NEW YORK (Reuters Health) - In older people with low vitamin D levels and a common type of high blood pressure, vitamin D supplements do not appear to lower blood pressure, according to a new study from the UK.
Among study participants who were at least 70 years old, researchers found that their blood pressure was unchanged after a year of heavy vitamin D supplementation.
"It doesn't look like - at the moment - (people) are going to be able to control their blood pressure with vitamin D supplements," Miles Witham, the study's lead author from the University of Dundee in Scotland, told Reuters Health.
"It's important that people who have high blood pressure go on taking their medications," he said.
Previous research has linked low vitamin D levels to high blood pressure, heart disease and even early death (see Reuters Health article of Nov 25, 2011 here: reut.rs/1a4Atg6.)
But few studies have looked at whether vitamin D supplements bring down blood pressure - especially in those with high isolated systolic blood pressure, which is when the top number of a blood pressure reading is greater than 140 millimeters of mercury (mmHg).
The U.S. Centers for Disease Control and Prevention says that systolic blood pressure should be below 120 mmHg and the diastolic pressure reading (the bottom number) should be less than 80 mmHg.
Healthy blood levels of the circulating form of vitamin D are thought to be about 30 nanograms/milliliter (ng/mL) or higher.
For the new study, Witham and his colleagues randomly assigned 159 people with high isolated systolic blood pressure and low vitamin D levels to one of two groups between June 2009 and May 2011.
While one group received 100,000 international units of vitamin D3 every three months for a year, the other group received a placebo pill.
Overall, the treatment group's vitamin D levels increased - from an average of 18 ng/mL to an average of 28 ng/mL, while the placebo group's remained low.
There were, however, no significant changes in blood pressure in either group. Participants' average blood pressure at the beginning and the end of study was 163/78 mmHg.
"It's a disappointing result," Witham said.
But not all hope for vitamin D may be lost, said Dr. Edward Giovannucci, who wrote a commentary accompanying the new study in JAMA Internal Medicine.
He told Reuters Health in an email that participants still had relatively high levels of vitamin D at the beginning of the study, which would decrease the chance of seeing a benefit from supplements.
"Thus, the potential benefit of vitamin D on blood pressure could depend on one's starting point," Giovannucci, a professor of nutrition and epidemiology from the Harvard School of Public Health in Boston, said.
Dr. James Vacek, who has studied vitamin D but wasn't involved in the new study, also said the finding doesn't close the door on potential benefits from the supplement.
"This is a specific study in a small group of patients who had longstanding high blood pressure," Vacek, a professor of medicine at the University of Kansas Hospital in Kansas City, said.
"Only depending on high-dose vitamin D to treat it wouldn't be appropriate," he added.
Witham said vitamin D may be more effective for lowering blood pressure for certain groups, such as diabetics, who have shown promising results in previous studies.
"There may be merit in doing other blood pressure trials, but perhaps we have to take a step back to look at what groups we want to lower blood pressure using vitamin D," he said.