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Vitamin D is a potent immune modulator with pleiotropic effects on gastrointestinal homeostasis. In this study, researchers determined the levels of circulating 25-hydroxyvitamin D in 77 children with acute diarrhea and evaluated its relationship to their disease severity.
Digestive Health
Vitamin D is a fat-soluble vitamin that plays a key role in calcium homeostasis and innate immunity. Vitamin D promotes antimicrobial peptide gene expression and increases phagocytic function through up-regulation of the AMP-dependent protein NO synthase (PLASMA).
This is likely to explain the reduced diarrheal risk associated with adequate vitamin D intake in some studies. However, a higher risk of diarrhea in vitamin D deficient children could also be attributed to genetic variation in the vitamin D-binding protein (DBP) which influences the bioavailability of serum 25-hydroxyvitamin D. This is important because DBP polymorphisms have been shown to impact the outcome of RCTs in terms of calcemic and non-calcemic outcomes.
Diarrhea is characterized by loose, watery stool that can occur three or more times per day or as often as every two to four weeks. Symptoms of acute diarrhea usually last for a day or two, while chronic or persistent diarrhea is more frequent and can persist for up to four weeks. Vitamin D is not known to cause diarrhea or cramping when taken at doctor-recommended doses and as part of a balanced diet, but can lead to gastrointestinal distress in those with low levels of vitamin D. This can be a result of low intestinal absorption or toxicity from excessive doses of supplements that contain vitamin D.
Vitamin D Effects
A number of studies have examined vitamin D effects on diarrhea. They include two cohort and three cross-sectional studies as well as one randomized controlled trial (RCT). All 9 included primary studies and evaluated the association between diarrhea and vitamin D status, defined by either serum 25-hydroxyvitamin D or vitamin D binding protein levels, using these markers as surrogate markers of vitamin D.
The results of these studies show mixed results. For example, in the study by Mahyar et al, vitamin D deficiency was associated with increased and decreased diarrhea risk in different age groups. This heterogeneity in vitamin D effect is likely due to differences in the diversity of gut microbiota as children grow older.
Vitamin D is important for calcium homeostasis and immune function. It also modulates inflammatory responses to enteric pathogens and promotes production of gut antimicrobial peptides.
Although it is possible to overdose on vitamin D, toxicity is uncommon and symptoms are rare. Signs of vitamin D toxicity include confusion, frequent need to urinate, thirst and muscle weakness. If you experience these symptoms, seek medical care immediately. For irritable bowel syndrome, vitamin D supplementation has been shown to improve quality of life in patients with a low level of vitamin D. However, you should consult with your doctor before taking a vitamin D supplement to ensure that it won’t interfere with other medications you are taking.
Expert View
Vitamin D is consistently hailed as a crucial nutrient and essential for overall health and well-being. However, could this much-loved nutrient actually be to blame for a not-so-genteel health concern, such as diarrhea?
The pleiotropic nature of vitamin D makes it a key player in enteric immunologic function. This includes the promotion of gut antimicrobial peptide gene expression and up-regulation of nitric oxide synthase. These pathways help to deter microbial invasion into the gastrointestinal tract and thereby prevent infectious diarrheas.
Researchers have observed that malnourished children are at greater risk of developing bacterial diarrhea. This is due to the less mature and more limited gut microbiota in these malnourished individuals. In addition, a high prevalence of vitamin D deficiency in these populations is also associated with lower immunity against diarrheal pathogens.
Researchers have also observed that the use of oral vitamin D supplements reduces the risk of diarrhea. This is largely due to the fact that higher blood levels of this nutrient inhibit the production of calcitriol, which promotes the production of antimicrobial peptides and nitric oxide synthase in macrophages. In a recent randomized controlled trial, quarterly supplementation of 100 000 IU of vitamin D3 (cholecalciferol) did not significantly reduce the incidence of first or recurrent diarrheal illness in a high-risk population of children in Kabul, Afghanistan. Further research is needed to identify appropriate serological levels and immune mechanisms of vitamin D that enhance intestinal immunity against diarrheal disease.