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Taurosodeoxycholic acid, or TUDCA, is a bile salt and liver supplement naturally produced by our gallbladders that has many health benefits. There are many different types of bile produced in the body, mostly used in digestion. TUDCA is used for protecting the liver and the nervous system from damage. 
It has a long history of use as an oral bile salt therapy in traditional Chinese medicine as “bear bile.”  Traditionally, this is extracted from hunted or farmed Asiatic black bears (also known as the moon bear) or more recently from the American black bears, which have more TUDCA in their bile than humans do.
However, TUDCA can also be made without harm to animals, using modern techniques that use the chemical taurine to produce it in laboratories. 
Benefits and Effects
TUDCA has an advantage over many other treatments wide range of effects in the body, its easy use, and a lack of side effects. TUDCA works either by its interactions with other bile salts or by preventing cells from self-destructing (a process known as apoptosis.) 
Taking bile salts is a long-established way for people to prevent gallstones.  TUDCA in particular is easily absorbed by the body, which then stores TUDCA in the gallbladder. This changes the chemical composition in the organ and prevents cholesterol from being secreted there. Gallstones are made from cholesterol, which is usually digested in the gallbladder. When there is too much for the gallbladder to handle, it can clump together into gallstones. TUDCA prevents too much cholesterol from being secreted into the gallbladder, preventing gallstones from forming.
TUDCA also helps to dissolve gallstones that may already be forming. 
Diabetes and Hyperglycemia
TUDCA is not a diabetes treatment on its own. However, it can be added to other diabetes treatments to normalize blood sugar (glycemic) levels. 
TUDCA can help with diabetes by making the liver and the muscles more sensitive to insulin, allowing them to use glucose more effectively and cause fewer blood sugar drops and spikes.  Though TUDCA does not affect insulin resistance in fat cells, it does reduce inflammation and the stress this causes for the fat cells, which allows them to function in a healthy way. TUDCA may also protect the insulin-producing islet cells in the pancreas from being damaged and dying off. 
TUDCA helps to dilute bile that sometimes gets built up in the liver. If these bile salts weren’t diluted, they could start “digesting” the liver tissue around it — TUDCA gives the liver protection from damage, measured by decreased liver enzymes in the bloodstream. 
By preventing damage to the liver from its fellow bile salts, and by protecting the cells from the inside, TUDCA can be used as a therapy for fatty liver disease, primary biliary cirrhosis, chronic hepatitis disease, and liver problems caused by cystic fibrosis. [10, 11, 12] Reducing damage also allows the liver to repair itself and recover. [13, 14]
It’s best used early in the course of the disease to reduce the scarring and loss of function that can result from long-term disease which can only be healed to a limited degree.
TUDCA also protects the liver from damage caused by sleep apnea, a condition where people stop breathing temporarily during the night. The lack of oxygen can damage organs by causing oxidative damage and increasing stress on cell structures – TUDCA prevents this liver damage and alleviates this stress. 
The kidney is a hard-working organ that can sometimes be overworked and become damaged as a result. TUDCA reduces some of the stress on the endoplasmic reticulum protecting the kidney against injury from toxins, diseases, and normal wear and tear. 
Irritable Bowel Syndrome
While TUDCA alone is not a cure for irritable bowel syndrome, it does make the symptoms less intense and improves the diversity of the bacteria in the bowels and digestive system. This prevents the disease from progressing and makes you healthier.  How TUDCA helps with irritable bowel is unknown.
TUDCA is remarkable for being a clinically safe, oral bile salt therapy that can cross into the brain and prevent many forms of brain damage. This includes stroke damage, which is caused when the brain cells stop receiving oxygen due to a blockage in the blood vessels that feed the brain. While strokes will always cause some damage, people on TUDCA experience less – nearly half as much in some studies — damage from strokes and better healing over time. 
This may be because much of the damage from a stroke occurs when nerve cells die after the fact from the stress that was put on them and their internal structures.  Because TUDCA protects those internal structures, blocks the self-destruct signals from killing the cell, and helps the cell fold its proteins more effectively. It may give those nerve cells the time they need to recover, and an extra chance to heal. 
