Bloodletting (הקזת דם) was a commonplace medical procedure in the Mishnaic times (see Shabbos 129). It is widely accepted that the ancient healers believed that:

"... many diseases were caused by plethoras, or overabundances, in the blood... "Bleeding" a patient to health was modeled on the process of menstruation. Hippocrates believed that menstruation functioned to "purge women of bad humors". During the Roman Empire, the Greek physician Galen, who subscribed to the teachings of Hippocrates, advocated physician-initiated bloodletting... The Talmud recommended a specific day of the week and days of the month for bloodletting... (WIKI ibid)"

Rambam started to treat the bloodletting with more caution (Deos 4,14):

"לא ירגיל אדם עצמו להקיז דם תמיד, ולא יקיז דם אלא אם היה צריך לו ביותר; ...".

We also know that hurting oneself is a transgression, and today the bloodletting would be forbidden after proven seriously wrong. The Sages themselves saw a great danger in it.

I wonder if the Sages' practice of bloodletting was based purely on the medical customs of the leading "scientists" of their times, or had some Jewish traditional roots?

Please notice, this question is not about the benefits/dangers of bloodletting, but about its origin.

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    From: rasmussen.edu/degrees/health-sciences/blog/… - 2. Giving blood can reduce harmful iron stores One in every two hundred people in the U.S. is affected by a condition called hemochromatosis and most don’t even know it, according to Patenaude. Hemochromatosis is a disease that causes an iron overload and is labeled as the most common genetic disease among Caucasians by the Mayo Clinic. – Loewian Mar 6 '19 at 14:45
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    3. Giving blood may lower your risk of suffering a heart attack Donating blood at least once a year could reduce your risk of a heart attack by 88 percent, according to a study conducted by the American Journal of Epidemiology.* This relates to the iron issue again, says Dr. David Dragoo, healthcare expert at Money Crashers. – Loewian Mar 6 '19 at 14:47
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    4. Giving blood may reduce your risk of developing cancer In an average, completely healthy person, the link between giving blood and decreased cancer risk is slim. But research does support a reduced risk of cancer for blood donors with different maladies, one of which is hemochromatosis. – Loewian Mar 6 '19 at 14:47
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    Phlebotomy (the process of drawing blood) was found to be an iron-reduction method that is associated with lower cancer risk and mortality, according to a study published by the Journal of the National Cancer Institute. The study focused on patients affected by peripheral arterial disease (PAD), which the Mayo Clinic describes as a common circulatory problem. PAD patients who regularly donated blood had a lower risk of developing cancer than those who did not. – Loewian Mar 6 '19 at 14:48
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    5. Giving blood can help your liver stay healthy Another danger of iron overload is the health of your liver. “In recent years, nonalcoholic fatty liver disease (NAFLD), the hepatic expression of metabolic syndrome, has reached epidemic proportions,” reports the National Center for Biotechnology Information. Research has linked too much iron with NAFLD, Hepatitis C and other liver diseases and infections. Though there are many other factors involved in these problems, donating blood can help relieve some of those iron stores and avoid extra issues in your liver. – Loewian Mar 6 '19 at 14:48

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