Researchers Discover a Hidden Vitamin D Problem That Persists Year-Round

A new study suggests that some groups may not experience the expected seasonal boost in vitamin D levels, even during the sunniest months of the year.

Many people assume that spending more time outdoors during summer naturally restores vitamin D levels after the darker winter months. But new research suggests that for some groups, that seasonal boost may never arrive.

Researchers at Newcastle University found that vitamin D levels remained consistently low throughout the year among older adults and people from minoritized ethnic backgrounds in northern Britain. The findings suggest that vitamin D insufficiency may be a persistent, largely unnoticed health issue for many individuals, even during periods of increased sunlight exposure.

Published in the European Journal of Clinical Nutrition, the study analyzed vitamin D levels in nearly 300 participants. More than half of the adults aged 65 and older had insufficient vitamin D levels, while rates were even higher among participants from minoritized ethnic groups.

A Deficiency That Doesn’t Disappear With the Seasons

What surprised researchers most was that vitamin D levels showed little improvement during summer. This challenges the long-held belief that a few months of sunnier weather are enough to replenish the body’s vitamin D reserves.

That assumption may be especially problematic in northern regions, where sunlight is weaker for much of the year. Vitamin D is produced when ultraviolet B (UVB) rays from the sun reach the skin, but factors such as age, skin pigmentation, clothing, sunscreen use, and geographic location can all reduce the body’s ability to make it. Older adults also produce vitamin D less efficiently than younger people.

Vitamin D plays a critical role in helping the body absorb calcium and maintain healthy bones. Low levels have been linked to osteoporosis, rickets, muscle weakness, and impaired immune function. Growing research has also explored potential connections between vitamin D status and a range of chronic health conditions, although many of those relationships remain under investigation.

Researchers Call for a Different Approach

Bernard Corfe, Professor of Human Nutrition and Health at Newcastle University and co-leader of the study, said: “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.

“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.

“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.

“We need to be thinking about more consistent, year-round ways to support healthy vitamin D levels.”

A Potential Public Health Blind Spot

To conduct the study, researchers recruited participants through community outreach and online channels. Each volunteer completed a simple finger prick blood test, with samples analyzed by a specialist laboratory.

The results point toward a need for more targeted public health strategies. Researchers suggest that clearer guidance about vitamin D, routine discussions during primary care visits, and appropriate supplementation could help reduce the risk of long-term deficiency.

The study also helps fill a gap in understanding how vitamin D levels change throughout the year in groups known to face a higher risk of deficiency. The next phase of the research will explore personalized and culturally appropriate ways to improve vitamin D status, including tailored dietary guidance and healthcare approaches designed to better meet the needs of diverse communities.

Reference: “Circannual prevalence of vitamin D insufficiency in older and minoritized ethnic adults in Northern Britain: screening outcomes from a clinical trial (ISRCTN13778806)” by Alice Goddard, Anthony Watson, Rowena Tilbury, Bernard M. Corfe and Andrea Fairley, 19 May 2026, European Journal of Clinical Nutrition.
DOI: 10.1038/s41430-026-01760-z

The research was funded by Better You Ltd, a UK-based health and wellness company that makes and sells nutritional supplements. The research funder was not involved in the study design, delivery, or interpretation of the data, which was carried out entirely by Newcastle University.