The goal of this clinical trial is to find out if vitamin D supplements help healthy adults maintain their cognitive and simple physical task performance and emotional state during highly stressful situations.
The main question it aims to answer is:
\- Does vitamin D help maintain cognitive and physical task performance and emotional state during highly stressful situations?
Researchers will compare vitamin D to placebo (a look-alike tablet that contains no active ingredients) to see if vitamin D better maintain cognitive and physical task performance and emotional state during highly stressful situations.
Participants will:
* Take vitamin D or placebo tablets daily for 8 weeks.
* Perform cognitive and simple physical tasks and rate their emotional state under highly stressful situations.
* Wear a stress belt that delivers mild electric shocks 1 - 5 times while participants are performing laboratory tasks.
* Wear a wristwatch-shaped activity monitor for 9 weeks.
* Visit the laboratory 5 times.