Modelling the influence of vitamin D and probiotics on inflammation and the intestinal microbiota in older adults.

The relationship between the intestinal microbiota and human health during ageing is an area of increasing interest due to increasing health challenges experienced by ageing populations. This paper develops a mathematical model describing the age-related biological changes associated with alterations to the microbiota, vitamin D levels, immunosenescence and inflammageing to determine the likely impact of manipulating the intestinal microbiota with dietary components. Age-dependent parameters are incorporated into a previously developed model to determine the evolution of intestinal bacterial populations, vitamin D receptor:1,25 dihydroxyvitamin D levels, epithelial barrier integrity and immune response with increasing age. Results suggest an age-related decline in both innate and adaptive immunity, weakening of the intestinal barrier, elevation in systemic inflammation and reduced serum vitamin D, resulting in individuals over 60 years old becoming vitamin D deficient (<50 nmol/L). Numerical simulations indicate that administration of probiotics and/or vitamin D supplements upregulates the VDR complex at all ages, which helps restore epithelial barrier function, particularly in older adults in whom the intestinal barrier has been compromised. The greatest benefit is derived from co-supplementation with probiotics and age-dependent doses of vitamin D. Finally, the value of gathering additional experimental data motivated by the modelling insights is discussed.