Summer just feels like a healthier season – plenty of daylight after work to play soccer or picnic in the park, beach days, and a free boost of vitamin D from all that extra sunshine.
It’s like a reset button for body and mind.
But when it comes to replenishing your vitamin D, depleted by so much indoor time and skin-covering layers over the winter, that extra time outside might not be enough.
A new study from Newcastle University in the UK, published in the European Journal of Clinical Nutrition, found that even during the brightest months of the year, vitamin D insufficiency remained stubbornly common for the majority of people tested.
“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,” says nutrition researcher Bernard Corfe.
Between December 2024 and August 2025, Corfe and his colleagues tested 299 people for vitamin D levels using a simple finger-prick blood test. About half of them were over 65, and the other half were people over 18 who had darker skin.
Among adults aged 65 and older, almost 55 percent had vitamin D levels below the recommended threshold. The picture was even more striking for adults with darker skin, where more than 72 percent fell below that level.
Despite testing beginning in winter and moving into spring and summer, those numbers barely changed.
That’s a problem because vitamin D plays a key role in keeping bones healthy by helping the body absorb calcium, which is especially important for older adults. It’s also involved in muscle function and immune health, and it may even affect mental health.
A large meta-analysis published in 2022 in Critical Reviews in Food Science and Nutrition linked higher vitamin D to fewer depressive symptoms in those diagnosed with depression.
There’s plenty of disagreement about some of the health claims though, with some scientists calling studies linking vitamin D to lower cancer or diabetes risk overblown. Research is ongoing.
Unlike most vitamins, vitamin D is something we can both consume in our food and make ourselves.
frameborder=”0″ allow=”accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share” referrerpolicy=”strict-origin-when-cross-origin” allowfullscreen>Our skin manufactures vitamin D when it’s exposed to ultraviolet B (UVB) rays from sunlight.
That’s why deficiency is often thought of as a winter problem – shorter days and weaker sunshine leave our vitamin D factories running below capacity.
But the new study suggests that for some people, that summer boost simply doesn’t arrive.
Why? There are three key reasons. First, age: As we get older, our skin becomes less efficient at producing vitamin D from sunlight. Older adults may also spend less time outdoors.
Skin pigmentation matters too.
Melanin, which gives skin its color, acts like a natural sunscreen, blocking UV rays. While that can protect against skin damage, it also means people with darker skin generally need more sun exposure to produce the same amount of vitamin D as someone with lighter skin.
Geography also has a huge impact on how much sun you need to produce enough Vitamin D. Northern Britain, where this study was done, sits at a latitude where sunlight is relatively weak for much of the year, and even summer may not provide enough UVB exposure for everyone.
Even if you live at lower latitudes, it might not be safe to sunbathe for other reasons.
In sunny Valencia, Spain, researchers found you’d need to sit in the noon sun for 7 minutes in July – which sounds great until you realize it can be over 38 degrees Celsius (100 degrees Fahrenheit) in the sun in summertime Spain, which is both uncomfortable and potentially dangerous.
For comparison, it would take about 2 hours a day to get enough sunshine to meet vitamin D needs in the winter there.
The authors of the new study say their findings challenge the common assumption that summer sun is enough.
“For people living in places like the North of England, this shows that sunlight alone may not be enough, particularly for older adults and those from minoritized ethnic backgrounds,” says Bernard Corfe, a nutrition researcher at the University of Newcastle.
“The message is simple but important. If you are in a higher-risk group, you can’t assume that spending more time outdoors in summer will solve the problem.
They write plainly that year-round supplementation is “crucial.”
An important caveat of this study is that all 299 participants had low vitamin D levels to begin with, and those taking vitamin D supplements were excluded.
That means the results shouldn’t be taken as evidence that half of all older Britons or nearly three-quarters of all ethnic minority adults are vitamin D insufficient, since many people do take those supplements.
But if not, the findings reinforce what many public health experts have suspected: for some groups, relying on sunshine alone simply isn’t enough.
It’s important to note that the study was wholly funded by BetterYou Ltd, a UK-based health and wellness company that makes and sells nutritional supplements.
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Current UK guidance already recommends that everyone over the age of 4 consider taking a 400IU vitamin D supplement daily between October and March.
“We need to be thinking about more consistent, year-round ways to support healthy vitamin D levels,” says Corfe.
People at higher risk of deficiency – including many older adults and those with darker skin – may benefit from supplementation throughout the year.
In the US, the guidance is 600 IU of vitamin D for children and adults, and 800 IU for those aged 70 and over.
Unlike some vitamins, though, where excess just gets flushed through your body, you can take too much vitamin D.
High doses can be toxic, so be sure to consult with your doctor and follow the recommended doses.
This research was published in the European Journal of Clinical Nutrition.
This article was fact-checked by Clare Watson and edited by Rebecca Dyer. While we pride ourselves on our process, we are only human. If you spot a mistake, please let us know.
