Around 13% of over-50’s were found to have vitamin D levels below the 30 nanomoles/ litre (nmol/l) deficiency threshold. Prevalence of deficiency increased during the winter period to around one in four adults. Even in summer, around 5% of elderly adults in Ireland were deficient, found the researchers from Trinity College, Dublin.
The frequency of vitamin D deficiency increased with age, with 37% of over-80s classified in this category. Smokers were also more likely to be deficient (23%), as were people living alone (21%) and those from a lower socio-economic status (17%). Physically inactive subjects, obese individuals and those living in the North and West of Ireland (less sunny than the South) were also more likely to be deficient.
In the combined winter/ spring period, 52% of men and 61% of women were classed as ‘insufficient’ according to the < 50 nmol/l blood concentration threshold. However, if the Endocrine Society Practice Guideline of 75 nmol/l adequacy threshold were applied, 81% of older Irish adults would be deemed as having vitamin D insufficiency.
The findings have implications for not just Ireland itself, but all other countries where sunlight is limited during periods of the year.
"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," said lead author and Research Fellow at TILDA, Dr Eamon Laird.
"We hope our findings will provide useful data to help inform public health policy -- in particular with regards to vitamin D food fortification and the targeting of vitamin D supplements -- aimed at reducing endemic vitamin D deficiency and identifying the population groups and location areas most at risk,”he added.
Serum Vitamin D levels were measured in 5,350 community dwelling Irish adults aged between 50 and 98 years from The Irish LongituDinal Study on Ageing (TILDA) cohort. Demographic, geographic, lifestyle and socio-economic variables were assessed by questionnaire. Deficiency prevalence was calculated for each season.
Public health implications
The study found very little use of vitamin D supplements - only 8.5% of the over-50’s population. Women (13%) were more likely to use them than men (4%), while 10% of non-obese subjects consumed them compared with 6% of obese individuals.
Laird contrasted the lack of supplementation (and food fortification) in the TILDA cohort with Finland, which has significantly longer seasonal periods of low sunlight than Ireland.
“To place this in context, in a country such as Finland, which gets less sunlight than Ireland and is at a more northern latitude, actually has less prevalence of vitamin D deficiency than Ireland (<1% vs 13%) due to a comprehensive public health policy of supplementation and fortification."
Professor Rose Anne Kenny, Principal Investigator of TILDA, further highlighted public health policy implications of the study findings.
"Sufficient vitamin D status is needed for normal bone health and for the prevention of debilitating 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 concluded.
Source: The Journals of Gerontology Series A
Published online, doi: 10.1093/gerona/glx168
“The prevalence of vitamin D deficiency and the determinants of 25(OH)D concentration in older Irish adults: Data from The Irish Longitudinal Study on Ageing (TILDA)”
Authors: Eamon Laird, Rose Anne Kenny, et al