Vitamin D and constipation: deficiency or oversupply?
Both a vitamin D deficiency—such as one caused by a disruption of the gut microbiome—and an oversupply that affects intestinal motility have been linked to constipation. A deficiency is present when levels fall below 30 nmol/L, while an oversupply begins at values above 125 nmol/L.
In this article, we explain how vitamin D may be associated with digestive problems and what optimal vitamin D levels should look like. In Germany, an estimated 33–52% of adults and 40–80% of children have an insufficient vitamin D level, with values varying depending on sunlight exposure and the season (Bundesinstitut für Risikobewertung, 2024). The risk of deficiency increases particularly during the autumn and winter months, when there is less sunlight. Studies also show that people in Germany spend over 90% of their time indoors (Zeit, 2023).
Table of Contents
- What is vitamin D and why is it important?
- How does a vitamin D deficiency affect digestion?
- How does a vitamin D oversupply affect digestion?
- What other symptoms occur with vitamin D deficiency or excess?
- What causes vitamin D deficiency or oversupply?
- Summary
What is vitamin D and why is it important?
Vitamin D is a fat-soluble vitamin that exists in two main forms: vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). It is unique in that our bodies can produce it naturally through the skin when exposed to sunlight. In small amounts, it is also found in foods such as fatty fish, eggs, and fortified products. Vitamin D plays a critical role in several bodily functions.
Important functions of vitamin D include:
- Regulation of calcium and phosphate metabolism for healthy bones and teeth
- Supporting the immune system in fighting infections
- Promoting muscle function
- Supporting cell division and renewal
- Maintaining cardiovascular health
Sources: Mayo Clinic, 2023; NIH, 2024
Vitamin D levels and how to interpret them
Vitamin D is measured using two units: ng/ml (nanograms per milliliter) and nmol/l (nanomoles per liter). These units are based on different measurement systems used in various countries. The table below provides general guidelines for vitamin D levels. However, individual needs may vary.
| Vitamin D (ng/ml) | Vitamin D (nmol/l) | Meaning |
|---|---|---|
| < 30 | < 12 | Deficient supply |
| 30 - < 50 | 12 - < 20 | Suboptimal supply |
| 50 - < 125 | 20 - < 50 | Adequate supply |
| ≥ 125 | ≥ 125 | Oversupply |
Source: NIH, 2024
Recommendations:
- In the case of low vitamin D levels, it is recommended to increase sun exposure, take supplements if advised by a doctor, and adjust the diet to include vitamin D-rich foods such as fatty fish and eggs.
- In the case of high vitamin D levels, supplement intake should be reduced or discontinued, and both calcium and vitamin D levels should be monitored by a physician.
- In the case of abnormal levels, regular testing may be helpful to ensure optimal supply.
Would you like to check your vitamin D level?
With Homed-IQ's vitamin D test, you can conveniently measure your blood vitamin D level at home and determine whether you may be suffering from a deficiency. In addition to vitamin D, the vitamin deficiency test also allows you to test for other important vitamins such as B12 and folic acid (B9). Test results are evaluated in ISO-certified laboratories that are also used by medical practices and clinics.
How does a vitamin D deficiency affect digestion?
A vitamin D deficiency can negatively affect digestion, particularly through its impact on the gut microbiome. The microbiome is the community of microorganisms—such as bacteria, fungi, and viruses—that inhabit the gut and are essential for digestion and immune function. An imbalance in the microbiome, also known as dysbiosis, is associated with numerous problems, including digestive disorders, autoimmune diseases, and weakened immune responses (Cleveland Clinic, 2024).
Studies have shown that vitamin D influences the composition of the microbiome. High vitamin D levels promote beneficial bacterial species such as Akkermansia and Bifidobacterium, which are important for healthy gut function, and reduce harmful bacteria. Vitamin D also appears to strengthen the intestinal barrier, which protects the body from harmful bacteria. A deficiency can weaken this barrier, increasing the risk of inflammation and contributing to digestive issues like constipation. Microbiome changes caused by a vitamin D deficiency can slow intestinal motility and impair nutrient absorption (Yamamoto & Jørgensen, 2020; Luthold et al., 2017; Singh et al., 2020).
How does a vitamin D oversupply affect digestion?
An excess of vitamin D can occur when high doses of supplements are taken. Elevated vitamin D levels can lead to hypercalcemia, as too much vitamin D increases calcium absorption in the intestines, resulting in elevated calcium levels in the blood. This can impair intestinal motility by disrupting nerve and muscle activity in the intestines, which may lead to constipation. Hypercalcemia can also interfere with water absorption in the intestines, making bowel movements more difficult and increasing the likelihood of constipation (Mayo Clinic, 2022).
What other symptoms occur with a vitamin D deficiency or excess?
In addition to changes in digestion, there are other symptoms associated with a vitamin D deficiency or excess. An overview is provided in the following chart:
Source: Cleveland Clinic, 2022
What causes vitamin D deficiency or oversupply?
Both a deficiency in vitamin D and an oversupply (hypervitaminosis D) can lead to health issues. The following risk factors are key to the development of vitamin D deficiency or hypervitaminosis D.
| Risk factors for vitamin D deficiency | Risk factors for hypervitaminosis D |
|---|---|
| Lack of sun exposure | Excessive intake of vitamin D supplements |
| Dark skin pigmentation, as this reduces vitamin D synthesis | Lack of monitoring during intake of high-dose vitamin D supplements |
| Older age, which is also associated with reduced vitamin D production | |
| Inadequate dietary intake of vitamin D | |
| Certain medical conditions that impair vitamin D absorption (e.g. celiac disease) |
Sources: NIH, 2024; Cleveland Clinic, 2023
Summary
Vitamin D plays a crucial role in the health of bones, muscles, and the immune system, as well as in maintaining a healthy digestive function. Both a deficiency and an oversupply—though the latter is rare—can be associated with constipation. Understanding risk factors and conducting regular tests can help prevent such issues.
