Vitamin D is found in some foods including oily fish and eggs and is also produced when skin is exposed to sunlight. However, ageing diminishes the skin’s ability produce vitamin D.

The research team studied 850 older people (65+) living in Italy, with participants’ cognitive function assessed across a variety of common tests.

Compared to participants with healthy levels of vitamin D, those who were severely deficient in the vitamin were 60 per cent more likely to experience substantial general cognitive decline, and 31 per cent more likely to experience new problems with mental flexibility. The researchers describe the results as “the first...to identify a clear link between low vitamin D levels and cognitive decline.”

The study leader, Dr. David J. Llewellyn, went on to say of the findings:
“Cognitive decline and dementia are very common in older adults, though the underlying causes are still largely unknown and current options for prevention and treatment are limited. Vitamin D deficiency is therefore a highly promising therapeutic target for the prevention of dementia.”

Dr Simon Ridley, Head of Research for the Alzheimer’s Research Trust, said:
“This study has identified a promising association between vitamin D levels and cognitive function. To be certain of whether vitamin D has a protective effect, we need to see comprehensive clinical trials.

“Research is the only answer to dementia. We must invest in research urgently to deliver the treatments needed tackle the UK’s dementia crisis.”