Although dietary vitamin D supplementation has been used in the clinical setting for decades, the effect of supplementary vitamin D consumption on the structure of the microbiome has not been studied in humans in fine scale or with concomitant adjustment for dietary intake. Understanding the interaction of vitamin D with the microbiome in humans could lead to important advancements in the understanding of how vitamin D together with diet impacts the microbiome composition, and ultimately, risk of EOCRC. This study has the potential to lay the ground work for an adjunctive therapy to manipulate the microbiome to reduce risk of EOCRC. This proposed study is designed to evaluate the effect of vitamin D supplementation on the normal structure of the microbiome and data will not be used to diagnose, prevent, cure or treat disease.

Inclusion Criteria:

• Adult 18 years or older

Exclusion Criteria:

• Women who are currently pregnant or breastfeeding
• Use of antibiotics within the last 2 weeks
• Use of supplementary vitamin D within the last month
• Self-reported, pre-existing history of inflammatory bowel disease, heart disease or diabetes
• Students under 18
• Tanning/sun exposure > 60 min at a time in last 4 weeks
• No phenobarbital, carbamazepine, spironolactone chronic therapy; or steroid use within the last 2 weeks
• Severe allergy to ingredients found in supplements

Study participant de-identified data will be shared with other researchers who submit a request for data acquisition. An MTA agreement will be constructed for protection of data sharing between the two researchers.

Data will become available at the time of publication in peer-reviewed journal for 10 years.

Signed MTA agreement between study sponsor and requesting entity.

Participants, investigators and outcomes assessors are masked to intervention group assignments using a researcher outside the study that maintains the study codes and IDs