For decades the British public-health line on vitamin D ran roughly like this: get outside in the summer, top up your stores, and you’ll coast through the dark months on what you banked in July. Tidy advice. Free. The kind of guidance that costs the National Health Service nothing and asks nothing of anyone. A team at Newcastle University went and measured whether it was actually true, and the answer they got back was no.

Across nearly 300 people in northern Britain, screened between December 2024 and August 2025, the researchers found vitamin D insufficiency that didn’t budge for the season. More than half of the older adults they tested, 54.8 percent, sat below the 50 nmol/L threshold that marks insufficiency or outright deficiency. Among adults from minoritized ethnic backgrounds, with darker skin that synthesizes less vitamin D from the same dose of sun, the figure was 72.1 percent. Roughly seven in ten.

What should give the NHS messaging team pause is what happened in summer, which was nothing. The older adults screened in June, July and August came in at 55.6 percent insufficient, a hair worse than the annual figure rather than better. The seasonal rebound that the whole “soak up the sun” model leans on simply did not show up in the people most likely to need it.

“What’s striking about these findings is that vitamin D levels didn’t improve, even in the summer months when we would usually expect them to recover,” said Bernard Corfe, the Newcastle professor of human nutrition who led the work. “If you are in a higher-risk group, you can’t assume that spending more time outdoors in summer will solve the problem.”

He’s right, and it matters, because the advice has quietly failed the exact people least equipped to absorb the failure. The elderly make less vitamin D in the skin and spend less time in direct sun. Dark-skinned residents synthesize less of it in a country that sits at the latitude of Labrador, where for most of the year the sun over Newcastle never climbs high enough to drive meaningful synthesis at all. Telling a 78-year-old in Sunderland or a British-Pakistani family in Bradford to get more summer sun is, on this evidence, advice aimed at people it cannot reach. The mainstream “go outside” reflex earned this correction.

Now for the detail the press release mentions in passing and most of the coverage skipped.

The study was funded by BetterYou Ltd, a UK company whose business is selling vitamin D, specifically oral sprays. The funding statement does the customary thing and assures readers the company had no role in the design, conduct, or interpretation, and nothing in the prevalence data gives you reason to doubt it. The numbers are believable and line up with a decade of literature on vitamin D status at northern latitudes. Deficiency in these groups is not a manufactured crisis; it is a well-documented one.

But look at the conclusion that landed in every headline: summer sun isn’t enough, and people need “more consistent, year-round ways to support healthy vitamin D levels.” Which is to say, supplements. The product the funder sells. And the scientist delivering that line is the same Bernard Corfe who led a BetterYou-funded absorption trial concluding the company’s oral spray raised vitamin D levels just as well as a capsule, the kind of result BetterYou cites to sell the spray, and who has held BetterYou research grants before this. None of it is hidden. All of it sits in the small print, disclosed exactly as the rules require. The disclosure is as much the story as the data.

Here the reflex is to pick a side, and you don’t have to. The deficiency is widespread whether or not a spray company paid to measure it; the summer-sun advice fails these groups whether or not the fix comes in a branded bottle. A finding can be true and convenient at once, and the convenience doesn’t make it false. What the convenience tells you is who was always going to fund this particular question, and which answer they were hoping to print.

What changes on the ground is modest but worth naming. The screening came out of a larger supplementation trial testing “personalized and culturally appropriate” ways to raise vitamin D, and the researchers’ own recommendations are cheap and defensible: fold a brief vitamin D check into an existing GP visit for people in the high-risk groups, and stop pretending the reassuring summer line holds for the older and minoritized adults this study actually measured, because for them it plainly didn’t. The UK already advises a winter supplement for the general population. This nudges that toward year-round for the people the sun was never reaching.

What doesn’t change is the oldest rule in reading a trial: look at who paid before you decide what the result proves. Here the data say deficiency is widespread and stubborn, and that is almost certainly true. The recommendation says reach for the supplement, and that may well be sensible. It’s just that the company most enriched by your believing it is the one that signed the check, and a careful reader keeps both facts in view at once.

Sources

  1. European Journal of Clinical Nutrition – Goddard et al., “Circannual prevalence of vitamin D insufficiency in older and minoritized ethnic adults in Northern Britain” (2026)
  2. medRxiv preprint – full screening-outcomes paper with seasonal prevalence figures (ISRCTN13778806)
  3. EurekAlert – Newcastle University release with Bernard Corfe quotes
  4. ScienceDaily – “Study challenges a common belief about vitamin D and sunlight”
  5. ScienceDaily (2019) – Corfe-led University of Sheffield/BetterYou trial finding the oral spray as effective as a capsule
  6. BetterYou – company statement on funding university vitamin D research