"Vitamin D can produce 'amazing' improvements in heart function," claims The Independent about the results of a recent study, while BBC News reported suggestions the results were "stunning".
However, the study in question, which involved giving people with heart failure vitamin D supplements, did not result in better exercise capability.
Heart failure is caused by the heart failing to pump enough blood around the body at the right pressure. Your heart doesn't stop, but fails to work properly, causing symptoms of breathlessness, tiredness and ankle swelling.
Many people with the condition are also vitamin D deficient, prompting Leeds-based researchers to study whether vitamin D supplements might help the condition.
The study involved 229 participants who were randomised to receive either a daily high-dose vitamin D supplement for a year or a placebo.
People in the vitamin D group showed encouraging improvements in measures of left ventricular function, a gauge of how well blood is pumped from the heart with each heartbeat.
But the study was unable to show any vitamin D-related improvements in the main symptoms of heart failure, and showed no improvement in walking distance.
Given that backdrop, it's a stretch to describe the hearts as "healed" – or call the results "stunning". Still, these are early days. Larger and longer-term studies may find out whether these heart changes improve the main symptoms of the condition over time.
Where did the story come from?
The study was carried out by researchers from the University of Leeds and Leeds Teaching Hospitals NHS Trust, and was funded by the Medical Research Council UK.
It was published in the peer-reviewed Journal of the American College of Cardiology.
Generally, the media reported the story accurately, though the implications of the research were arguably overhyped, possibly driven by the enthusiasm of the lead researcher in describing his team's work.
The BBC did provide a more sober note of caution, however, quoting Professor Peter Weissberg of the British Heart Foundation, who cautioned: "the patients seemed no better at exercise.
"A much bigger study over a longer period of time is now needed to determine whether these changes in cardiac function can translate into fewer symptoms and longer lives for heart failure patients."
What kind of research was this?
This was a double-blind randomised controlled trial (RCT) looking to see whether vitamin D3 supplements could help people with chronic heart failure.
People with heart failure are often older and can be vitamin D deficient, possibly the result of not getting enough sunlight, which stimulates vitamin D production in your skin.
The researchers wanted to see if boosting patients' vitamin D levels would help with the condition, which causes breathlessness, excess tiredness and swollen ankles.
An RCT is the best study design to find out whether vitamin D3 supplements improve chronic heart failure. The only way they can be improved is to make them larger or longer, or to pool the results of many RCTs investigating the same thing, called a meta-analysis.
What did the research involve?
The research recruited 223 mostly male vitamin D-deficient adults with chronic heart failure caused by left ventricular systolic dysfunction – meaning the main pumping chamber of the heart on the left side wasn't working properly.
The researchers randomised half of the participants to take 100 micrograms of vitamin D3 supplements daily for a year, and half to take a placebo. The main measure of potential improvement was the distance the men could walk in six minutes.
A secondary measure was changes in their heart function, measured as the proportion of blood pumped from the heart – specifically, the left ventricle – on a heart scan, called the ejection fraction.
Changes in the size of the left ventricle were also monitored, although only 34 people had the two scans necessary to monitor change.
Neither the men nor those assessing their hearts or exercise for changes knew if they'd taken the placebo or vitamin D – a so-called double blind study.
The year-long study was completed by 163 people. The rest withdrew (23), died or deteriorated (28), or suffered side effects (5).
What were the basic results?
Despite excitable headlines, the main measure of interest – the distance the participants could walk in six minutes – did not improve using vitamin D3. In fact, it was about 13 metres worse after a year.
Those in the placebo group actually walked an average of 10 metres more after a year. But the differences between placebo and vitamin D were small enough that effectively it meant they were no different from one another.
The finding that hit the headlines was a secondary measure of heart function, which improved more in people using vitamin D3 than those using a placebo, who also improved a little.
People using vitamin D improved their ejection fraction by 7.65%, from 25.6% to 33.25% over one year, while those on placebo improved by 1.36%, from 26.5% to 27.86%. Other significant changes were also seen for measures of how well the left ventricle was functioning.
No safety concerns or side effects seemed apparent in those using vitamin D3 supplements for the year.
How did the researchers interpret the results?
The researchers concluded: "One year of 100 micrograms daily 25-OH vitamin D3 supplementation does not improve six-minute walk distance, but has beneficial effects on LV [left ventricular] structure and function in patients on contemporary optimal medical therapy. Further studies are necessary to determine whether these translate to improvements in outcomes."
They added: "New therapies for serious chronic conditions, including CHF [chronic heart failure], are often expensive, increasingly technical and frequently fail to meet the rigorous demands of large phase 3 clinical trials.
"Vitamin D might be a cheap and safe additional option for CHF patients and may have beneficial effects on multiple features of the syndrome."
This study showed that taking daily vitamin D3 supplements for a year did not improve the ability of people with chronic heart failure to walk further, but did improve elements of their heart function.
The study was well designed, but larger studies are needed to confirm the findings more definitively.
The main limitations of the research include the fact the main focus was on men, its relatively small size, and an absence of measures relating to the main symptoms of the condition.
The study was not able to tell us whether the heart change improvements seen enhanced quality of life in terms of breathlessness, tiredness and swollen ankles. There were no improvements seen in walking distance.
If you think you may be vitamin D deficient, talk to your doctor about whether supplements may help, or whether getting more sunlight may be an equally effective and more attractive approach.
If you take vitamin D supplements, do not take more than 25 micrograms (0.025mg) a day, as it could be harmful, though taking less than this is unlikely to cause any harm.