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 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 vitamin D3 supplementation (5,000 IU per day) improve objectively estimated sleep duration and regularity in generally healthy, young adult black women who are vitamin D deficient or insufficient at baseline? Does 8 weeks of 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? 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, week 4, and week 8 to see if there is any effect of vitamin D3 supplementation on 24-hour blood pressure, sleep duration and regularity, and blood vessel structure and function following 4 and 8 weeks of supplementation.

All participants will receive the same intervention: 8 weeks of daily oral vitamin D3 supplements, each containing 5,000 IU

Change in 24-hour ambulatory systolic and diastolic blood pressure (mmHg) using an at-home ambulatory blood pressure monitor.

Participants will undergo a 24-hour period of ambulatory systolic and diastolic blood pressure (mmHg) recording to evaluate diurnal systolic and diastolic blood pressure and nocturnal systolic and diastolic blood pressure.

Change in objectively estimated sleep duration and sleep regularity using a Philips Actiwatch Spectrum Plus accelerometer wrist watch

Participants will undergo a two-week period of objectively estimated sleep recording using the Actiwatch. Sleep duration will be calculated as the average time spent asleep each night (hours) and sleep regularity will be calculated as the standard deviation of nightly sleep durations (hours). Changes from baseline will be compared at week 4 and week 8.

Carotid to femoral pulse wave velocity (m/s) will be calculated using the Sphygmocor XCEL system. Changes from baseline will be compared at week 4 and week 8.

An end-diastolic gated B-Mode image of the common carotid artery will be recorded for 15 heart cycles using simultaneous 3-lead electrocardiogram and ultrasonography recording. The image will be evaluated using Carotid Studio Quipu Software to measure carotid artery intima-media thickness (mm). Changes from baseline will be compared at week 4 and week 8.

Femoral artery blood velocity and diameter will be continuously recorded using Doppler ultrasound for 1 minute at rest and during 1 minute of passive movement of the lower leg at the knee joint at a frequency of 1 hertz. Femoral artery blood flow will be calculated at baseline and during movement. The change in femoral artery blood flow will be calculated as peak blood flow during movement minus baseline blood flow. The change in femoral blood flow from baseline to peak is our assessment of femoral artery blood flow response to passive leg movement for which changes from baseline will be compared at week 4 and week 8.

Inclusion Criteria: Female Self-identified race is Black 18-30 years old Serum 25-hydroxyvitamin D concentration between 8-29.9 ng/ml determined at screening visit Exclusion Criteria: Unwilling or unable to give consent Unwilling or unable to undergo a venous blood draw Diagnosed with any chronic diseases or conditions including cardiometabolic diseases, cardiorespiratory diseases, chronic mental or psychological illness, musculoskeletal diseases/conditions, autoimmune diseases, cancer, gastrointestinal/malabsorption disorders, hyper-/hypocalcemia, hyper-/hypoparathyroidism, hyper-/hypothyroidism, kidney disease, or a history of kidney stones Taking medication that may influence blood pressure or blood vessel function Diagnosed with a sleep disorder (e.g., insomnia, restless leg syndrome, sleep apnea), or are at high risk for a sleep disorder according to the ISI (score >14) or STOP-bang (score ≥3) questionnaires Currently taking medications or supplements that affect sleep (e.g., Ambien, sedatives, melatonin, etc.) Currently working night-shift work Resting blood pressure >130 or >80 mmHg BMI >30 kg/m2 Currently pregnant, breast feeding, peri-menopausal, or post-menopausal Currently use tobacco (≥1 cigarette in the last month) Had COVID-19 in the past 60 days Received the COVID-19 vaccine or booster within in the past 14 days