Irritable bowel syndrome (IBS) is a chronic and debilitating functional disorder of the gastrointestinal tract with serious and detrimental impacts on quality of life. Its aetiology is largely unknown and the identification of effective management strategies remains far from complete. This paper first reports, a case of a 41-year-old woman IBS sufferer who reported significant symptom improvements with high-dose vitamin D3 supplementation. The sufferer identified a substantial body of patient data surrounding this potential therapy on social media sites, and this paper, therefore, also reports the findings from a systematic analysis of patient-centred, internet-based data surrounding this phenomenon. Data from 37 IBS sufferers commenting on the effect of vitamin D supplementation on their condition were located; approximately 70% of these reported that high-dose supplementation improved their IBS symptoms. A randomised controlled trial into the effect of vitamin D supplementation on IBS symptomatology to test this association scientifically is merited.