Irish winters may not be sunny, but we still get vitamin D

New research shows enough UVB shines through during ‘vitamin D winter’

There’s enough sun in Ireland during winterto promote vitamin D, according to new research. Photograph: Eric Luke

There’s enough sun in Ireland during winterto promote vitamin D, according to new research. Photograph: Eric Luke


Irish winters may not be sunny, but we are still getting our vital supply of vitamin D.

A new study from Trinity College Dublin in collaboration with Ulster University has put paid to the myth that Irish sunshine is too weak to encourage any vitamin D production in the skin during the “vitamin D winter”, estimated to last from about October to April.

Using data from European Space Agency (ESA) satellites to measure Ultra Violet B (UVB) levels over Ireland, the researchers found that a strong relationship between sunshine and vitamin D persists in the Northern hemisphere, including Ireland.

The study found while UVB levels are much less in the colder part of the year, they are far from zero.

Researchers from Trinity’s School of Medicine used the ESA’s satellites to accurately account for sunshine levels over a period of time, in the area that each individual in the study lived.

This is the first time these satellites have been used in research on vitamin D and UVB exposure or personalised to this extent in a study.

UVB has also been largely ignored in previous research, due to the difficulty of measuring it accurately, particularly in large numbers of adults living across a geographical location.

All 5,138 participants in the study were older adults (aged 60 and over) as the ability to synthesise vitamin D in the skin is known to decrease with age.

Researchers were able to measure, based on where participants lived, the amount of exposure they got to sunshine over the previous five months, and analyse how important their exposure to sunshine was to vitamin D levels.

“These findings are especially important as the prevalence of vitamin D deficiency in Ireland is quite high, especially among the elderly, and although it might not seem like we get a lot of sunshine, in actual fact the sunshine we do get is still a very important source of vitamin D,” said researcher Fiona O’Sullivan.

Large differences in ambient UVB between the north and south of the country were also found.

There was a 19 per cent higher yearly UVB in Mizen Head than Malin Head, even though Ireland is a relatively small country.

The researchers found considerable differences between the east and west of the country, especially in the summer time, giving greater meaning to the phrase “The Sunny South East”.