Researchers from the Peninsula Medical School, the University of Cambridge and the University of Michigan, have for the first time identified a relationship between Vitamin D, the "sunshine vitamin", and cognitive impairment in a large-scale study of older people. The importance of these findings lies in the connection between cognitive function and dementia: people who have impaired cognitive function are more likely to develop dementia.

The study was based on data on almost 2000 adults aged 65 and over who participated in the Health Survey for England in 2000 and whose levels of cognitive function were assessed. The study found that as levels of Vitamin D went down, levels of cognitive impairment went up. Compared to those with optimum levels of Vitamin D, those with the lowest levels were more than twice as likely to be cognitively impaired.

Vitamin D is important in maintaining bone health, in the absorption of calcium and phosphorus, and in helping our immune system. In humans, Vitamin D comes from three main sources – exposure to sunlight, foods such as oily fish, and foods that are fortified with vitamin D (such as milk, cereals, and soya drinks). One problem faced by older people is that the capacity of the skin to absorb Vitamin D from sunlight decreases as the body ages, so they are more reliant on obtaining Vitamin D from other sources.

According to the Alzheimer's Society, dementia affects 700,000 people in the UK and it is predicted that this figure will rise to over 1 million by 2025. Two-thirds of sufferers are women, and 60,000 deaths a year are attributable to the condition. It is believed that the financial cost of dementia to the UK is over £17 billion a year.

Dr. Iain Lang from the Peninsula Medical School, who worked on the study, commented: "This is the first large-scale study to identify a relationship between Vitamin D and cognitive impairment in later life. Dementia is a growing problem for health services everywhere, and people who have cognitive impairment are at higher risk of going on to develop dementia. That means identifying ways in which we can reduce levels of dementia is a key challenge for health services." 

Dr Lang added: "For those of us who live in countries where there are dark winters without much sunlight, like the UK, getting enough Vitamin D can be a real problem – particularly for older people, who absorb less Vitamin D from sunlight. One way to address this might be to provide older adults with Vitamin D supplements. This has been proposed in the past as a way of improving bone health in older people, but our results suggest it might also have other benefits. We need to investigate whether vitamin D supplementation is a cost-effective and low-risk way of reducing older people's risks of developing cognitive impairment and dementia."

The paper will appear in a forthcoming issue of the Journal of Geriatric Psychology and Neurology.