TUDCA has use in Parkinsons, Alzheimer’s, Huntington’s, ALS, Friedrich’s Ataxia, and other neurodegenerative diseases by protecting neurons in the body and the brain from dying. This protective property is mostly for the same reasons that it protects against stroke damage – much of the nerve damage is from apoptosis, which TUDCA prevents from happening. [1, 20, 23]
TUDCA’s effects could also include “fixing” the defective proteins that cause these diseases to some extent by encouraging to fold properly or by changing the expression of their genes. There isn’t much evidence to how that might be happening, but TUDCA has been shown to slow the progression of neurodegenerative diseases and to reduce their symptoms. 
TUDCA reduces stress on the rod cells (the parts of the eye that detect light and color) and keeps them from being damaged and dying from apoptosis. [25, 26] TUDCA also slows glaucoma and cataract formation by acting as an antioxidant and protecting the cells from damage from high oxygen levels. [1, 2]
How TUDCA Works
TUDCA is water soluble, not fat soluble like other bile salts. This means that it does not have a detergent-like effect, making it less damaging.  When it is taken as an oral bile salt therapy, it acts as a liver detox: it dilutes the bile salts that get stored up in the liver, it prevents them from causing damage, and it gives the liver a chance to heal from any existing damage.
TUDCA is an antioxidant as well, protecting cells from damage. More specifically, though, it prevents cells from becoming overstressed and self-destructing, a major cause of cell damage in strokes, neurodegenerative diseases, and other problems. It does this through two methods: By taking some of the pressure off of a cell structure called the Endoplasmic reticulum and by interfering with cell signals that tell the mitochondria (the powerhouses of the cell) to break apart and die. 
Because it can cross the blood-brain barrier, it can protect the brain, where many drugs cannot reach.
The Endoplasmic Reticulum
The endoplasmic reticulum or ER is a special structure in the cell that helps proteins – the building blocks of life – fold into the correct shapes, often as they are being produced in the cell. TUDCA doesn’t interact with the endoplasmic reticulum directly. Instead, it gives the ER less work to do by giving the proteins some folding help of its own.  This process is called “chaperoning” and means that fewer proteins need the help of the ER to fold.
The ER becomes stressed in many damaging or degenerative diseases, where important proteins begin to fold improperly due to age or damaged mechanisms in the cell. It becomes too much for the structure to handle. With TUDCA’s help, the ER becomes less stressed, and a less-stressed ER is less likely to trigger self-destruct sequences in the cell and add to the damage in the body. [8, 16]
TUDCA protects the membranes surrounding the mitochondria – tiny structures that produce energy for the cell – from damage. This damage can come from oxidative stress, the consequence of free oxygen radicals that are produced as a waste product from the mitochondria, or from other problems in the cell. TUDCA also blocks self-destruct signals from reaching the mitochondria, keeping them running. [1, 23, 27]
TUDCA vs UDCA
Ursodeoxylcholic acid or UDCA works much like TUDCA in the body, with the same benefits and the same low risk of side effects and may sometimes be studied instead of UDCA. However, the advantage of TUDCA is that it is better absorbed and stored by the body, meaning that a dose of TUDCA would have a larger benefit than the same dose of UDCA.  Therefore, TUDCA is better to take. 
TUDCA is taken orally, and the dosage varies depending on what the TUDCA is being used to treat. There does not seem to be anything tied to the amount of TUDCA taken.
How much TUDCA should you take?
To protect the liver, about 10-13mg are used daily.
To change the concentrations of bile salts in the body for various health effects, this dose is raised to about 15-20mg/kg of body weight.
To treat insulin sensitivity or fatty liver, this dose can be as high as 1750mg daily, which is the highest dose known to be medically useful.
Higher doses reduce cholesterol but have few other additional benefits or side effects. 
While you should always consult a doctor before adding a supplement to your regimen, tauroursodeoxycholic acid has few side effects, even at high doses and used in the long term.
The most common, and possibly the only, side effect on record is diarrhea, which is usually not severe enough to be life-threatening. 
TUDCA has no reported interactions with statins or other drugs,
TUDCA can be taken with taurine and choline. TUDCA may also be taken with statins, diabetes drugs, and other antioxidants. It is not known to interact with other supplements or drugs and can be taken with or without food.
TUDCA vs Milk Thistle
Milk thistle supplements (silymarin) has similar effects in the body to TUDCA. Milk thistle can be taken with TUDCA (with caution) or on its own. However, milk thistle has a high risk of allergic reactions, higher risk of side effects, and lower effectiveness, making TUDCA a better option to take on its own. [30, 31]