut down on the amount of these oxysterols in our body? One way is by not eating them.

Oxidized cholesterol is found in “milk powders, meat and meat products (including fish), cheese, and eggs and egg products.”

Until recently, our understanding had been limited by the lack of testing methods to accurately analyze the amount found in various foods…until, now. Oxidized cholesterol, found throughout animal products. Canned tuna was surprisingly high, but ghee takes the cake.

Ghee, clarified butter, boiled butter, is commonly used in Indian cooking. The method of preparation appears to multiply oxidized cholesterol levels tenfold. This dietary exposure from oxidized cholesterol may help explain why the subcontinent of India is ravaged by such heart disease, even though a significant proportion of the population stays away from meat and eggs. (A number of Indian dairy-based desserts are also made in a similar way.)

Oxidized cholesterol in the diet is a source of oxidized cholesterol in the human bloodstream, where it can then readily cross the blood-brain barrier into the brain. And this could trigger inflammation inside the brain—the buildup of amyloid—all occurring “years before the impairment of memory is diagnosed.” These early studies, showing the buildup of oxidized cholesterol in the blood of those fed meals rich in oxidized cholesterol, where you get this spike in your bloodstream a few hours after you eat, were done with things like powdered egg, which can be found in a lot of processed foods. But, you typically don’t sit down to a meal of it. You get the same thing, though, from eating normal food sources. Give folks some salami and parmesan cheese, which are naturally rich in cholesterol oxidation products, and later that day, it’s circulating throughout their bodies.

And, higher levels are not only associated with mild cognitive impairment, but Alzheimer’s disease as well. “Increased…concentrations in the brain may promote cellular damage, caus[e nerve cell] dysfunction and degeneration, and could contribute to neuroinflammation” (brain inflammation) and the formation of these amyloid plaques. You can show the boost in inflammatory gene expression right in a petri dish. You can grow human nerve cells in vitro and drip a little cholesterol on, and you get a bump in inflammation. But, add the same amount of oxidized cholesterol, and it gets much worse. And, if you look at the changes in brain oxysterols at different stages of Alzheimer’s disease on autopsy, you can see how the three main cholesterol oxidation products appear to be building up. Levels have been shown to dramatically increase in Alzheimer’s-disease brains, adding to the evidence that “oxidized cholesterol [may be] a driving force behind the development of Alzheimer’s disease.”

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