PROGRAM | Applied Physiology

By: Michele D’Agata Chair: Melissa Witman

ABSTRACT

Cardiovascular diseases (CVD) are the leading cause of death among women in the United States. However, CVD prevalence is about 15 percent higher in non-Hispanic Black women (BLW) compared with women of other races and ethnicities. Vitamin D insufficiency and deficiency, defined as serum 25-hydroxyvitamin D concentrations ([25(OH)D]) < 30 ng/ml and < 20 ng/ml respectively, affect an estimated 92 percent of BLW due to increased melanin pigment in the skin and low dietary consumption of vitamin D. Low serum [25(OH)D] is associated with increased CVD mortality, although the mechanisms are unclear. Vitamin D deficiency has been separately associated with several independent risk factors for CVD including non-dipping nocturnal blood pressure (BP) and poor sleep health, both of which disproportionately affect BLW compared with women of other races. Moreover, these identified racial disparities in CVD risk factors begin to arise as early as young adulthood, marking this as a critical time point for altering the trajectory of CVD risk among BLW. However, the effect of serum [25(OH)D] on nocturnal BP dipping and sleep health metrics has not yet been evaluated in young adult BLW. Purpose: To compare 1A) nocturnal BP dipping and 2A) device-estimated sleep health metrics between young adult BLW with serum [25(OH)D] < 30 ng/ml versus serum [25(OH)D] ≥ 30 ng/ml, and to determine if increasing serum [25(OH)D] in BLW with serum [25(OH)D] < 30 ng/ml via 8 weeks of daily oral vitamin D3 supplementation with 5,000 IU/day has an effect on 1B) nocturnal BP dipping and 2B) device-estimated sleep health metrics. Hypotheses: 1A) systolic and diastolic BP dipping and 2A) device-estimated habitual sleep duration and sleep efficiency would be lower in BLW with serum [25(OH)D] < 30 ng/ml versus serum [25(OH)D] ≥ 30 ng/ml. Eight weeks of daily oral vitamin D3 supplementation would significantly increase serum [25(OH)D] to sufficient concentrations and 1B) increase systolic and diastolic BP dipping % and 2B) increase sleep duration and sleep efficiency in BLW with baseline serum [25(OH)D] < 30 ng/ml. Cross-Sectional Methods: Participants included generally healthy, non-hypertensive, non-obese, non-shift working, 18-30-year-old BLW who were free of evidence of clinical sleep disorders. Fasted venous blood sampling was performed for the clinical assessment of serum [25(OH)D], followed by 24-hour ambulatory blood pressure monitoring (ABPM) to evaluate nocturnal BP dipping (N=42; N=30 with serum [25(OH)D] < 30 ng/ml, N=12 with serum [25(OH)D] ≥ 30 ng/ml) and 14 days of wrist actigraphy to evaluate habitual sleep duration and sleep efficiency (N=43; N=31 with serum [25(OH)D] < 30 ng/ml, N=12 with serum [25(OH)D] ≥ 30 ng/ml). Intervention Methods: Following baseline measurements, a subset of participants with serum [25(OH)D] < 30 ng/ml underwent daily oral vitamin D3 supplementation for 8 weeks and repeated blood sampling (N=14), ABPM (N=13), and sleep monitoring (N=14) at or immediately prior to week 8 of the intervention period. Cross-Sectional Results: Serum [25(OH)D] was significantly different between groups at baseline (17.1±6.9 vs. 39.9±8.2, ng/ml; P<0.001). Nocturnal systolic (10.6±5.0 vs. 10.2±6.0, %; P=0.81) and diastolic (15.8±6.3 vs. 17.7±8.3, %; P=0.42) BP dipping were not different between BLW with serum [25(OH)D] < 30 ng/ml vs. ≥ 30 ng/ml, respectively. Sleep duration was not different between BLW with serum [25(OH)D] < 30 ng/ml (6.6±0.8, hours) vs. ≥ 30 ng/ml (6.9±0.8, hours) (P=0.28). However, sleep efficiency was significantly lower among BLW with serum [25(OH)D] < 30 ng/ml (80.4±3.9, %) vs. ≥ 30 ng/ml (84.0±4.3, %) (P=0.01). Intervention Results: Compared to baseline, participants that underwent oral vitamin D3 supplementation experienced a significant increase in serum [25(OH)D] at week 8 (17.2±7.3 vs. 55.1±9.2, ng/ml; P<0.001). However, no changes were observed for systolic (10.9±4.3 vs. 11.4±4.0, %; P=0.74) or diastolic (16.2±6.8 vs. 16.1±8.1, %; P=0.98) BP dipping from baseline to week 8, nor sleep duration (6.3±0.9 vs. 6.3±0.9, hours; P=0.79) or sleep efficiency (80.2±4.0 vs. 80.9±4.3, %; P=0.56) from baseline to week 8, respectively. Conclusions: Participants with vitamin D insufficiency/ deficiency had significantly lower sleep efficiency compared with participants with vitamin D sufficiency, although no differences were observed between groups for sleep duration or nocturnal BP dipping. Further, findings do not indicate a beneficial effect of vitamin D supplementation on nocturnal BP dipping or device-estimated habitual sleep health metrics in young, otherwise healthy BLW.

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