Vitamin D, the sunshine vitamin, is in the spotlight again after a study of Covid-19 patients admitted to a hospital in Barcelona found that giving high doses of the vitamin early in treatment could cut deaths by 60 per cent.

Scientists from the University of Barcelona showed that patients prescribed calcifediol – an intensive dose of Vitamin D usually used for people with chronic kidney failure – were also less likely to be admitted into intensive care.

The vitamin D debate has been rumbling on since the beginning of the pandemic, when studies started to suggest that its deficiency may worsen Covid symptoms.

Late last year some 200 public figures and doctors signed a letter calling for the British Government and health bodies to recommend to adults a daily vitamin D intake of 4000 IU. More of us are already taking it in supplement form, an eight per cent increase since last March, according to Mintel, and no wonder. Aside from the fact it has been in the headlines and the topic of much scientific and political talk, it’s essential for bone and muscle health and immune system function.

Even if scientists are divided over how much of a wonder vitamin it is, most experts agree that a daily dose is useful for overall health at least. "I have been a fan of vitamin D for many years," says Dr Sarah Jarvis, GP and clinical director of patientaccess.com. "I recommend to my patients that they all consider taking it." Its role in bone health is well known, but low levels are also associated with an increased risk of respiratory diseases, including asthma, and its deficiency has been linked to reduced lung function, which can affect the ability to fight respiratory infections.

Dr Jenna Macciochi, lecturer in immunology at the University of Sussex, and author of Immunity: The Science of Staying Well, says: "Vitamin D is different from the other vitamins because it’s actually a steroid hormone and it controls over 100 different genes in our body. It’s doing a lot. We call it an essential vitamin because if we don’t have it, we start to see problems."

One recent Danish study into the benefits of vitamin D claimed that women who spent more than 20 years working outdoors decrease their chance of developing breast cancer by 17 per cent after they turn 50. But, says Dr Michelle Harvie, research dietitian for Prevent Breast Cancer, that study doesn’t offer conclusive proof. "It is true that people with lower vitamin D tend to get more breast cancer, [but] there’s no really great evidence for me to say if you take a vitamin D supplement it will stop you getting the disease," she says.

Scientific rigour entails proving cause and effect. "The best way to prove this would be to see if we give someone vitamin D, do they get less breast cancer?" says Dr Harvie.

Yet, she notes, "a few years ago a large US research study called VITAL, of over 25,000 men aged 50+ and women aged 55+ was published that reported that taking vitamin D didn’t prevent people getting cancers, but did make them 17 per cent less likely to get advanced fatal cancers."

The VITAL study also looked at whether we need more vitamin D for optimal heart health than we require for bone health. Its lead author concluded, "The answer, based on available research, seems to be no." In June 2019, its findings were part of a review, published in JAMA Cardiology, of 21 clinical trials, which showed that vitamin D supplements don’t reduce the risk of either suffering or dying from a heart attack or stroke.

Tracy Parker, senior dietitian at the British Heart Foundation, also urges caution when looking at top-line research, pointing at a 2015 Scottish study part-funded by the BHF.

"[It] showed that, although having low levels of vitamin D is associated with increased risk of cardiovascular disease, the low vitamin D is a result of lifestyle factors that increase your risk of heart disease and stroke, rather than being the cause of increased risk itself."

Nonetheless, vitamin D has enough proven benefits that we need to ensure we get enough. So how? Our bodies create vitamin D from direct sunlight on the skin – and spending 20 minutes daily outside should mean most people get adequate levels.

But though vitamin D is found in oily fish, red meat, egg yolks and some fortified foods, it’s hard to get enough of it from food alone. Nor can you get vitamin D by sitting indoors by a sunny window, as glass blocks the UVB rays.

There’s a public health argument in favour of fortifying foods such as flour and milk, says Dr Macciochi, because it removes the need for people to remember to take supplements, or being able to afford them.

Meanwhile, Dr Jarvis advises those with a risk of deficiency take a supplement all year round. "The current recommendation is for 10 micrograms – 400IU. But my feeling is that’s pretty low. I take 800IU, 20 micrograms a day," she says.

It’s possible to overdose, but Dr Jarvis has never seen a case. "I’m far, far more likely to see people who are deficient," she adds.

"Plenty of people are at risk of deficiency," agrees Dr Macciochi. "People with darker skin, elderly people, people who are not getting out as much because of lockdown, or people who have a larger amount of body fat."

PHE notes that "too little vitamin D can lead to bone problems such as rickets in children, and bone pain and muscle weakness in adults, which may also increase the risk of falls in older people."

Perhaps our appreciation of this essential nutrient is here to stay.

The Daily Telegraph

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