One in four Irish over 50s are deficient in vitamin D during the winter, a new study has found.
The research also noted wide variations in vitamin D deficiency across Ireland, with the north and west having the highest rates.
Overall, one in eight people aged over 50 suffers from low levels of the vitamin, rising to one in four in the winter, the research from The Irish Longitudinal Study on Ageing (Tilda) at Trinity College Dublin shows.
Even during summer, when the body normally produces vitamin D, 5 per cent of adults were deficient.
Vitamin D deficiency rises with age, and is also higher among smokers, those living alone and people from lower socio-economic backgrounds, according to the study published in the Journal of Gerontology.
Vitamin D is essential for bone metabolism and is thought to have beneficial health effects for muscle strength and non-skeletal health. Voluntary fortification of only some food products currently occurs in Ireland, and there have been calls for a wider range of foods to be fortified with the vitamin.
Only 8.5 per cent of those surveyed were found to be supplementing their diet with vitamin D.
Principal investigator professor Rose Anne Kenny said the high rates of deficiency seen in the older adult population was of concern. "Given that vitamin D can be treated easily with supplementation, this has significant policy and practice implications for Government and health services."
Severe vitamin D deficiency causes rickets in children and osteomalacia, or softening of the bones, in adults. It may also increase the risk of many other chronic non-bone related diseases.
While sunshine helps the body produce vitamin D, this is not the only explanation for high levels of deficiency in Ireland. Finland, for example, which gets less sunlight and is more northerly, has a lower prevalence of vitamin D deficiency - less than 1 per cent against 13 per cent, due to a comprehensive public health policy of supplementation and fortification.
