It’s wintertime and that means cosy fires, country pubs and a lack of vitamin D, aka the ‘sunshine vitamin’.
It’s handed this bright and beautiful moniker because it’s the sole vitamin that’s produced when skin is directly exposed to sunlight or, more specifically, UVB (ultraviolet B) rays. In the summer, there should be sufficient hours of sunshine to stimulate your recommended daily amount. The same can’t be said for winter with shortened days and cloudier skies – especially around the time of the winter solstice. Which is a problem.
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“The more we learn about vitamin D, the more we realise how important it is,” says Dr Claire Pettitt, an expert dietitian and nutritionist. “It’s more classically known for its part in bone health, but it also plays a key role in immunity – it helps our bodies fight infections – and mood regulation, as low levels are linked to depression.”
As well as sunshine stimulation, you can source vitamin D from foods, including oily fish, eggs, liver, sun- exposed mushrooms and fortified options, like some fat spreads and breakfast cereals. The problem is it features in a small number of foods and in very small quantities, and is insufficient to deliver the NHS recommendation of 10 microgrammes (mcg) per day.
That’s why the NHS advises taking a vitamin D supplement from October to March. Pettitt agrees and directs you to vitamin D3, also known as cholecalciferol. “It’s the most effective form to increase your vitamin D levels because it’s the same form that we produce in our skin through sun exposure. That’s important, as many supplements are actually in the D2 form, which is less potent.”
This 10mcg figure is set in stone and doesn’t change as you age, though there is evidence that a vitamin D deficiency ages you. Research in the Journals of Gerontology in 2020 studied epigenetic patterns in 1,600 subjects and discovered that those with low vitamin D levels in their blood were biologically older than those who had adequate levels – also known as ‘age acceleration’.
So, the elixir of life is in vitamin D form, which you should enjoy with foods that contain fat as it’s a fat-soluble vitamin. But before you reach for the fun-sized packet of crisps, we’re talking the healthy fats found in avocados, nuts, seeds, eggs, salmon and mackerel.
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These supplements are affordable so, in theory, you’d think vitamin D deficiency was relatively rare. That’s not the experience of Pettitt.
“Vitamin D deficiency is actually quite common (between 25 and 58% of the UK population depending on which definition you use), even in the summer and, for some, even with a supplement. This is especially true if you’re someone who doesn’t spend a lot of time outdoors, like the elderly or those working long hours at a desk.
“Specific sectors of the population suffer from vitamin D deficiency, too. In the area of women’s health, those with polycystic ovary syndrome and infertility often record low levels. Individuals with gut disorders – e.g. those with coeliac disease or irritable bowel syndrome – might not absorb sufficient levels, either.”
Skin colour impacts the situation, too. According to a 2021 study in the journal Nutrients, African Americans have a 15–20-fold higher prevalence of severe vitamin-D deficiency due to melanin in the skin blocking the UVB solar radiation necessary for its synthesis.
Vitamin D deficiency has also been linked to fatigue and tiredness, muscle weakness and falls in the elderly, and bone-health issues, such as osteoporosis and osteomalacia. “It’s even been linked to an increased risk of chronic health issues like heart disease, diabetes and cancer,” Pettitt adds. “Ultimately, whatever population you sit in, you should have your levels checked regularly and supplement accordingly.”
And that’s not solely in search of a deficit. “The upper limit for vitamin D intake is 100mcg for adults, which means taking more than that may be harmful,” says Pettitt. “If you take too much vitamin D, so that it increases the amount in your blood to pretty high levels, you may experience nausea, vomiting, confusion, pain, loss of appetite or excessive thirst or urination, even kidney stones and kidney failure. To reiterate, have your blood tested and then, ideally, discuss what dose of vitamin D supplementation you should be taking with a healthcare practitioner.”
Colds and flu affect around 15 million people in the UK each year and are much more common in the winter. Supplementing with vitamin D might not be a bulletproof option to prevent illness but there’s clear evidence it bolsters your immune system. Either that or head to sunnier climes. Now there’s a thought…
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