The Risks and Benefits of Epsom Salt for Constipation

Lifestyle approaches to constipation include things like encouraging patients to eat breakfast with a hot beverage to help kick off the gastrocolic reflex, which I’ve talked about before, but the preached holy trinity is dietary fiber, fluids, and exercise. I’ve got lots of videos on fiber. Exercise-wise, population studies don’t clearly show an association between constipation and physical activity after other factors like fiber consumption are taken into account, but you can’t know for sure until you put it to the test.

Inactivity does seem to slow things down. If you force active older individuals to become sedentary (dropping step counts from about 13,000 to 4,000 a day), within two weeks you can nearly double their colonic transit time (the time it takes food to get from mouth to anus) which can be measured using the “blue poo” test with food coloring or by just eating some beets. Conversely, even mild physical activity has been shown to reduce symptoms of abdominal distention and bloating. What about constipation?

There have been nine randomized controlled trials of exercise for constipation, and moderate aerobic exercise like walking 20 minutes a day was shown to improve mild constipation symptoms, but it is unlikely to have an effect in patients with severe constipation. What about fluids?

Constipated patients don’t seem to drink any fewer fluids than non-constipated controls, leading reviews to conclude that increasing water intake is unlikely to be helpful, but again, that’s something to be determined by interventional studies. I was only able to find three. One involved upping the fluid intake of normal healthy volunteers with one or two liters a day of water or Gatorade and found no change in stool output. But what we really want to know is what happens in constipated individuals, which thankfully the other two studies did.

One study involved a randomized trial of the effects of sparkling versus still water. The researchers found that drinking carbonated water appeared to improve symptoms of constipation (as well as feelings of stomach upset), though it’s not clear if sparkling beat out the tap water control group. The third study did find a significant effect of increased fluid consumption, though. More than a hundred men and women having fewer than three bowel movements a week were randomized to continue their usual habits or to drink two liters of mineral water a day, preferably between meals for two months. Compared to the control group, the water group increased stool frequency by an average of one extra one per week, along with one fewer weekly laxative dose. Because they used mineral water, though, we don’t know if it was the water or the minerals.

Mineral waters rich in magnesium sulfate (known as Epsom salt) have been used for centuries to treat constipation, and randomized, double-blind, placebo-controlled studies have since demonstrated their efficacy in terms of improved stool consistency and number of bowel movements. These were the tested brands. You could recreate the magnesium content by adding a quarter teaspoon (1.50 ml) of food-grade Epsom salts to a quart (0.95 L) of water, but be careful not to overdo it. Deaths due to magnesium overload have been documented for more than a century, for example in a case of a practical joke gone awry involving slipping large amounts of Epsom salts into someone’s beer. Adults with good kidney function should not exceed more than two to four level teaspoons (11.8 ml to 23.70 ml) in a full glass of water twice a day. Keep out of reach of children, and talk with your healthcare practitioner before use if you have kidney disease.

Minerals can also be introduced in the opposite direction via a sodium phosphate enema, like Fleet, but this is not recommended due to the risk of inducing an electrolyte imbalance, as the phosphorus can be absorbed into the bloodstream from the colon. Instead, warm tap water enemas appear to be the safest option, triggering the urge to defecate when used in volumes greater than about a half cup (120 ml). However, the best remedy for constipation may be to treat the cause, by ensuring an adequate intake of fiber-rich foods.