A winter sun escape feels like the obvious fix when the UK clocks go back on 25 October and daylight shrinks until March. But according to Dr Sohère Roked, a GP and functional medicine specialist, a week in the sun is only a temporary top-up — levels typically dip again within a few weeks of returning to grey British skies. Worth doing, then, but not a substitute for a daily supplement.
The numbers back up the concern. The government's National Diet and Nutrition Survey found 18% of adults aged 19 to 64 have low vitamin D, climbing to 31% between January and March. Since sunlight is our main source — UVB rays trigger production in the skin — the UK's winter sun angle is simply too weak to help, no matter how long you stay outdoors. Food sources like oily fish and eggs contribute, but rarely enough. Low mood, frequent colds, aches and general sluggishness can all point to deficiency, and a blood test is the only reliable way to confirm it.
There's a travel angle beyond the beach, though. Destination choice genuinely affects your dose. Snow reflects up to 80% of UV rays, so ski trips are surprisingly effective for vitamin D — altitude strengthens UV further — which is also why slope-side sun protection matters. Sand reflects around 15%, giving beach holidays a smaller but real boost. On the flip side, if you're heading north for a Northern Lights trip, or somewhere cloudy or heavily polluted, pack your supplements, since cloud, smog and high latitude all cut UVB.
Two myths worth busting. First, skip the sunscreen and you'll soak up more vitamin D? No — most people don't apply or reapply SPF thoroughly enough to block production anyway, so keep it on. Second, you can't top up through glass: UVB is blocked almost entirely by windows, whether on a plane, in a car or behind a balcony door, even though UVA gets through.
On the supplement side, the NHS advises everyone to consider 10 micrograms (400 IU) daily through autumn and winter, with people with darker skin tones advised to consider a year-round round, as higher melanin reduces skin's production ability. Older travellers, those with higher body fat, people who cover up or stay indoors, and those on certain medications including steroids and anticonvulsants may also need more. Dr Roked suggests 1,000-2,000 IU daily as a sensible baseline for most adults, ideally vitamin D3 (more effective than D2 — vegans should look for lichen-derived versions), taken with a fatty meal for absorption. Watch for accidental double-dosing from protein shakes and multivitamins, too, since toxicity comes from over-supplementation rather than sunshine. And if you see D3 paired with K2, that's deliberate: K2 helps direct calcium into bones.
The takeaway for holiday planners: book the winter sun trip for your mood as much as your health, but treat it as a bonus. Consistency — a daily supplement taken year-round — matters more than any single getaway.
