The proposed study will examine vitamin D bioavailability when 20µg of vitamin D is consumed in 5 different forms:

i) a vitamin D enriched pre-formed mixed micelle dairy drink ii) a vitamin D enriched olive oil dairy drink iii) a vitamin D enriched fish oil dairy drink iv) a vitamin D enriched fat-free dairy drink

This postprandial study will recruit healthy males and females aged 18 and over. Upon completion of informed consent procedures and successful screening, the volunteers will complete 4 study visits. Participants will consume a standardised meal the evening before each test day, and will arrive in the morning to the research facility in UCD after an overnight fast of 12 hours.

On the study test days, volunteers will be given one of the following vitamin D treatments in a dairy drink, followed by a low-fat breakfast.

1. mixed micelles
2. olive oil
3. fish oil
4. fat-free

Participants will also be given a low-fat lunch 5 hours after the supplement is consumed. Volunteers will be cannulated by a trained phlebotomist on arrival, and a fasting blood sample will be taken. Following ingestion of the vitamin D supplements blood samples will be taken at 0,2,4,6, and 8 hours post ingestion. A 10mL sample will be collected at each time point. In total, 60mL of blood will be collected over 24 hours. The participant's food intake will be recorded during the visit.

Inclusion Criteria:

Healthy men and women

Exclusion Criteria:

Pregnant or lactating Smokers Individuals that are not free-living e.g. institutes where meals are prepared in bulk such as nursing homes, prisons etc.

An inability to read, write or understand English Following a strict prescribed diet for any reason, insulin dependent diabetes, coeliac disease, Crohn's disease Disease or condition that requires chronic therapeutic nutritional or medical treatment.

Those taking supplemental vitamin D Those who have been on a sun holiday in the last 2 months

At the start of the study each participant will have a study code assigned to them. All of the data from the trials will be stored using these unique study codes. A file will be set up which will be stored in a location separate to the study data. This file will contain a list which will link each participants contact details to the corresponding ID code. All stored information will be encrypted and protected by a password that only the researcher and PI will know.

single-blinded crossover study