A major research trial by the University of Auckland’s School of Population Health has found that taking higher doses of vitamin D once a month won’t lower your risk of heart disease.
The trial, led by the University’s Dr Robert Scragg, a professor of epidemiology, was conducted over three years using roughly 5,100 adults.
Previous studies have reported increased incidence of cardiovascular disease (CVD) among people with low levels of vitamin D. But earlier, randomised clinical trials of vitamin D supplementation have not found an effect, possibly because of using too low a dose of vitamin D.
The researchers tracked the heart health of roughly 5,100 adults aged between 50 and 84 from April 5, 2011, through November 6, 2012, with follow-ups until July 2015. The participants were mostly from family practices in Auckland.
About one-quarter were vitamin D deficient at the start of the trial - registering vitamin D levels of less than 50 nanomoles per litre via blood tests.
Half the group received a high-dose vitamin D supplement once a month, with an initial dose of 200,000 International Units (IUs). That was followed by a regular monthly dose of 100,000 IUs. The other half received a monthly regimen of placebo supplements.
The trial continued for more than three years, on average.
But in the end, nearly 12 percent of both groups had developed some form of heart disease, the researchers found.
And the risk for developing high blood pressure and/or experiencing a heart attack, stroke, heart failure or angina was more or less the same whether or not a participant had begun the study deficient in vitamin D.
The findings were published in the April 5 issue of JAMA Cardiology.
“While the findings rule out monthly dosing of the vitamin for preventing cardiovascular disease, the effects of daily or weekly dosing require further study,” Dr Scragg says.
“On-going research also will determine within the next three to four years whether vitamin D supplements prevent other diseases.”
The possibility that UV radiation, through a mechanism that involves vitamin D, may protect against cardiovascular disease was initially proposed in 1981. Results from recent meta-analyses have confirmed that people with low vitamin D status have increased risk of CVD.
The theory that vitamin D is protective against heart disease has been around since the 1980s. Natural sources of vitamin D include ultraviolet radiation from the sun and researchers noticed that the rates of cardiovascular disease were much higher in the winter when the body had lower levels of vitamin D.
Vitamin D is also found in foods such as fatty fish, fortified dairy and egg yolks.
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