Vitamin D deficiency is widespread throughout Dublin and surrounding areas, a major new study has found.

According to the findings, one in six people in Dublin is deficient in this key vitamin all year round, while this rises to one in four during the winter months.

Vitamin D is important for bone and muscle health and it also helps support a healthy immune system. It is known as the sunshine vitamin because it is produced in the skin by exposing the body to just 10-15 minutes per day of sunshine. In Ireland, vitamin D can only be produced in the skin between late March and late September. It cannot be produced in winter.

The alternative to sunshine is consuming vitamin-D rich foods or taking a vitamin D supplement.

However, this new study, which was one of the largest of its type ever carried out in Europe, has found that despite these different methods of obtaining vitamin D, deficiency is common in Dublin.

Researchers from the Mercer's Institute for Successful Ageing (MISA) and Trinity College Dublin (TCD) looked at over 36,000 people over the five-year period 2014-2018.

Using a tool known as geo-mapping, they were able to create a visual map of vitamin D levels across Dublin and east Leinster.

They identified large variations in vitamin D status between adults of different ages and locations. Those most likely to be deficient were people over the age of 80, and surprisingly, young adults in the 18-39 age group.

Overall, men were found to have much lower levels than women.

When it came to specific areas, vitamin D deficiency levels were lower in south Dublin and north Kildare compared to north Dublin and west Dublin.

While vitamin D levels were lowest in the winter, those living in inner city Dublin and west Dublin had the highest rates of deficiency all year round.

According to MISA research fellow and the study's first author, Helena Scully, this study found lower levels of vitamin D in Irish adults than in a previous population-based study, which suggests that deficiency "is more of an issue than once thought".

"It's important that the public is aware of the need to also get vitamin D through the diet and/or supplements, especially in the winter. Ensuring adequate levels of vitamin D in your diet can support bone health and normal function of your immune system.

"It's also important in young adults where peak bone density isn't reached until about the mid-20's. Eating a balanced diet and including dietary sources of vitamin D, such as oily fish, like salmon and mackerel, and also fortified foods, such as cereals and fortified milk, is important," she explained.

Meanwhile, according to senior research fellow at the TCD's School of Medicine, Dr Eamon Laird, these findings show that vitamin D deficiency "is not just an 'older adult' problem".

"Yet again we see more widespread vitamin D deficiency in our population with men, younger adults and the less affluent areas worst affected. Rates of deficiency have not improved therefore education to our identified at-risk groups, who are often forgotten, around the importance of vitamin D in the diet is crucial," he said.

Dr Kevin McCarroll, a consultant physician at St James's Hospital in Dublin and co-author of the study, said that the 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.

"The study highlights how vitamin D deficiency is relatively common and affects all age groups. Increasing vitamin D intake in the winter when deficiency is prevalent is a good idea for many people," he added.

This study was partially funded by Avonmore and details of these findings are published in the journal, Nutrients.