Vitamin D has a knack for sounding like one of those dreary health admin tasks until autumn arrives, the sun disappears behind a ceiling of wet grey felt, and your body begins operating like a golf buggy with a fading battery.
For people in the UK, Dr Sarah Brewer, medical nutritionist, GP and Healthspan medical director, says the winter months can make getting enough of it rather less simple than standing near a window and hoping for the best.
Why Winter Makes Vitamin D Such A Fiddly Business
In theory, the arrangement is elegant. Sunlight hits the skin, the body gets to work, and vitamin D production begins. In practice, Britain has weather, cloud, latitude, jumpers, office hours and a national talent for pretending March is spring when it is plainly still doing an impression of November.
Dr Brewer puts the seasonal problem plainly:
“You can make vitamin D in your skin when the UV index is greater than 3. As a result, vitamin D levels tend to plummet during autumn and winter in people living in northern latitudes such as the UK. Food sources then become important, but if you don’t eat much oily fish, liver products, eggs, butter or fortified foods, you are likely to remain deficient during winter.
That is the nub of it. During brighter months, the skin can play its part. During the darker stretch, diet matters more — and not everyone is breakfasting like a Nordic fisherman with a side order of fortified everything.
The UK Deficiency Problem
Low vitamin D is not some boutique complaint reserved for people who collect wellness gadgets and panic at the sight of a croissant. Dr Brewer points to Public Health England findings showing that low blood levels are not rare across adults and teenagers.
“Public Health England found that 23% of adults aged 19-64 years, 21% of adults aged 65-plus, and 22% of children aged 11-18 have low blood levels of vitamin D. They therefore advise everyone should consider taking a supplement supplying 10 micrograms of vitamin D per day during autumn and winter months.
For anyone wondering whether this is simply another winter nag from the health cupboard, the numbers give it ballast. The official baseline advice is modest: consider 10 micrograms a day during autumn and winter. It is not glamorous. It will not make your kitchen look like a Californian biohacking laboratory. But it is practical.
Is 10 Micrograms Enough?
Here is where the story becomes more interesting. The minimum advice is designed to help prevent deficiency. That is not necessarily the same as saying every person, at every age and stage, is operating at their best.
Dr Brewer argues that some people may need more, particularly as they get older.
“However, this is the minimum needed to prevent vitamin D deficiency conditions, such as muscle and bone aches and pains, osteomalacia or rickets. For optimum health, there is increasing evidence that higher doses of 25mcg to 50mcg vitamin D are needed, especially for older people as the ability to synthesise vitamin D declines in later life.
This is the sort of point that gets lost when health advice is reduced to a fridge magnet. Preventing deficiency is one thing. Supporting the body through winter, ageing and lower sunlight exposure may require a more thoughtful conversation.
Why Sunshine Alone May Not Save You
It is tempting to imagine that a bright day solves the matter. Roll up the sleeves, point yourself at the sky, job done. Sadly, biology is not quite so obliging. Sunscreen, clothing, ageing skin and long exposure all complicate the picture.
“Even when the sun is shining, many people fail to synthesise sufficient vitamin D, because they cover up, use high SPF sunscreens, or stay in the sun for more than 20 minutes which causes inflammation (sunburn) that breaks down the vitamin D they’ve already produced. Age also plays a role – we make four times less vitamin previtamin D3 in the skin over the age of 60 than in our 20s.
That last line should make anyone over 60 raise an eyebrow, preferably from beneath a sensible hat. The body’s ability to manufacture vitamin D changes with age, so advice that worked in your twenties may not be quite so persuasive later on.
The Biology Is Not As Simple As Sun Equals Success
The body does not simply collect sunlight and file it neatly under “sorted”. The vitamin D pathway involves conversion processes, and Dr Brewer notes that even high sunshine exposure does not guarantee ideal status.
“The synthesis of active vitamin D is quite complicated and the pre-vitamin D made in the skin must undergo two further conversions in the liver, then in the kidneys/other tissues, to become active. [Another study found] among 93 fit, healthy surfers in Hawaii, for example, more than half had low vitamin D status despite achieving 29 hours of sunshine exposure per week. This may partly be due to genetic inefficiencies of vitamin D3 metabolism, and partly because longer sun exposures cause the rapid breakdown of previtamin D3 in the skin.
That example is wonderfully inconvenient. If fit, healthy surfers in Hawaii can come up short despite living the sort of sun-drenched existence most Britons only encounter on screensavers, the rest of us should probably avoid looking smug after a ten-minute walk to the station.
Vitamin D3 Or D2?
For supplement shoppers, the label matters. Dr Brewer recommends looking specifically for vitamin D3, rather than assuming every form is equal.
“Take a supplement supplying at least 10mcg vitamin D3 (and preferably 25mcg) per day. Those aged over 50 may need 50mcg per day to offset lower production in the skin and reduced dietary absorption. The European Food Safety Authority has suggested a tolerable upper safe level for long-term use from supplements of 100mcg vitamin D3 per day. Select supplements providing vitamin D3, which is more effective than the plant form known as vitamin D2 for maintaining vitamin D status.”
That is a useful distinction. Vitamin D3 is the form Dr Brewer favours for maintaining vitamin D status, and her advice is especially pointed for older adults, whose skin production and dietary absorption may not be what they once were.
The Sensible Winter Takeaway
None of this requires melodrama. It requires paying attention. In the UK, autumn and winter are not merely colder; they are darker in a way that changes the body’s opportunity to make vitamin D naturally.
Food sources such as oily fish, liver products, eggs, butter and fortified foods may help, but Dr Brewer’s point is clear: many people will not get enough from diet alone during winter. Supplementation, particularly with vitamin D3, is the practical route she highlights.
The British winter is not known for generosity. It gives us drizzle, early darkness and a collective urge to stand near radiators. If vitamin D is one small way to help the body through the season, it seems rather sensible to treat it less like an afterthought and more like essential kit — somewhere between a decent waterproof and remembering where you left the car keys.
