Study finds summer sunlight often fails to restore vitamin D levels

Newcastle University said a study published June 4 found that summer sunlight did not reliably restore vitamin D levels in nearly 300 people across northern Britain. The pattern held in two groups already known to face higher risk: adults aged 65 and older, and people from minoritized ethnic backgrounds of all ages.

The findings matter because vitamin D supports healthy bones and overall wellbeing, and low levels have been linked to osteoporosis, rickets and weakened immune function. In the study, more than half of the older adults had insufficient vitamin D, and the share was even higher among participants from minoritized ethnic backgrounds. Levels did not meaningfully improve during the summer months, undercutting the common assumption that a few brighter weeks are enough to fix the problem.

The work was led by Newcastle University’s Human Nutrition and Exercise Research Centre and published in the European Journal of Clinical Nutrition under the title, Circannual prevalence of vitamin D insufficiency in older and minoritized ethnic adults in Northern Britain: screening outcomes from a clinical trial (ISRCTN13778806). Participants were recruited locally through community and online approaches, completed finger-prick blood tests, and had samples analyzed by a specialist laboratory. The study was funded by Better You Ltd, a UK supplement company.

Bernard Corfe, professor of human nutrition and health at Newcastle University and a co-leader of the study, said sunlight alone may not be enough for higher-risk groups, especially in the North of England. That warning is especially relevant in higher-latitude places where skin pigmentation, age, diet and lifestyle can all affect how much vitamin D the body makes, even when people spend time outside.

Newcastle University said the results point toward more targeted public health action, including clearer messaging, brief checks during GP appointments and supplementation where appropriate. For clinicians and families, the study is a reminder that vitamin D strategy cannot be one-size-fits-all, particularly for older adults and minoritized ethnic communities whose levels may stay low across the year.