Taking higher-than-recommended doses of vitamin D may reduce the risk of atrial fibrillation in older adults, according to Finnish researchers who say theirs is the first randomised controlled trial to make this observation.
People who were given 40 µg/day of vitamin D3 had a 27% lower risk of atrial fibrillation – a known risk factor for stroke and heart failure – than those who received a placebo, while those who were given 80 µg/day had a 32% lower risk, the study, published in the American Heart Journal, found.
For reference, the European Food Safety Authority (EFSA) recommends 15 µg/day of vitamin D for adults, while the NHS recommends just 10 µg/day.
On its website, the NHS warns: “Do not take more than 100 micrograms (4,000 IU) of vitamin D a day as it could be harmful.” It adds that taking too much vitamin D can cause hypercalcaemia, which in turn can weaken bones and damage the kidneys and heart.
However, consultant nutritionist Dr Carrie Ruxton, from Nutrition Communications, said the doses used in the study were within safe limits.
She told Vitafoods Insights: “While some may baulk at the higher doses of vitamin D used in this study, they aren’t excessive because the safe upper level set by EFSA is 100 µg/day.
“Not only this – research from Professor Kevin Cashman at the University of Cork has shown that intakes of around 30 µg/day are needed to establish optimal blood levels of vitamin D in northern European populations due to their lack of sun exposure.
“More than 90% of vitamin D in the body comes from sunlight rather than the diet, and few foods are naturally rich in vitamin D – oily fish and eggs being the best examples. So, overall, I’m not worried about people taking up to 100 µg/day of vitamin D if they need it.”
The Finnish Vitamin D Trial (FIND) was designed to explore the associations of vitamin D supplementation with the incidence of cardiovascular diseases and cancers.
Almost 2,500 participants, all of whom were aged over 60, were randomised into three groups: one placebo group, one group supplemented with vitamin D3 at 40 µg/day (1600 IU), and a third group supplemented with 80 µg/day (3200 IU). All participants were also allowed to take a personal vitamin D supplement of up to 20 µg (800 IU) per day.
At baseline, none had been diagnosed with cardiovascular disease or cancer. However, over the five-year study duration, 190 people were diagnosed with atrial fibrillation: 76 in the placebo group, 59 in the 40 µg group, and 55 in the 80 µg group.
Ruxton said: “We often think of populations in higher-income countries as over-nourished and suffering high levels of obesity but, despite this, vitamin D deficiency is common.
“Current recommendations for vitamin D are typically all about bone health and aim to provide enough vitamin D in the blood to guard against bone loss and osteoporosis. But this doesn’t reflect the benefits of vitamin D for other conditions or parts of the body, such as immunity or heart health, which are still emerging topics for vitamin research.
“In the new study, Finnish researchers used existing data to assess two levels of vitamin D supplementation – 40 µg/day or 80 µg/day – versus a placebo. They found that both intakes of vitamin D significantly reduced the risk of atrial fibrillation – a risk factor for heart attack.”
According to the researchers, FIND is the first randomised controlled trial to observe that vitamin D supplementation reduces the risk of atrial fibrillation – the most common type of cardiac arrhythmia – in healthy men and women.
The trial, which was conducted at the University of Eastern Finland, has previously published studies showing no association with the incidence of other cardiovascular events or cancers.
However, Ruxton urged against reading too much into the most recent findings.
“It’s worth pointing out that the Finnish study was not designed to test the effects of vitamin D on atrial fibrillation – this was an analysis of an existing dataset,” she said.
“The researchers admitted they don’t know why vitamin D would protect the heart, so we definitely need to repeat this research in another group of adults and establish likely mechanisms of action before we encourage people to start taking vitamin D for their heart health.”
