A new study found that low vitamin D status was associated with the onset of orthostatic hypotension events over 4.4 years of follow up, particularly among women.
Orthostatic hypotension (OH), also known as postural hypotension, describes low blood pressure that results from suddenly standing up or stretching. The symptoms may include feeling dizzy, lightheaded or even loss of consciousness. OH is often mild (putting your head down between your legs often cures it); although, long-lasting OH can be a sign of a more serious underlying problem. OH affects approximately 20% of people over the age of 65 and 30% of people over the age of 75.
Past research has found that vitamin D likely plays a role in cardiovascular health due to the presence of vitamin D receptors in endothelial cells. Furthermore, some studies have discovered that vitamin D supplementation may help reduce blood pressure.
These findings have led researchers to try to understand the relationship between vitamin D status and OH. The current available studies on this topic have been limited to mostly cross-sectional studies, which are relatively weak. A cross-sectional study merely assesses the relationship between an outcome (i.e. OH) and an exposure (i.e. vitamin D levels). Longitudinal studies are stronger, because researchers conduct several observations of the same subjects over a period of time. Nonetheless, cross-sectional studies continue to report an association between low vitamin D levels and OH.
A randomized controlled trial also evaluated the effects of vitamin D supplementation on OH, concluding that there were no benefits associated with supplementation. However, the RCT used intermittent dosing of 100,000 IU every three months for a year. If you follow the Vitamin D Council, you likely already know that studies that use such infrequent bolus dosing rarely produces positive results. Therefore, we are left still questioning the role that vitamin D plays in OH.
In an effort to clarify the relationship between OH and vitamin D, researchers measured the vitamin D levels of 1,308 elderly individuals at baseline and recorded the onset of OH over an average duration of 4.4 years.
Trained nurses assessed the development of OH by measuring blood pressure while sitting and lying down. Orthostatic blood pressure was then measured after 1 and 3 minutes of standing. OH was defined as a large drop in blood pressure within three minutes of standing up (drop of <20 mm Hg in systolic blood pressure or <10 mm Hg in diastolic blood pressure).
Here is what the researchers found:
- Over the 4.4-year follow-up, 463 people developed OH.
- Those with OH at follow-up had significantly lower baseline vitamin D status than those without (p < 0.001).
- After adjusting for potential confounding factors, those with the lowest vitamin D levels (<6 ng/ml for men or <16.8 ng/ml for women) developed OH 1.18 times more often comparison than those with the highest vitamin D levels (56.8 ng/ml in men or 36.8 ng/ml).
- When the researchers stratified the results by gender, they found that the association between baseline vitamin D and the onset of OH was not significant among men.
- In women, the association between vitamin D and the onset of OH was significant. Women with the lowest vitamin D levels developed OH 1.36 times more than women with the highest vitamin D levels over the 4.4 years.
The researchers summarized the results,
“In conclusion, hypovitaminosis D predicts the onset of orthostatic hypotension, independently of potential con-founders, in a large representative cohort of older men and women.”
The study provides some clarity upon the relationship between vitamin D and OH. Although, it leaves us to question why low vitamin D levels are only significantly associated to hypotension among women. The researchers proposed a possible explanation, stating that their study may have not included enough men, which would mean the study would lack the power needed to determine the relationship between OH and vitamin D in men. They stated that their analyses included three times as many women as it did men.
The researchers pointed out a few of the study’s limitations. The study did not measure vitamin D levels after the follow-up, meaning that the vitamin D levels may have changed within this time frame. Furthermore, the study consisted of a relatively short follow up period.
On the other hand, the researchers gathered a large amount of data from all participants, allowing them to adjust their findings for various confounding factors. These confounding factors included age, body mass index, activities of daily living, medications, smoking habits and medical conditions, among many others. This allowed the researchers to better isolate the relationship between vitamin D and OH.
Randomized controlled trials that use daily adequate doses are required to assess the effects of vitamin D supplementation in the elderly with OH.
Tovey, A & Cannell, JJ. Low vitamin D status predicts the onset of orthostatic hypotension, according to new study. The Vitamin D Council Blog & Newsletter, 2016.