More than half of adults over the age of 50 have inadequate vitamin D levels, while one-quarter are considered deficient in the vitamin, new Irish research has revealed.

Vitamin D is known to have a key role in bone health, however there is growing evidence to suggest it is also important for muscle strength and other non-bone-related outcomes.

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.

Researchers at Trinity College Dublin (TCD) looked at over 6,000 middle-aged and older adults living in England, in order to identify those most at risk of deficiency.

According to the findings, 57% of people aged 50 and older have inadequate vitamin D levels, while 26% are deficient. This suggests that vitamin D deficiency is prevalent in older people living at northern latitudes.

The researchers found that those most at risk included women, people aged 80 or older, smokers, those with a non-white ethnicity, obese people and those in poor health.

Potentially protective factors against deficiency included maintaining a healthy weight, being retired, being engaged in regular vigorous physical activity, using a vitamin D supplement, sun travel in the last year and the summer season.

"Our study identified factors associated with vitamin D deficiency, including being aged 80+ years, obesity and sedentary lifestyles; all of which are increasing traits in western populations.

"Furthermore, this is one of the few studies to highlight the importance of non-white ethnicity in vitamin D deficiency in a large study of ageing. The findings are valuable in developing targeted strategies to eliminate vitamin D deficiency in older populations," commented associate professor in nutrition at TCD, Dr Maria O'Sullivan.

Meanwhile, according to the study's first author, Dr Niamh Aspell, while those who used a vitamin D supplement were, as expected, less likely to be deficient, supplement use was low (4%), ‘therefore food fortification and other strategies need to be considered at policy level for older populations'.

The study's co-author, Dr Eamon Laird, said that the high rates of deficiency seen in the study group are similar to rates seen in other high latitude countries such as Ireland.

"However, other more northern countries, such as Finland, have implemented a successful vitamin D fortification policy, which has all but eliminated deficiency in the population. Such a policy could easily be implemented in the UK and Ireland," he insisted.

Details of these findings have been published in the journal Nutrients.