Vitamin D and blood pressure

Abstract

The physiological function of circulating 25-hydroxyvitamin D (25(OH)D) is to maintain serum calcium range that supports skeletal system. Evidence is mounting that vitamin D has beneficial effects on other important functions in tissues not primarily related to mineral metabolism. Circulating 25(OH)D levels are influenced both by the amount of ultraviolet B exposure from the sun to the skin and dietary intake.

The aims of this thesis were to: 1) examine the predictors of serum 25(OH)D levels both during winter and summer among women from the Swedish Mammography Cohort (SMC) in central Sweden (latitude 60° N). 2) evaluate the association between plasma 25(OH)D levels and the prevalence of hypertension among men in the Uppsala Longitudinal Study of Adult Men (ULSAM). 3) evaluate the association between serum vitamin D levels and blood pressure among women in the SMC. 4) quantitatively summarize the evidence from published studies on the association between circulating 25(OH)D and hypertension.

In 116 women (61-86 years), investigated regarding determinants of serum 25(OH)D concentrations during winter, mean concentrations were 69 nmol/L. In a multiple linear regression model serum 25(OH)D concentrations were associated with dietary vitamin D, travel to sunny location during winter and the use of dietary supplements. Among these women 100 participated again in an examination during late summer and their mean concentrations were then 99 nmol/L. Determinants of serum 25(OH)D concentration during summer were baseline serum 25(OH)D concentration during winter, sun habits, body mass index and skin type.

From the ULSAM 833 men aged 71 ±0.6 years had mean plasma 25(OH)D concentrations of 69 nmol/L. They were examined in a cross-sectional study to determine the association between plasma 25(OH)D concentrations and the prevalence of hypertension. In a multivariable adjusted logistic regression model, men with plasma 25(OH)D concentrations <37.5 nmol/L had a 3-fold higher prevalence (OR=3.3 (95% CI:1.0–11.0)) of hypertension compared to those with ≥37.5 nmol/L.

In a sub-group from SMC 550 women, aged 59-85 years had serum 25(OH)D concentration mean of 79 nmol/L. The women were examined using a simultaneous quantile regression model to estimate differences in percentiles of systolic, diastolic, mean arterial and pulse pressure in relation to serum 25(OH)D status. The multivariable adjusted statistically significantly difference in pulse pressure for the group of women with low serum levels of 25(OH)D (<50 nmol/L) compared with high (≥100 nmol/L) was 7.2 mmHg (95% CI: 2.5-11.9) within the 25th percentile of pulse pressure.

For the meta-analysis study-specific results were combined using a random-effects model. The summary odds ratios (95% CI) for hypertension comparing the highest versus the lowest circulating 25(OH)D concentrations were 0.73 (0.63-0.84), and 0.84 (0.78-0.90) for 40 nmol/L increment in the dose-response meta-analysis.

In conclusion, dietary vitamin D, travel to sunny location and the use of dietary supplements during winter seems to affect serum 25(OH)D concentrations and sun habits, body mass index and skin type during summer. Findings indicate that circulating 25(OH)D concentrations are associated with hypertension and pulse pressure.