Just get outside and get some sun is one of the most repeated pieces of vitamin D advice out there, and for a lot of people it holds up reasonably well once summer arrives. A new study out of Newcastle University found it does not hold up for everyone equally, and I wanted to look closely at who it leaves behind before repeating the advice myself.
Researchers screened nearly 300 adults in Northern Britain as part of a larger clinical trial, focusing on two groups, adults 65 and older, and adults from minoritized ethnic backgrounds. They found vitamin D insufficiency or deficiency in 54.8% of the older adults and 72.1% of the minoritized ethnicity adults. The part that broke from the usual pattern is that these rates barely moved across the seasons. For most people, vitamin D levels rise in summer and fall in winter. For these two groups specifically, they stayed roughly flat all year.
Two things are likely working against these groups at once. Skin becomes less efficient at producing vitamin D from sunlight as it ages, and higher melanin content also reduces how much vitamin D the skin can synthesize from a given amount of sun exposure. Put those together and summer sun simply does not deliver the same boost it gives everyone else.
This is one study, screening data from about 300 people in one region of Northern Britain, which sits at a much higher latitude than most of the United States. The exact percentages should not be assumed to apply directly to an American audience, and this is observational screening data from a clinical trial rather than a randomized supplementation trial, so it shows a pattern rather than testing a fix. No contradicting research turned up in my search, and the finding lines up with well established biology around aging skin and melanin, but it has not yet been independently repeated in a second study.
If you are over 65 or have more melanin in your skin, this is a real reason to treat vitamin D as a year round habit rather than something you only think about in winter. Getting your levels checked and talking to a doctor about supplementation, regardless of season, is a reasonable and low risk step worth considering for these two groups specifically.
Not for everyone. This study found older adults and adults from minoritized ethnic backgrounds stayed insufficient across seasons, unlike the general population pattern.
Aging skin and higher melanin content both reduce how efficiently skin produces vitamin D from sunlight, which likely explains why the usual seasonal boost does not show up.
Not exactly. This study was done in Northern Britain, a higher latitude than most of the US, so the specific percentages should be treated as specific to that population rather than a national number.
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