The Efficacy of Vitamin D Supplementation to Sustain Performance Outcomes

Inclusion Criteria: * Male and non-pregnant, non-lactating females 18 to 40 (inclusive) years of age. * Females of child-bearing potential must be using some form of birth control, if sexually active (e.g., oral contraceptive, condom, intrauterine device, etc.) * Score of 80% or greater on a "Volunteer Comprehension Assessment" test. A maximum of two attempts is permitted. * Blood 25 hydroxy vitamin D \[25(OH)D\] levels at the Screening visit of 30 nmol/L (12 ng/mL) (inclusive) - \< 75 nmol/L (30 ng/mL). Exclusion Criteria: * Contraindications due to vitamin D supplementation, including a history of hypercalcemia, malabsorption syndrome, hypervitaminosis D, or allergic/hypersensitivity reactions to vitamin D or a history of other adverse reactions to vitamin D supplementation. * Taking a vitamin D3 or D2 supplement or a supplement containing vitamin D3 or D2 (excluding vitamin D-fortified foods) during the participation. Volunteers who take vitamin D3 or D2 supplement before their participation can be eligible if they agree to stop taking the supplement(s) starting 1 month prior to the enrollment/baseline visit until the end of the post-supplementation visit. Blood 25(OH)D levels of the volunteers who stopped taking the supplements after the screening visit will be tested before the Enrollment/Baseline visit to ensure their 25(OH)D fall within the inclusionary ranges. Volunteers who are not able to stop taking vitamin D supplements or supplements containing vitamin D due t…