Associations of Self-Reported Sun Exposure and 25- Hydroxyvitamin D with Blood Pressure: Cross-Sectional Analysis from a Multi-Ethnic Community Sample

Abstract Background : Physiological and epidemiological studies indicate that vitamin D may have several antihypertensive actions, and sun exposure is the primary source of vitamin D in humans. However, the results of recent trials are inconsistent. We carried out a cross-sectional analysis to evaluate the relationships between serum 25-hydroxyvitamin D [25(OH)D], sun exposure, and blood pressure (BP). Methods : We performed univariate and multivariable regression analyses. Sun exposure was assessed using a questionnaire to investigate the frequency of this activity in the past three months. Serum 25(OH)D was measured by liquid chromatography-tandem mass spectrometry from blood samples collected during baseline assessment. Systolic blood pressure (SBP) and diastolic blood pressure (DBP) were measured by an Omron T9P oscillometric device. Results : A total of 5,108 study participants aged 50–84 years were recruited from family practices in New Zealand. Age, ethnicity, BMI, and history of high BP were significantly associated with all BP indices. Serum 25(OH)D was not associated with systolic blood pressure (SBP) [25(OH)D <25 nmol/L mean diff -0.7 mmHg (1.5) compared to ≥75 nmol/L; P = 0.62] or diastolic blood pressure (DBP) [25(OH)D <25 nmol/L mean diff 0.7 (0.8) compared to ≥75 nmol/L; P = 0.79]. Sun exposure was positively associated ( P <0.0001) with serum 25(OHD) level. When all key variables were adjusted for, sun exposure was positively associated ( P < 0.05) with SBP [3.1 mmHg (1.0) compared to lowest; P = 0.01] and DBP [1.7 mmHg (0.5) compared to lowest; P = 0.01], but 25(OH)D was unrelated to these. Independently of sun exposure and 25(OH)D, BP varied with season, being lowest in summer (by up to 3 mmHg). Conclusion : These results indicate that sun exposure and winter season are associated with higher BP, independently of one another and of 25(OH)D, while the latter was unrelated to BP. The winter increase in BP is likely due to other factors than low vitamin D levels at that time of year (Figure 1).