Inclusion Criteria:  Aged 16 years or over. Resident of the United Kingdom  Exclusion Criteria:  The inability to provide informed consent. Under the age of 16 years. A non-UK resident.  Patients who may be at increased risk from rigid sigmoidoscopy:  Individuals who are taking anti-coagulation medication. Individuals with platelet disease or other bleeding issues. Individuals with a history of a significant rectal bleed. Suspected or known bowel perforation Anal stenosis Acute peritonitis Colonic necrosis Toxic megacolon Acute severe diverticulitis Diverticular abscess Recent colonic surgery Anal fissure Severe coagulopathy Anticoagulant therapy Severe thrombocytopenia Severe neutropenia  Patients who may be at increased risk from Vitamin D supplementation would not be included in the intervention arm but could still be included in the single sample arm:  Kidney disease High levels of calcium in the blood Atherosclerosis Sarcoidosis Histoplasmosis Over-active parathyroid gland (hyperparathyroidism) Lymphoma Currently taking thiazide diuretics, digoxin or other cardiac glycosides Known allergy to nuts ( as peanut oil contained within vitamin D preparations) Female subjects of child bearing age who are not taking effective contraception during the period of the trial  Patients in whom vitamin D levels may be unpredictable  Individuals already established on supplementary Vitamin D. Individuals recently returned to the UK from an overseas holiday. Individuals who have recently lived abroad. Patients on anti-epileptic medication