The level of vitamin D Dubliners have in their system varies largely depending on which part of the city they live in, research has found.
A study, published in the journal Nutrients, using a tool known as geo-mapping, allowed researchers to create a map of vitamin D levels across Dublin and east Leinster.
It found large variations in vitamin D status between adults of different ages and locations.
Levels of the sunshine vitamin were lowest in winter, with those living in inner city Dublin and west Dublin having the highest rates of deficiency year round.
One in six adults living in Dublin and surrounds was vitamin D deficient, rising to one in four in winter.
The research was carried out by Mercer's Institute for Successful Ageing (MISA) and Trinity College Dublin.
Researchers noted that socioeconomic status is a factor, with those in typically disadvantaged areas having an increased risk of deficiency.
This may be due to factors linked to lower socioeconomic status including reduced dietary vitamin D intake, fewer sun holidays and possibly higher rates of obesity and smoking.
However, the study showed vitamin D deficiency is a problem for everyone.
Surprisingly the youngest participants in the study, those aged 18 to 39, had the lowest vitamin D levels.
One reason why younger adults may be deficient is that they may spend more time indoors, such as in their working environment.
Some areas such as south Dublin and north Kildare showed lower levels of vitamin D deficiency compared to north Dublin and west Dublin.
There were also big differences between postcodes of close proximity.
The prevalence of deficiency was high in participants located in some counties within and outside Leinster.
Vitamin D is important as it contributes to the maintenance of bone and muscle health and helps support a healthy immune system.
Dr Kevin McCarroll, study co-author and clinical senior lecturer and consultant physician at St James's Hospital, said the study highlighted how vitamin D deficiency is relatively common and affects all age groups.
"The striking differences in the prevalence of deficiency within Dublin and other areas is likely due to factors such as dietary vitamin D intake, supplement use, sun exposure and also ethnicity affecting the skin's capacity to make vitamin D from sunshine.
"Increasing vitamin D intake in the winter when deficiency is prevalent is a good idea for many people," he said.
The study was part funded by dairy company Avonmore.