Why can probiotics and vitamin D significantly affect human health?
Vitamin D deficiency is the most common hypovitaminosis in developed countries. It is largely related to a lack of outdoor activity. Additionally, the typical Western diet does not support a healthy composition of the gut microbiome. Gut dysbiosis, in turn, is associated with both intestinal and systemic diseases. Alongside a healthy lifestyle, probiotics and oral vitamin D supplementation offer solutions.
The Importance of Gut Microbiota
In recent years, terms like intestinal microbiota (a collection of commensal, symbiotic, and pathogenic bacteria) and the human microbiome (their collective genes) have been frequently mentioned as factors that significantly influence human health.
Diet has a direct influence on the composition of the gut microbiome. The microbiome then largely determines the biochemical reactions occurring in the intestinal lumen. The nutrients consumed can be converted by bacteria into biologically active molecules that affect the host's regulatory functions. Bacteria also influence the gene expression of the mammalian intestinal mucosa, thus impacting the functions of the gastrointestinal tract.
Research shows the highest stability of the gut ecosystem with high diversity of bacteria and identifies a composition of the gut microbiome that is beneficial for human health. Dysbiosis, conversely, is primarily associated with idiopathic intestinal inflammation and colorectal cancer.
Mechanism of Probiotic Action
Probiotics can restore a healthy composition of the gut microbiota, supporting its host-beneficial functions, alleviating intestinal inflammation and other intestinal and systemic diseases, or even helping to prevent them. They produce antimicrobial or metabolically active substances that suppress the growth of other microorganisms, or competitively compete for the same receptors and binding sites in the intestinal mucosa. They increase the integrity of the intestinal barrier, thereby reducing bacterial translocation through the mucosa, and influence intestinal immunity and the response of epithelial and immune cells to microbes in the intestinal lumen. Through their effect on the composition of the microbiota, they also influence its overall metabolic functions.
Vitamin D and Its Supplementation, Especially in Children
Vitamin D plays a key role in calcium and phosphate metabolism and is crucial for bone health. Its anti-inflammatory and immunomodulatory effects in the gastrointestinal tract (GIT), influence on intestinal barrier integrity, and intestinal homeostasis, and the potential for interaction between the gut microbiota and exogenous vitamin D have also been described in the literature. Some microbial fermentation products likely support the formation of the vitamin D receptor (VDR), with the vitamin D-VDR complex having potentially modulatory effects on the human microbiome.
A level of 25(OH)D > 50 nmol/l is pragmatically considered sufficient, while a level < 25 nmol/l is considered severe deficiency. The prevalence of vitamin D deficiency is high among European children and adolescents. The most at-risk groups include breastfed infants without recommended vitamin D supplementation, children and adolescents without adequate sun exposure, and obese children.
According to Czech guidelines from 2019 (Bronský et al.), healthy physiological and at-risk newborns and infants should prophylactically receive 400–500 IU of vitamin D per os daily from the second week of life until the completion of the first year of life. The maximum safe dose for infants is considered to be 1,000 IU per day. Healthy children and adolescents should be advised to maintain a healthy lifestyle, with BMI values within the normal range, a diverse diet rich in vitamin D (fish, eggs, dairy products), and adequate outdoor time with sun exposure.
Oral vitamin D supplementation should also be considered for children in at-risk groups from the age of 1 year (routine vitamin D supplementation in older children is not recommended). For these children, it is first necessary to test levels of 25(OH)D, alkaline phosphatase (ALP), parathyroid hormone (PTH), and calcemia, with supplementation always initiated if low 25(OH)D and elevated PTH or ALP levels are found simultaneously. The initial dose in such cases is 1,000–2,000 IU daily, in addition to recommending increased calcium intake in the diet. If a concentration of 25(OH)D > 35 nmol/l is not achieved on the mentioned dose, the dose can be gradually increased up to 4,000 IU in children older than 1 year, with careful monitoring of calcemia and 25(OH)D levels.
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Sources:
1. Hemarajata P., Versalovic J. Effects of probiotics on gut microbiota: mechanisms of intestinal immunomodulation and neuromodulation. Therap Adv Gastroenterol 2013; 6 (1): 39–51, doi: 10.1177/1756283X12459294.
2. Braegger C., Campoy C., Colomb V. et al.; ESPGHAN Committee on Nutrition. Vitamin D in the healthy European pediatric population. J Pediatr Gastroenterol Nutr 2013; 56 (6): 692–701, doi: 10.1097/MPG.0b013e31828f3c05.
3. Bronský J., Kalvachová B., Kutílek Š. et al. Recommended Procedure of the Czech Pediatric Society and the Expert Society of General Pediatricians CLS JEP for the supplementation of children and adolescents with vitamin D. Czech-Slovak Pediatrics 2019; 74 (8): 473–482. Available at: www.pediatrics.cz/content/uploads/2019/10/vitamin_d_finalni_web.pdf
4. Akimbekov N. S., Digel I., Sherelkhan D. K. et al. Vitamin D and the host-gut microbiome: a brief overview. Acta Histochem Cytochem 2020; 53 (3): 33–42, doi: 10.1267/ahc.20011.
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