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Has a doctor ever told you that you just have too much blood? Probably not, but there are a handful of conditions where being a little low might be good for you.

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Maybe you’ve heard of bloodletting, the practice of removing blood from patients with the hope of curing some disease or ailment. Turns out, it’s not just some dangerous technique that died off when we figured out better medicine.

It’s not a common treatment anymore, but there are some very specific conditions that might be helped by taking out a little blood. Bloodletting has been around for thousands of years, maybe as far back as ancient Egypt. But it really took off with the Greek physician Hippocrates, who lived around 400 BCE and came up with the idea of the four humors.

Basically, we used to think the human body had four important fluids: phlegm, black bile, yellow bile, and blood. And if they were imbalanced, that could lead to illness. So, why not drain some blood and see if you could cure... well anything from a head cold to a stroke?

Some of the tools that doctors used to cut blood vessels open back in the day, like multi-bladed fleams, give off a horror movie vibe. Or they used leeches as a localized and less intrusive, but equally creepy, approach. One leech can suck around 10 milliliters of blood per feeding, that’s around 10 times its own mass!

Bloodletting stayed really popular through the 17th and 18th centuries. King Charles II was bled after suffering a stroke and George Washington was bled multiple times when he came down with a throat infection. Both died within a few days of the treatment… so, if anything, it probably sped up their demise.

Into the 20th century, most physicians ditched bloodletting for other treatments. And with the discovery of things like antibiotics, the practice dwindled even more. But today, bloodletting has sort of stuck around.

In medicine, it’s referred to as phlebotomy. Instead of using blood-vessel-shredding tools, though, blood is now mostly taken intravenously with tubes, a technique you’d be familiar with if you’ve donated blood. Very few studies have shown conclusive benefits from phlebotomy.

But most hypotheses focus on the role of excess iron in certain diseases. Most of your body’s iron is in your red blood cells in hemoglobin, a protein important for shuttling oxygen through your body. So you want to maintain healthy iron levels.

Too little iron is a well-understood cause of fatigue and has serious consequences for fetal brain development. On the other hand, too much iron is bad too. Iron can accept and donate electrons easily, which is great for shuttling oxygen.

But it can also lead to the formation of free radicals. These highly unstable molecules have unpaired electrons, so they react readily with DNA, RNA, and proteins, and can lead to various diseases. So, one idea is that by reducing excess iron, fewer free radicals will be floating around, and your cells may be safer.

A decade ago, a group of researchers looked into whether phlebotomy could reduce iron levels and lower their risk of developing cancer. They used a pool of over 1200 patients who suffered from peripheral arterial disease, a painful condition where blood vessels are narrow and interfere with blood circulation. And they performed phlebotomy on half of the patients every six months, over the course of a few years.

The researchers found that patients with a lower iron count were significantly less likely to develop a range of cancers, from lung to pancreatic. And the 98 patients who did develop cancer had similar iron levels, whether they were bled or not bled. Phlebotomy patients developed slightly fewer cases of malignant cancer.

But overall, it’s hard to say how much the treatment actually helped with the risk. Some researchers think phlebotomy may help with symptoms of some other diseases. For example, patients with the hepatitis C virus have trouble clearing iron from their systems, because their liver has been damaged, which normally stores and regulates iron.

Although a couple of studies showed a positive change in liver health after phlebotomy, the Gastroenterological Association hasn’t found the evidence convincing enough to recommend it as a treatment. Also, a few studies have looked at phlebotomy in sickle cell disease, where red blood cells take on a somewhat crescent shape instead of a round one. One of the big issues is pain from blocked blood flow, which could potentially be solved by just... removing some.

In one very small case, 7 patients who had frequent phlebotomy treatments for a few years spent less total time in hospitals, just over 30 visits instead of 150. The patients also reported less pain after treatment. But in experiments that rely on self-reporting, the power of the placebo effect can’t be ruled out.

Other studies have indicated positive outcomes too. But patients with sickle cell disease are often receiving other treatments, which makes it hard to tease apart how effective phlebotomy is on its own. Now, all those examples make phlebotomy sound vaguely helpful at best, but it can be life-saving too.

A person with polycythaemia has bone marrow that’s producing too many red blood cells, which could lead to blood clots and serious consequences like permanent organ damage. Routinely removing blood has been shown to improve blood flow and decrease that risk. Plus, even though the idea screams “Middle Ages,” in 2004, the FDA approved the use of leeches in skin graft surgeries.

Leeches have been shown to help healing by removing blood pooled under the skin graft, which helps restore circulation in the blood vessels in a pretty non-invasive way. Leech saliva also contains molecules that stop blood from thickening and platelets from collecting at the wound site. So that helps with reattaching skin with incredibly small blood vessels that clot easily.

In the end, we absolutely shouldn’t be collecting leeches or draining blood with the enthusiasm of a 17th century doctor. But phlebotomy may be a useful treatment under very specific conditions. Thanks for watching this episode of SciShow.

If you want to learn more about dangerous-sounding medical treatments that have stuck around and changed, check out our video on SciShow Psych about electroconvulsive therapy. [ ♪ Outro ].