What a summer we’ve had, with temperatures soaring to 40.3C, the hottest on record in the UK. Alas, though the sky outside is powder blue as I write this, and my walk on Lyth hill this morning was as warm as it was beautiful, Autumn is here.. you know… the smell of damper air, the changing colours of landscape where vibrant greens give way to gentler shades of orange and gold, and everything seems a wee bit wistful. Of course, autumn is also the season of harvest when we see combine harvesters a plenty in the fields and tractors bustling down our roads seemingly from dawn ‘til dusk. It’s also a time to look forward to a bounty of new produce – think squashes, aubergines, apples, pears, beetroot, parsnips, and wild mushrooms.
Autumn also ushers in a decline in sunshine hours and in the sun’s potency, which in turn affects our vitamin D levels. That’s because vitamin D (which, doesn’t really deserve its vitamin categorisation, as it’s more like a hormone) is mostly obtained from the sun. We synthesize around 90% from sunlight when it touches our skin; the remaining 10% is sourced from food. But, like most things scientific, it’s a bit more complicated than that!
I should say at this point that if you want to skip over the next few paragraphs and cut to the key messages, drop down to the bottom of the page and have a look at “3 THINGS.” Otherwise, I hope you enjoy reading on and learn a little more about vitamin D and its impact on health.
Vitamin D comes in two forms: D2 (aka ergocalciferol) from plants, and D3 (aka cholecalciferol), from animals. Both perform the same function in the body, so you don’t need to worry about the type, except perhaps that D3 is more potent than D2. The vitamin D you get, or rather that you make from sunshine, is vitamin D3, and it can only be synthesized when the sun’s UV-B levels are between 290-320nm. In the UK, the sun isn’t powerful enough to trigger synthesis between October and March, so we must rely on vitamin D from dietary sources or from stores in our adipose tissue built up over the summer or take dietary supplements. More on this later.
Maybe now is a good time to introduce what vitamin D actually does for your body. Primarily, it enables you to absorb and regulate calcium and phosphorous. These nutrients are important to form and maintain healthy bones, teeth, and muscles. If your vitamin D levels are low, you’re at greater risk of developing osteomalacia (soft/weak bones) and osteoporosis, especially if the deficiency persists. In children, deficiency causes rickets, a disease characterised by bone pain and bone deformities. While rickets might seem like an archaic disease, it is in fact on the rise in the UK, perhaps because children tend to spend more of their free time indoors. Although the main link between vitamin D and health relates to bone health, there’s increasing evidence that vitamin D plays a role in immune function. Several studies have highlighted that it protects against respiratory infections like flu and Covid 19, though it’s fair to say that evidence is patchy. With regard to immune function, low levels of vitamin D have been correlated with an increased risk of developing autoimmune conditions such as rheumatoid arthritis, type 1 diabetes, asthma and inflammatory bowel disease. Vitamin D insufficiency has also been linked with cardiovascular diseases including elevated blood pressure, heart failure and stroke.
Vitamin D deficiency is in fact one of the most common deficiencies worldwide, second only to iron deficiency. According to the National Diet and Nutrition Survey (NDNS), 1 in 6 adults in the UK aren’t getting enough vitamin D, with young women, children, older people and people with darker skin at heightened risk of deficiency. So how do you know if you’re getting enough? Well, unless you have a blood test, you don’t really! But there are one or two things you can do to make sure you’re getting the right amount. Firstly, skin exposure. Daily skin exposure (as a rule of thumb, a third of your body should be exposed) in the summer, of around 10-15 minutes if you have light skin, or 25-40 mins if you have darker skin, around the middle of the day, should provide you with all the vitamin D you need. However, because synthesis through sunlight isn’t possible during winter, the government recommends a daily 10 microgram supplement for adults between October and March. Following these simple steps should help to ensure you’re getting adequate amounts of vitamin D and of course you can top up from dietary sources (oily fish is the best source, but you can find vitamin D in eggs, meat, dairy, mushrooms and in fortified products like cereals, juices, milk and fat spreads). However, just in case you’re curious or concerned, here are some things to look out for that can point to insufficiency/deficiency: fatigue, muscle aches and pains, low immune health, hair loss, broken bones or stress fractures, anxiety or depression.
Before signing off this article, there’s a couple of cautionary notes to sound. Thankfully, getting too much vitamin D from sunlight isn’t possible, thanks to a natty little mechanism our bodies have developed for capping the amount of vitamin D you’re able to synthesize. However, overexposing your skin to sun can of course have negative health consequences. These include sunburn, skin ageing and increasing your risk of developing skin cancer. Additionally, while overdosing on vitamin D from sunlight or food isn’t possible (there just isn’t enough in food!), the same can’t be said of dietary supplements, so it’s important to stick to recommended doses (10 micrograms, though additional guidance available states that people should not exceed 100 micrograms a day) as high levels of vitamin D can be harmful.
Sadly, like summer, my blogging has now to come to an end as I embark on my final year of university. Thank you, Wendy Joelson, for giving me the opportunity to share some learnings from the fascinating world of nutrition. Most of all, thank you for taking time to read these posts. I hope you’ve found them interesting and useful.
Wishing you good health,
Jools
TOP 3 THINGS YOU SHOULD KNOW ABOUT VITAMIN D
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Vitamin D is essential for bone health. It also plays an important part in immune function, and is thought to minimize the instances and effects of respiratory infections. |
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90% of your vitamin D intake comes from summer sunlight exposure. For people with light skin, 10-15mins in the sun should meet their vitamin D needs, while people with darker skin should spend around 25-40 mins. Only 10% of your vitamin D intake comes from food (oily fish, liver, egg yolk, red meat, mushrooms and fortified foods). |
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When the sun’s UVB isn’t strong enough to facilitate vitamin D synthesis (between October and March), it is recommended that you take a vitamin D supplement of 10 micrograms per day.
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