Nearlyone in every eight people in Ireland is deficient in vitamin D - which is necessary for healthy bones in adults and children.
shortage of this important vitamin leads to rickets among children - a bone disease which had been largely eradicated but has now begun to re-emerge among babies here.
The vitamin deficiency can also cause bone disease and pain in adults.
Most vitamin D is created in the skin when it is exposed to sunlight. However, the lack of strong sunshine in Ireland means that levels must be topped up by supplements or a dietary source.
Oily fish such as salmon, sardines and mackerel are all good food sources of vitamin D.
It can also be found in eggs, fortified fat spreads, breakfast cereals and some powdered milks.
The lack of the vitamin here is found across the population, according to a team of researchers from University College Cork (UCC).
However, darker-skinned people living in Ireland are particularly at risk as they can require up to 50 times more sunlight to produce the same amount of vitamin D as fair skinned people.
Professor Kevin Cashman and Professor Mairead Kiely of UCC's Cork Centre for Vitamin D and Nutrition Research found that around 12pc of the population is deficient in vitamin D here.
The rate is as high as 20pc in the UK.
Prof Cashman said: "While sunlight is a key provider, it is not strong enough during winter months to allow the skin to make vitamin D.
"In addition, even in summer, public health advice suggests limiting unprotected sun exposure due to important concerns about skin damage and cancer."
He said the alternative source of vitamin D was food. However, the amount in the diet of many Europeans has been shown to be low.
The findings emerged in a European Commission-funded analysis of vitamin D status in 18 nationally or regionally representative studies of European children, teenagers, adults and the elderly.
The data involved 55,844 individuals stretching from Crete to Troms, in Norway, for the study in 'American Journal of Clinical Nutrition'.
The UK's health watchdog has advised that people can expose their arms and legs to the sun for short periods to help build up vitamin D.
A short period of time in the sun would involve just 10-15 minutes for typical Irish skin.
Longer than this could expose the skin to a risk of sunburn and damage.
Some groups, such as babies, young children from six months to five, as well as the over-65s and pregnant women, should be given a vitamin D-only supplement to top up levels in the body.
Anyone who is in any way unsure about whether they need a supplement should discuss the matter with their public health nurse or GP.