Effects of Vitamin D on Cardiovascular Health in Black Women

The goal of this clinical trial is to understand the effects of oral vitamin D3 supplementation on various cardiovascular risk factors in generally healthy, young adult black women who are vitamin D deficient or insufficient at baseline. The main questions it aims to answer are: * Does 8 weeks of oral vitamin D3 supplementation (5,000 IU per day) improve 24 hour blood pressure metrics in generally healthy, young adult black women who are vitamin D deficient or insufficient at baseline? * Does 8 weeks of oral vitamin D3 supplementation (5,000 IU per day) improve subjective and objectively estimated sleep health metrics in generally healthy, young adult black women who are vitamin D deficient or insufficient at baseline? * Does 8 weeks of oral vitamin D3 supplementation (5,000 IU per day) improve various measures of blood vessel structure and function in generally healthy, young adult black women who are vitamin D deficient or insufficient at baseline? * Does 8 weeks of oral vitamin D3 supplementation (5,000 IU per day) improve various measures of laboratory blood pressure regulation and autonomic function? All participants will undergo baseline testing, which includes 2 continuous weeks of objective sleep monitoring using a sleep watch, one 24-hour period of ambulatory blood pressure monitoring, and one blood vessel function testing visit. Following baseline testing, vitamin D insufficient and deficient participants will be prescribed take 5,000 IU of vitamin D3 daily for 8 continuous weeks. Participants will undergo 2-weeks of sleep monitoring again during weeks 3-4 of the supplementation period and during weeks 7-8 of the supplementation period. Additionally, 24-hour blood pressure monitoring will be performed during week 4 and week 8, and blood vessel function testing will take place at the end of week 4 and again at the end of week 8. Researchers will assess the effect of the vitamin D3 supplementation intervention by comparing all values between baseline, we