To obtain sufficient specimens and correlating clinical data from a well-controlled prospective clinical trial collecting specimens from healthy subjects t on vitamin D assays, and to establish a collection of specimens that will support future assay discovery and validation efforts.

1. Obtain matched serum and plasma specimens collected from a minimum of 50 healthy subjects in two geographic areas. Specimens will be used to determine a reference range for a vitamin D assay, used as an aid in the assessment of vitamin D sufficiency in adults.
2. Obtain serum specimens collected from a minimum of an additional 450 healthy subjects in two geographic areas. Specimens will be used to determine a reference range for a vitamin D assay, used as an aid in the assessment of vitamin D sufficiency in adults.
3. To store any remaining specimens for use in future vitamin D assay development and to evaluate as yet undetermined assays for the development of IVDs, including additional vitamin D assays

Inclusion Criteria:

Males and females, age≥ 18 years Able to understand and willing to provide informed consent

Exclusion Criteria:

Males and females, age <18 years Current use of dietary supplements (tablet, liquid gel or liquid form only) containing high concentrations, greater than 2,000 IU per day, of vitamin D.

Has a history of vitamin D deficiency Has a history or current diagnosis of any clinically significant cardiac, respiratory, neurological, immunological, hematological, liver disease, renal disease, gastrointestinal (GI) disorder, including any history of peptic or gastric ulcers or GI bleeding, or any other condition which, in the opinion of the investigator is considered chronic.

Personal history of seizures Personal history of bariatric surgery Personal history of parathyroid and thyroid disease Pregnancy or lactation Is receiving systemic chemotherapy or radiation treatment, has an active malignancy of any type, or has been diagnosed with cancer within 5 years before screening other than basal or squamous cell skin cancers or in-situ cervical cancer.

Family history of parathyroid or calcium regulatory disease Medications known to affect absorption e.g. drugs that inhibit cholesterol absorption Medications known to increase catabolism such as anticonvulsants, glucocorticoids, HAART (AIDS treatment) and anti-rejection medications Unable to provide informed consent

Healthy men and women greater than or equal to 18 years of age