Hypertension is one of the world’s top causes of death, with approximately 1 billion people worldwide suffering from the condition.
While several studies have found a positive correlation between hypertension and vitamin D deficiency, the effects of vitamin D intake on blood pressure and hypertension have not yet been proven.
With this in mind, researchers from Iran’s Hamadan University of Medical Sciences conducted a case-control study to investigate the potential impact of vitamin D levels on hypertension risk and blood pressure.
High blood pressure, low vitamin D levels
They assessed a total of 188 subjects (55 hypertension patients and 133 healthy controls) aged 25 to 89; 139 were women and 49 were men.
Their medical history was recorded and they underwent a physical examination, after which their blood levels of serum vitamin D were measured.
The researchers found that those with hypertension had lower serum levels of vitamin D than the healthy controls: "Mean and standard deviation of serum 25(OH)D level in patients suffering from hypertension was 13.10±9.7 ng/ml and in control group was 20.87±10.34 ng/ml. This variance was statistically significant."
They added that systolic and diastolic blood pressure, as well as mean arterial blood pressure, was higher among those deficient in vitamin D than in those with sufficient vitamin D levels.
Age and gender stratification
After adjusting for gender, there remained a 'significant relationship' between serum vitamin D levels and blood pressure in both males and females.
A similar relationship was observed after adjusting for age, but only in those under 50; those above 50 did not display a statistically significant correlation between vitamin D levels and blood pressure.
This led the researchers to state that "unknown factors may play a role on relation between serum vitamin D and blood pressure levels, especially in old age".
Possibilities and limitations
The study said the role of vitamin D supplementation in preventing or treating hypertension was 'controversial', despite previous research having concluded that vitamin D levels have an inverse association with blood pressure.
Alluding to earlier studies that had reported lowered systolic blood pressure in hypertension patients following calcitriol supplementation, as well as vitamin D indirectly lowering blood pressure by playing a part in parathyroid hormone performance, the researchers said that "further studies with more samples are required, in which all possible factors are taken into account".
They also acknowledged the study's limitations regarding sample size and a disproportionate ratio of female to male subjects, as well as their use of a convenient sampling method to collect data.
In light of the considerable difference in serum vitamin D levels between the study's hypertensive participants and the healthy controls, they concluded that "serum 25(OH)D is inversely associated with blood pressure, so recognising people with vitamin D deficiency is imperative".
Source: Journal of Clinical and Diagnostic Research
"Evaluation of the Relationship between Serum 25-Hydroxy Vitamin D and Hypertension in Hamadan, Iran-A Case Control Study"
Authors: Behshad Naghshtabrizi, et al.