Most of us know sunlight plays a key role in vitamin D production — but where you live dramatically shapes how much your body can actually make. Vitamin D insufficiency is increasingly recognised as a year‑round issue in northern latitudes, and new research from Newcastle University suggests the problem may be far more widespread than previously assumed.

At the heart of this is geography. The 37th latitude is often cited in scientific literature as the point at which the angle of the sun becomes too low for reliable UVB exposure. Above 37° North or South — including the whole of the UK, which sits between roughly 50°N and 59°N — the sun’s UVB rays simply don’t reach the earth at the right angle for much of the year. Between October and February, the atmosphere filters out the UVB needed to convert pre‑vitamin D3 in the skin. In other words: even if you’re outdoors, your body can’t make vitamin D.

But here’s the part that’s raising eyebrows. A new study published in the European Journal of Clinical Nutrition shows that vitamin D insufficiency persists all year round for many people in England — including during the summer months when we assume sunlight will “top us up”.

Vitamin D insufficiency studies

Researchers followed nearly 300 adults across northern Britain, focusing on two groups known to be at higher risk: adults aged 65+ and people from minoritised ethnic backgrounds. The findings were striking:

• Over half of older adults had insufficient vitamin D, even in summer.
• Rates were even higher among minoritised ethnic groups.
• For some individuals, summer sunlight didn’t raise levels at all, challenging the long‑held belief that sunshine alone is enough.
• The pattern was consistent enough that researchers emphasised the need for year‑round strategies, even for those living in southern England.
• Future research will explore personalised, culturally‑sensitive approaches to improving vitamin D status.

As the authors note, “Many people could be living with low vitamin D all year round without realising it. This has implications for bone health, general well-being and longer-term health risks.”

For practitioners, this reinforces what many already see in clinic: relying on seasonal sunlight is not enough for everyone, especially in northern climates. For individuals, it highlights the importance of moving from assumption to evidence.

The takeaway — even in southern Britain: test, don’t guess

If you’re unsure about your vitamin D status, a simple blood test can provide clarity. NHS teams and local pharmacies may offer guidance on testing options. Private GP‑led laboratories such as Medichecks (no affiliation) also provide accessible vitamin D testing. For a more comprehensive nutrient assessment, you can speak with a registered Nutritional Therapy Practitioner who can arrange advanced laboratory testing.

Understanding your vitamin D status isn’t about chasing perfection — it’s about supporting long-term health with informed, personalised choices. And for those of us living well above the 37th latitude, it’s a reminder that geography shapes biology more than we often realise.

Reference: Goddard et al. Circannual prevalence of vitamin D insufficiency in older and minoritised ethnic adults in Northern Britain. Eur J Clin Nutr (2026).