More than half of older patients and nearly three-quarters of ethnic patients screened for a vitamin D supplementation trial in northern Britain had vitamin D insufficiency or deficiency, suggesting that clinicians should not assume vitamin D status improves during summer in these higher-risk groups.
In a study published in the European Journal of Clinical Nutrition, researchers reported that 55% of older patients and 72% of ethnic patients had serum 25-hydroxyvitamin D levels below 50 nmol/L, the threshold used to define vitamin D insufficiency or deficiency. The prevalence of low vitamin D status showed little evidence of declining during summer months.
The findings came from screening data collected between December 2024 and August 2025 for an ongoing clinical trial investigating vitamin D supplementation in older adults and ethnic adults with darker skin pigmentation. Researchers screened 299 patients living in Britain, including 168 patients aged 65 years and older and 147 ethnic patients aged 18 years and older with Fitzpatrick skin types IV to VI. Vitamin D status was assessed using dried blood spot samples analyzed by liquid chromatography–tandem mass spectrometry.
Mean serum 25-hydroxyvitamin D levels were approximately 50 nmol/L among older patients and 40 nmol/L among ethnic patients. Vitamin D insufficiency or deficiency remained common across the recruitment period, with monthly analyses showing little seasonal variation. Among older patients, prevalence did not fall substantially during summer recruitment months, while ethnic patients maintained consistently high rates of insufficiency throughout winter, spring, and summer.
Among older patients, the prevalence of vitamin D insufficiency or deficiency during June through August was 56%, exceeding estimates previously observed in the general UK population. Ethnic patients also had consistently higher rates of insufficiency than older patients throughout the study period.
The study was not designed to determine why vitamin D insufficiency remained common in these groups. Researchers suggested that diet, skin pigmentation, and cultural practices may contribute to vitamin D status among ethnic patients, although these factors were not directly evaluated. Exploratory analyses did not identify an association between body mass index and vitamin D status.
Several limitations may affect interpretation of the findings. The analysis was based on patients screened for a clinical trial rather than a population-based sample, which may limit generalizability. Researchers also did not collect data on liver function or polypharmacy, factors that could influence vitamin D status. In addition, all older patients were free-living and did not reside in care homes or sheltered accommodation.
In their conclusion, lead study author Alice Goddard, of Newcastle University, and colleagues wrote that the findings "highlight persistently high rates of vitamin D insufficiency across high-risk groups in northern Britain and underscore the inadequacy of sunlight exposure as a corrective measure."
Disclosures: BetterYou Ltd funded the study. Researchers reported that the sponsor was not involved in the study design, delivery, or interpretation of the data. The investigators declared no conflicts of interest.