Some clinicians currently recommend vitamin D supplementation to treat cases of high blood pressure.
"It hasn't been clear though whether giving vitamin D to people actually lowers their blood pressure as individual trials have been too small to find out the answer."
Vitamin D is used in the body to regulate calcium and phosphorus absorption and to maintain healthy bones and teeth. It is also believed to reduce the risk of several chronic diseases such as cancer, type 1 diabetes and multiple sclerosis.
Most of the body's vitamin D supply comes from exposure to the sun. Sensible sun exposure on bare skin for 5-10 minutes two or three times a week is believed to be enough to allow the body to produce sufficient amounts of the vitamin.
While sunlight is both its most common and most efficient source, vitamin D can also be obtained from various food sources - most notably fish oil and fatty fish.
A number of intervention studies have been conducted to investigate the blood-pressure-lowering qualities of vitamin D as low levels of vitamin D are associated with elevated blood pressure. These studies have so far provided conflicting evidence as to the effects of vitamin D on cardiovascular health, however, driving the need for a systematic review.
Results show supplements 'do not lower your blood pressure'
Collaborators from the UK, US, Australia, New Zealand, India and Europe worked together to analyze trial and patient data, including data from 46 trials where vitamin D had been used in attempt to lower blood pressure (involving 4,541 participants in total). Individual patient data were obtained for 27 trials (involving 3,092 participants).
Data for vitamin D levels, systolic and diastolic blood pressure, changes in blood pressure over time and participant demographics were extracted for analysis by the researchers.
"By combining all of these trials into one analysis, we have been able to show that taking vitamin D supplements doesn't lower your blood pressure - even if you start with low vitamin D levels or a high blood pressure," states Dr. Witham.
Dr. Witham believes that the study's findings are important as many clinicians have already recommended that patients with hypertension should take vitamin D. "Our work shows that this doesn't work," he explains, "and so vitamin D cannot be recommended as a way to help control high blood pressure."
"Vitamin D can help reduce falls and fractures in older people, and might still have other health benefits," he adds, "but we need to wait for the results from further large clinical trials before we know if more widespread use of this medication is safe or worthwhile."
While medication can be prescribed to control and prevent high blood pressure, there are also a number of lifestyle changes that can be made, rather than relying on ineffective vitamin D supplementation. Eating healthy foods, decreasing salt consumption, limiting alcohol, reducing stress and quitting smoking - all of these measures are recommended for lowering blood pressure.
Previously, Medical News Today reported on a study that associated low levels of vitamin D with a greater risk of seasonal affective disorder.