Vitamin D deficiency is common among adults over the age of 50 in Ireland, new research has found.

According to the latest findings from The Irish Longitudinal Study on Ageing (TILDA), an ongoing study of people over 50 carried out by researchers at Trinity College Dublin (TCD), one in eight older adults is deficient in vitamin D and this increases to one in four during the winter months.

Vitamin D is essential for good bone health, and is also thought to have beneficial effects when it comes to muscle strength and non-skeletal health.

The main source of vitamin D is ultraviolet B (UVB) radiation from the sun, however this can be affected by factors such as sunscreen use, cloud cover and seasons.

The vitamin is also found in certain foods such as oily fish like mackerel and salmon, cheese, egg yolks and foods fortified with vitamin D, such as milk and cereals.

There have been calls for a wider range of foods to be fortified. However before this occurs, comprehensive information is needed on the prevalence and determinants of vitamin D deficiency, particularly in older adults who are most at risk.

The TILDA researchers set out to examine the prevalence of vitamin D deficiency and the reasons for this. They said that their results are not just relevant to Ireland , but all countries that experience seasonal variation in sunlight.

They found that one in eight older adults were deficient in vitamin D and even during the summer months, when the body normally produces vitamin D, 5% of adults were deficient.

Deficiency increased with age. For example, 22% of people aged 50-59 were vitamin D deficient in the winter months, but among people over the age of 80, this increased to 37%.

Deficiency was more common among smokers (23%), people who live on their own (21%) and those from a lower socio-economic background (17%).

People were also much more likely to be deficient if they were physically inactive or if they lived in the north or west of Ireland.

Meanwhile, very few people over the age of 50 took vitamin D supplements - just 8.5%.

"This is the largest representative study of the vitamin D status of older adults ever conducted in Ireland and is also one of largest in the world. There are striking differences in the prevalence of deficiency across different physical and lifestyle factors, such as obesity, smoking and physical inactivity, all of which are modifiable risk factors," commented the study's lead author and research fellow at TILDA, Dr Eamon Laird.

He said that he hoped the findings would provide useful data to help inform public health policy, particularly in relation to the issues of fortification and supplementation.

"To place this in context, in a country such as Finland, which gets less sunlight than Ireland and is at a more northern latitude, it actually has less prevalence of vitamin D deficiency than Ireland due to a comprehensive public health policy of supplementation and fortification," Dr Laird explained.

Also speaking about the findings, Prof Rose Anne Kenny, principal investigator of TILDA, emphasised that vitamin D is needed for normal bone health and for the prevention of serious chronic conditions, such as osteoporosis.

"Furthermore, new research has shown that vitamin D deficiency may also be associated with heart disease, kidney disease, brain health and diabetes. If these associations are confirmed in other large studies, then the high rates of deficiency seen in the older adult population are of concern and, given that vitamin D can be treated easily with supplementation, this has significant policy and practice implications for Government and health services," she insisted.

Details of these findings are published in the Journal of Gerontology: Medical Sciences.