They gave people 2000 IU vitamin D3 a day for 14 days to see if it lowers cortisol levels.

they gave people 2000 IU vitamin D3 a day for 14 days to see if it lowers cortisol levels.
the results?
cortisol went down 40%

The study
- Effect of vitamin D supplementation on cardiovascular disease risk factors and exercise performance in healthy participants: a randomized placebo-controlled preliminary studyTher Adv Endocrinol Metab · 2016 · PMID 27540461