Does Vitamin D Cause Constipation?

Health experts agree that vitamin D promotes a well-functioning body and optimum health. Fortunately, there are several ways to get vitamin D through diet and sun exposure. But is there a link between increasing vitamin D intake and our gut health, particularly when it comes to constipation? And can too much of a good thing ever be bad for us? While it seems more research needs to be done in order to understand the relationship between vitamin D and constipation, health experts are finding varying data.

For instance, one group of researchers focused on IBS sufferers to best study the potential link between vitamin D and constipation (via the European Journal of Nutrition). IBS sufferers not only commonly experience constipation, but also typically have low levels of vitamin D. The researchers found that upon vitamin D administration, participants had an increase in vitamin D levels over the placebo group, but there were no effects on IBS symptom severity or an increased quality of life. This suggests that increased vitamin D intake may not improve IBS symptoms such as constipation. 

However, a different 2019 study found that patients with intestinal motility disorders had lower vitamin D levels, and that vitamin D supplementation potentially acted as a therapeutic aid for the illnesses (via the World Journal of Gastroenterology). Principal investigators of the study admitted that further research needs to be conducted, though, and that the causative role of vitamin D in the process is still unclear.

When vitamin D can cause constipation

Although some researchers suggest vitamin D can alleviate constipation, other health experts warn that too much vitamin D can actually increase one's chances of constipation, especially if taken above the recommended dose.

Hypercalcemia is a condition in which blood calcium levels become too high and can occur as a result of taking excessive amounts of vitamin D over time, per the Mayo Clinic. A common symptom of hypercalcemia is constipation. However, when vitamin D is taken in the right amounts, it is generally considered safe and well-tolerated. The recommended daily limit of vitamin D intake is 400 international units (IU) for children younger than 12 months, 600 IU for persons between 1 and 70 years of age, and 800 IU for people over 70 years old (via the Mayo Clinic). Those taking more than 4,000 IU per day are at greater risk of negative health impacts and gastrointestinal side effects such as constipation. 

It's important to work with your doctor to determine the best course of action for safely increasing your vitamin D intake, especially if you're concerned about constipation and other side effects. Your doctor will likely be able to assess your particular situation and come up with a tailored supplemental regimen that works best for you.