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DEAR DOCTOR: How should chocolate be processed to preserve its healthful properties? I've read that a non-alkalizing process is better than an alkalizing process, but I don't understand the difference.

DEAR READER: Ever since studies revealed that chocolate can convey health benefits, a certain segment of the population (hello, fellow chocolate lovers) has been doing a happy dance. Researchers have found that biologically active compounds in chocolate, known as flavonoids, can lower cholesterol, prevent memory decline and reduce the risk of developing heart disease. (Cocoa is also a good source of potassium, magnesium and phosphorus.) But while the headlines simplified the findings to just plain "chocolate," the facts of the matter are a bit more complex.

Chocolate is the end product of a multistep process that begins with the colorful, podlike fruit of the cacao tree. Farmers harvest the cacao pods and separate the seeds from the fleshy (one reference we read used the word "mucilaginous") white pulp via a multiweek process of fermentation and drying. The seeds are then roasted and ground into chocolate liquor, a thick liquid comprised of cocoa butter and cocoa solids. From there, it's up to each manufacturer how this liquid will be manipulated, and how much sugar and other ingredients will be added to create the final product that we call chocolate.

Which brings us back to those flavonoids. They are a class of plant nutrient contained in most fruit and vegetables. Not only do they give our fresh food those bright colors, they're also powerful antioxidants that help boost the immune system and act as anti-inflammatories. One of the subgroups of flavonoids are flavanols, which are found in grapes, apples, berries, tea, red wine and -- here's why they're important to this discussion -- cocoa. And like many micronutrients, they can be damaged during cooking or processing.

Cocoa is naturally acidic, which can give the natural products a rough edge. Natural cocoa powder is basically a cocoa bean concentrate. It's light brown, slightly fruity and has a penetrating and bitter flavor. To take the edge off that bitterness, some manufacturers treat the cocoa with an alkalizing agent. Cocoa that has been alkalized is also known as Dutch-process.

This type of processing makes the cocoa powder darker, decreases the bitterness, and makes it smell and taste more "chocolatey." However, it does have a negative effect on flavanol levels. In some analyses, cocoa that had been alkalized had half of the amount of flavanols as did natural cocoa. So, if your chocolate intake is specifically for its health effects, then natural cocoas are the way to go.

Whether alkalized or not, pure cocoa is extremely bitter. To make it palatable, chocolate products are highly processed. In addition to fermenting, roasting and alkalization, all of which can reduce flavanol levels, cocoa is combined with sugar, fat and various milk products. The result are foods whose fat and sugar levels may outweigh whatever advantages the flavanols would confer.

Bottom line? Despite its purported health benefits, chocolate is not a food group. (Sorry, chocoholics.) Instead, think of it as a condiment. Go for the darker, less processed varieties, and just enjoy a square or two at a time.

DEAR DOCTOR: I've been diagnosed with polycythemia vera, which I understand is very rare. I'm currently being treated with phlebotomies. Please explain this diagnosis and what science has learned about it.

DEAR READER: To understand polycythemia vera (PV), you must first understand how bone marrow works. For starters, the marrow is full of stem cells that eventually become red blood cells (which carry oxygen), platelets (which help the blood to clot) and white blood cells (which fight infection). Initially, however, the stem cells become either lymphoid cells (which develop into lymphocytes, a specific type of white blood cell) or myeloid cells (which develop into red blood cells, platelets or white blood cells that are not lymphocytes). PV occurs when the myeloid cells reproduce preferentially, producing more of their type of cells.

This causes a significant elevation in the number of red blood cells and, to a lesser degree, platelets and white blood cells. The origin of this proliferation is linked to a mutation in the JAK2 gene, which is only occasionally linked to a genetic susceptibility within families. More often than not, it's a random mutation.

The greatest complications of PV are due to the increased concentration of red blood cells and platelets within the blood stream. This increases the risk of blood clots, which can lead to strokes, heart attacks and a sudden loss of blood flow to other organs or to the extremities. About 16 percent of people with PV develop an arterial thrombosis, or blood clot in an artery. About 7 percent develop blood clots in the veins, which can lead to clots in the legs or lungs or in the vein to the liver and spleen.

Speaking of the spleen, 36 percent of people with PV develop an enlarged spleen. Because this organ stores red blood cells and filters out old ones, the high concentration of red blood cells mean that these cells become sequestered in the spleen, causing it to enlarge and compress surrounding structures.

One of the more irritating symptoms of PV is itching, which worsens with exposure to warm water. A more troublesome symptom is a burning sensation in the hands or feet due to alterations of blood flow in the small blood vessels in the feet or hands. This condition, called erythromelalgia, affects 29 percent of patients.

Once a practitioner is clued into the possibility of PV, he or she may order a bone marrow biopsy as well as further blood work, including checking for the mutation in the JAK2 gene.

Phlebotomy is often necessary to lower the red blood cell count, which significantly decreases the risk of blood clots. Low-dose aspirin (81 milligrams) can provide benefit too, not only by reducing the chance of clotting, but by reducing the itching of PV. And, for people over 60, or those with a history of clots, the medication hydroxyurea can help by lowering the red and white blood cell and platelet counts.

As you mention, PV is rare, occurring in 1 out of every 50,000 people per year on average. Although the condition can be life-threatening -- for all the reasons explained above -- the phlebotomies (inconvenient though they are) can help keep the disease under control.

Robert Ashley, M.D., is an internist and assistant professor of medicine at the University of California, Los Angeles.

Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.

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